Soaking Up the Heat

English
 
Prof. Avigdor Scherz and his team. Hot times
 
 
Humans are happiest in middling temperatures: When things get too cold, we turn to fires, radiators and overcoats; if too hot, to fans and air conditioners, to stay comfortable. Microorganisms do not have this luxury, yet without physical mechanisms to regulate internal body temperature or technology to alter their surroundings, they can be found happily thriving both in frozen Antarctica and in boiling hot springs.   
 
How do these bacteria and algae manage to get by in such extreme environments? If we could learn their secret, we might be able to use it to engineer crops that could grow in different climates or develop enzymes for industry that could work efficiently at different temperatures. Prof. Avigdor Scherz of the Plant Sciences Department and a team that included research students Oksana Shlyk-Kerner, Ilan Samish and Hadar Kless, and postdoctoral fellows Drs. David Kaftan, Neta Holland and P. S. Maruthi Sai, set out to find the mechanism used by organisms that flourish in extreme temperatures. 
 
In their experiment, the scientists worked with two different kinds of bacteria, both of them photosynthetic (that is, using the sun’s energy to create sugars for food). Employing a multidisciplinary approach, the research team focused on one of the key stages of photosynthesis, a reaction that takes place in enzymes in the “reaction center” of the bacterial cell. As they gradually raised the surrounding temperature, they timed the reaction to see how turning up the heat affected the reaction rate. 
 
They expected the change in rate to follow a general rule: As the temperature rises, the reaction should become faster and faster. To their surprise, neither bacterial enzyme obeyed the rule: Instead, they each peaked at a different temperature, after which the rate held steady, even as the temperature continued to rise. The peak for each microorganism occurred right in its optimal “comfort zone.” In other words, say the scientists, the bacterial enzymes aren’t affected by vagaries of the weather but are tuned to work most efficiently at the average temperature of their everyday habitat. This adaptation may protect them from potential ill effects stemming from swings in enzyme activity if things get too cool or too hot.
 
But what gives these enzymes the ability to function at their best in one temperature range or another? One of the bacteria the scientists tested was happiest when temperatures were in the moderate range; the other was a lover of intense heat. The puzzle was that the enzymes in the photosynthetic reaction centers of both are almost completely identical. Nonetheless, the scientists managed to find a tiny difference between them: Just two amino acids (the building blocks of proteins) were changed in the long protein sequence. As the French say: “Viva la difference!” When the scientists genetically engineered these proteins, replacing the two amino acids with their counterparts from the other bacteria, they saw a 10-degree change in the average temperature for peak enzyme activity, about the same as they found in the natural enzymes. This convinced them that the two tiny amino acids play a key role in setting the photosynthesis thermostat to either “lukewarm” or “tropical heat.” 
 
These findings, which appeared in Nature, may have future applications in a number of different fields. Crops, for instance, might be adapted to growing in extremely hot climates such as deserts. Enzymes used in industrial processes might be tweaked to work more efficiently. Scherz envisions another possible future use for the ability to control rates of photosynthesis: Plants grown for biofuel could be altered so as to produce greater biomass. These would absorb more than the usual amount of carbon dioxide from the atmosphere, thereby providing an environmentally friendly, renewable energy source and reducing a greenhouse gas, all at the same time.        
  
Prof. Avigdor Scherz's research is supported by the Charles W. and Tillie K. Lubin Center for Plant Biotechnology; the Avron-Wilstatter Minerva Center for Research in Photosynthesis; the Sylvia and Martin Snow Charitable Foundation; H. Thomas Beck, Toronto, Canada; Samuel T. Cramer, Beverly Hills, CA; Mr. and Mrs. Abraham Kahn, Mexico; and Mrs. Sharon Zuckerman, Toronto, Canada. Prof. Scherz is the incumbent of the Yadelle and Robert N. Sklare Professorial Chair in Biochemistry.  
 

In the Spotlight


  
Photosynthesis – the process of creating usable energy from sunlight and carbon dioxide – is the basis of all life on Earth. Photosynthetic organisms – plants, algae and some bacteria – feed all of the organisms higher up the food chain, supply the air with oxygen and help regulate the climate. But the real news is that many of these organisms, especially the higher plants, convert light to energy with an efficiency that human engineers can only dream of. 
 
Some of the  photosynthesis research at the Weizmann Institute explores such basic questions as how, even in dim light, the plant cell captures the solar energy it needs to function, while avoiding damage from overexposure in strong light. Meanwhile, the exploration of different aspects of photosynthesis has inspired a host of applications and new research avenues.
 
One of them is a method pioneered by Prof. Scherz and Prof. Yoram Salomon of the Biological Regulation Department that aims to destroy tumors by clotting their vascular supply, using light to activate a chlorophyll-based compound (chlorophyll being the green, light-absorbing substance in plants). This process, which takes advantage of the superb ability of chlorophyll to absorb light and generate radicals, is now in Phase II/III clinical trials for the treatment of localized prostate cancer.
(l-r) Oksana Shlyk-Kerner, Prof. Avigdor Scherz and Dr. David Kaftan. Peak reaction
Environment
English
  • Avigdor Scherz
  • Enzyme
  • Photosynthesis
  • Plant Sciences
  • Yoram Salomon

Everybody Needs a Friend Sometimes

English

Dr. Asaph Aharoni. The enemy of my enemy

 

 

We get by with a little help from our friends - but sometimes this help can come from an unexpected source. That’s what happened to a tiny relative of the mustard plant: Using genetic engineering, scientists endowed it with a strawberry gene, enabling it to recruit impressive numbers of "bodyguard" insects that attack the plant’s enemies. This is the first time genetic engineering has been used to devise plant protection involving natural bodyguards. Dr. Asaph Aharoni of the Weizmann Institute’s Plant Sciences Department, who performed this research with colleagues from the Netherlands, says the approach may help develop advanced environmentally friendly methods of pest control. "Instead of using large amounts of pesticides that pollute the soil and groundwater, we may enable the plants to recruit natural bodyguard insects that will protect them," says Aharoni.
 
Numerous plants in nature are capable of recruiting bodyguards via a chain process, which involves a slew of enzymes and culminates in the plant releasing a mixture of volatile organic materials, among them substances called terpenoids. Terpenoid-producing plants include corn, apple trees, beans, cucumbers, cotton and strawberries. They attract a wide variety of predator insects, such as ladybugs, which devour aphids, and parasitic wasps, which lay their eggs in the larvae of harmful bugs.
 
The pathway of terpenoid production and release is extremely complex, making it possible for the plants to generate different terpenoids to attract assorted insects for all sorts of purposes - from pollination to the repulsion of harmful bugs. But what happens when terpenoid production is ineffective and does not sufficiently protect the plant? Can the pathway be corrected to adjust the time, place and quantity of terpenoid release? Such a correction would significantly improve the plants’ ability to protect themselves against their enemies. The scientists studied this possibility in a model research plant called Arabidopsis thaliana, the first plant to have its entire genome mapped and deciphered.
 
In attempts to jump-start the terpenoid release system, scientists around the world have tried equipping the cells of different plants with a gene that codes for a unique enzyme responsible for terpenoid production. These experiments, however, failed to produce the desired results because the enzyme "chose" to work in a particular area of the plant cells that was lacking in sufficient raw materials to make terpenoids. To overcome this difficulty, Dr. Aharoni decided to insert into the Arabidopsis plant a single strawberry gene to which he attached a "routing" genetic segment. This segment directed the enzyme to a part of the cell that was rich in the required raw materials - a strategy that allowed the enzyme to step up terpenoid production.
 
The engineered plant released large quantities - 25 times more than the natural plant - of a signaling chemical that recruits predator mites. At this stage, the scientists decided to test the effectiveness of the method. Predator mites were allowed to roam freely and choose between a genetically engineered and a regular plant. The result: On average, 388 mites rushed to the engineered plant, while only 191 flew over to the regular plant. These results were recently published in the journal Science.
 
Unlike natural plants, which produce terpenoids only on demand, the engineered plant releases the signaling chemical continuously, so that it cries "Wolf!" even when it’s not being attacked. This never-ending alert could conceivably create a problem, as predator mites have occasionally been known to become disappointed and lose their "trust" in the help-recruiting signals. To prevent this undesirable situation, the scientists are currently striving to engineer plants in which it will be possible to control when the signaling substances are released.
  
Dr. Asaph Aharoni's research is supported by the Sir Charles Clore Research Prize; the Henry S. and Anne Reich Family Foundation; Sir Harry Djanogly, CBE; and Mr. and Mrs. Mordechai Segal, Israel. Dr. Aharoni is the incumbent of the Adolpho and Evelyn Blum Career Development Chair of Cancer Research.
 

Predatory mite (r) attacking a plant-eating insect. Photo: Koppert Biological Systems, the Netherlands

 

Dr. Asaph Aharoni. Strawberry defense
Environment
English
  • Asaph Aharoni
  • Genetic engineering
  • Plant Genetics
  • Plant Sciences

In Sync with the Sun

English
The great 18th-century botanist Carl Linnaeus is said to have planted a 'timekeeping' garden in which he could tell the hours of the day by the opening and closing of various flowers. Like Linnaeus' flowers, most plants and animals have internal biological clocks called 'circadian rhythms,' which synchronize daily activities such as awakening or petal spreading.
 
Prof. Meir Edelman of the Plant Sciences Department, working with Dr. Autar Mattoo of the USDA Agricultural Research Service in Maryland, has recently found that a 24-hour circadian clock regulates the most basic function in plants -  photosynthesis (the process in which plants produce sugar and oxygen -  see box).
 
Edelman and Mattoo have been collaborating on studies of photosynthesis for over 20 years, ever since Mattoo arrived at Edelman's lab from India for a two- year stint as a guest researcher. Since that time, their research has focused on an unusual protein central to photosynthesis.

 

Prof. Meir Edelman. Daily rhythm
 
The protein, called D1, sits right at the heart of the plant's energy centers, and is the dynamo of the photosynthetic process. Edelman and Mattoo were intrigued by their finding that a phosphate molecule regularly binds to, and is later released from, D1. They demonstrated that this process (called phosphorylation) does not occur at a steady rate; rather, its magnitude rises and falls in a 24-hour cycle. This swing between peak and ebb met all of the criteria for circadian rhythms: It continued for several days even when night and day cycles were artificially interrupted in the lab, and the cycle could be reset -  just as the body of a person traveling across different time zones resets its sleep cycle after a few days. (The cycle did break down, however, when plants were kept in total darkness, as photosynthesis cannot take place without light.)
 
Interestingly, they saw that the high point of this cycle did not coincide with the time of peak sunlight. Instead, phosphorylation climaxed at about 10 a.m., several hours before high noon, and afterward began to drop off sharply. This meshed in with the scientists' belief that D1 acts as a 'light meter' for the plant's energy centers. The scientists theorize that the phosphorylation cycle may be timed to help plants protect themselves against a sunlight 'overdose': Although the plant depends on sunlight for nourishment, too much sunlight can damage plant cells. D1 is tuned to work in a wide range of light conditions, including the weak light of early morning and cloudy days. But when the intensity of the light passes a certain level, the system has more incoming energy than it can handle. To prevent overload, the plants must suppress the reaction.
 
Continuing their research into the mystery of circadian rhythmic control of the D1 protein, Edelman and Mattoo have isolated an enzyme they suspect may be the main agent of daily D1 phosphorylation. Now they are performing further experiments using this enzyme to see if it is, indeed, the mainspring of the photosynthesis clock.

Illustration: plants In Sync with the Sun

From sunlight to sugar

Photosynthesis is the process in which green plants and certain other organisms produce carbohydrates using light, water and carbon dioxide. The green pigment in plants (chlorophyll) collects energy from sunlight.

 
The plant then uses the sunlight to split water into hydrogen and oxygen. The oxygen is released to the atmosphere as a byproduct, while the hydrogen adheres to molecules of carbon dioxide that the plant has soaked up from the air, producing sugar. D1, the protein studied by Edelman, plays a central role in this process, using the collected energy to split water.
 
 
Prof. Edelman's research was supported by the Avron-Wilstaetter Minerva Center for Research in Photosynthesis. He is the incumbent of the Sir Siegmund Warburg Chair of Agricultural Molecular Biology.
 
 
Illustration: plants In Sync with the Sun
Environment
English
  • Circadian clock›Circadian clock
  • Meir Edelman
  • Photosynthesis
  • Plant Sciences

Higher Yields, Lower Pollution

English
 
Like miniature samurai, some species of fungi carry around an arsenal of personal weapons for use in overcoming assaults against the plants they are sworn to protect. Plants, like prosperous lords, grow faster and more luxuriantly when a member of the fungus genus Trichoderma is nearby. The fungal weapons, which include the biological, chemical and conventional, have made this group of fungi a favorite agent of biological plant disease control over the last decade.
 
Many fungi are known to attack plants. However, Trichoderma curiously sides with the plants, raising the possibility of "fighting fungus with fungus" instead of using pesticides (which are dangerous to humans and harmful to the environment).
 
Found in soil all over the world, Trichoderma is known to latch on to harmful fungi that attack plants and destroy them. By using specialized tools, Trichoderma coils around the body of the invading fungus and penetrates its outer cell walls using several enzymes, including potent chitin-eating enzymes called chitinases. (Chitin is the hard material found in the shells of beetles and crabs as well as in the cell walls of most fungi.)
 
Work in the lab of Prof. Ilan Chet, President of the Weizmann Institute, focuses on this important fungus and the chitinase genes that make it such a powerhouse of plant defense. Chet began his work on Trichoderma at the Hebrew University of Jerusalem, where he discovered two out of five versions of chitinase known to exist in Trichoderma. Each version is encoded by a different gene; and each gene is programmed to switch on in response to a different set of stimuli.
 
Today, at the Weizmann Institute's Biological Chemistry Department, he has isolated and sequenced a previously unknown gene responsible for producing a key chitinase enzyme, in research performed with team member Dr. Ada Viterbo, Prof. Aviv Zilberstein and Dr. Smadar Penini of Tel Aviv University, as well as scientists from the Hebrew University's Faculty of Agriculture. Chet's team then set out to determine what it takes to "turn on" the gene -  that is, produce the enzyme.
 

Remote sensing

 
The strongest stimulus they found for firing up chitinase production came from the presence of chitin in the cell walls of nearby, harmful fungi. This particular chitinase gene begins producing its cell-wall-eating enzyme even before there is physical contact between Trichoderma and the attacking fungus. The gene appears to use a remote sensing mechanism that detects foreign chitin by picking up on tiny molecules that the attacking fungus releases into the surrounding medium.
 
Other stresses, such as low levels of available nutrients and temperature extremes, can also trigger chitinase production.
 
The team also showed that when chitanase works in tandem with other, similar enzymes, a synergistic effect ensues, providing augmented firepower against invaders.
 

Early warning system

 
Trichoderma not only acts as a biocontrol agent -  it also functions as an extra helping of fertilizer. In the latest research to come out of the Weizmann Institute Trichoderma lab, Chet and postdoctoral fellows Michal Shoresh and Iris Yedidya have shown why this happens.
 
Trichoderma works its way through the outer layers of the plant's root tissue and into the spaces between cells, where it remains without injuring the plant. The researchers found that the plant responds by activating a part of its immune system. It thus seems that Trichoderma acts as a kind of "early warning" system, putting the plant on high alert and improving its readiness to deal with an actual attack. Plants hosting Trichoderma had quicker response times to onslaughts of harmful bacteria in any part of the plant and were able to defeat the invading microbes more easily. Because Trichoderma-inoculated plants are better equipped to ward off infection, they are free to devote more of their energy to growth.
 
The researchers noted a number of chemical changes in the leaves, indicating that signals are relayed systematically up the plant from the roots, triggering a coordinated chain of responses on the way. By analyzing the pattern of chemical changes, they determined that a specific defense mechanism, known as "induced systemic resistance," had been activated in the plant.
 
Once the weapons used by Trichoderma are understood, the knowledge can be applied in several ways. Current disease control methods that employ the fungus can be improved. In addition, the genes that carry the instructions for the weapons' manufacture are now being engineered for other organisms -  such as bacteria grown specifically for assorted pesticide applications or plants that will carry the disease resistance traits themselves.
 

A slow release

 
Friendly bacteria or fungi used in biocontrol agents are especially susceptible to the sun's ultraviolet rays and can also be destroyed by micro-organisms in the soil. Prof. Ilan Chet, together with Prof. Amos Nussinovitch of the Hebrew University's Faculty of Agriculture and doctoral student Cheinat Zohar-Perez, recently developed a "time-release" system that keeps the helpful microorganisms safe while allowing steady amounts of their disease-fighting enzymes to reach the plants.
 
In a trial conducted in cucumber plants, the spread of disease dropped by 80 percent. The system is based on the creation of tiny beads, some no more than a few microns in size,which are made from a water soluble polymer. Inside each bead, the scientists trap roughly a billion friendly bacteria or fungal spores along with enough nutrients to sustain them over time. Thus, the bacteria and fungal spores are able to continue producing enzymes that attack various disease-causing microorganisms.
 
The ecologically safe, biodegradable polymer breaks down over time, slowly releasing the microorganisms into the soil.
Options for producing the beads on a commercial basis are currently being explored.
 

Got the greenhouse blues

 
Greenhouses are ideal breeding grounds for many kinds of plant diseases, including fungal infections. High humidity and other greenhouse conditions contribute to the problem. Chemical applications are problematic, as workers are constantly exposed to the air and soil, and the chemicals often break down more slowly in the closed greenhouses. In addition, some fungal infections do not respond to known chemical pesticides, while others become resistant to particular chemicals over time.
 
For these reasons, biocontrol products, such as Trichoderma-based preparations, have made important inroads into the greenhouse market, especially for growers raising vulnerable seedlings. Thanks to Chet and his years of work on Trichoderma, Israel is a world leader in research and development of these products.
 
Outside the greenhouse, the demand is mounting for biological control methods as awareness of the risks of pesticides to consumers and the environment grows. For instance, production of one widely used chemical for control of fungal disease in soil, methyl bromide, will be banned world-wide in 2005 under the Rio Convention because it destroys the ozone layer. Therefore, developing resistant plants and creating biocontrol applications that can be used efficiently on all kinds of field crops are of the utmost importance.
 
Prof. Chet's research was supported by Myrna Strelinger, Tucson, AZ.
Environment
English
  • Immune system
  • Plant Sciences
  • Plant disease

For the Love of Wheat

English

Khalil Kashkush, Profs. Avi Levy and Moshe Feldman. Wheat enthusiasts

Three Israelis from different generations and backgrounds – one a former kibbutznik, the other from France and the third from an Arab village – all wanted to be agronomists yet fell in the love with the science of wheat.
 
As a member of Kibbutz Mishmar David in the 1950s, Prof. Moshe Feldman spent his days helping to plant and harvest the kibbutz’s 4,000 dunams of crops. From his early childhood he had loved nature: “Becoming an agronomist was the natural choice,” he says. But after a year’s study in Jerusalem, he was drawn to biology, particularly its evolutionary aspects. After completing his postdoctoral studies, in the course of which he had the opportunity to work with world-renowned wheat scientist Ernest R. Sears, he came to the Weizmann Institute in 1969 to continue probing the secret to wheat’s enormous success as an adapter: It has flourished all over the world, whether in the Brazilian tropics, the semi-arid areas of Sudan or underneath Canadian snow. “Wheat laid the foundation for civilization as we know it,” says Feldman. “Having learned to cultivate wheat, humans were able to settle in one place for long periods of time, building villages and towns. The wild wheat species that humans first cultivated – ‘the mother of all wheat’ – was discovered in Israel and still grows in these parts.”
 
About a decade later, along came a student, now Prof. Avi Levy, who shared Feldman’s fascination with wheat. He had made aliyah from France at the age of 17 and sought to realize the Zionist dream to its fullest – to work in agriculture in the land of Israel. “My mother cried when she heard I wasn’t going to be a doctor,” he says. He, too, began studying agriculture but became absorbed in wheat genetics. “Wheat is a small, beautiful, modest plant, with very few needs,” says Levy, “and yet its genetics is extremely complex.” He began his doctoral studies at Weizmann under Feldman, whose research in wheat genetics and evolution was by then well known. After completing his postdoctoral work in Stanford, he returned to the Institute as an independent researcher, inspired by Feldman to continue in this field. “But I had to prove that I wasn’t just continuing Mossik’s [Moshe’s nickname] ideas,” he says jokingly. So he branched off to a new topic, the dynamics of genes in other species. “Fortunately, my research proved in time to be central to wheat studies,” he says, and the door reopened to his favorite organism.
 
About four years ago, another wheat enthusiast joined their ranks – graduate student Khalil Kashkush. “When I was born, the first things I saw were strawberries, flowers and wheat,” he says, referring to the produce on his father’s farm in the Arab village of Qalansuwa. The crops’ dependence on rain had made him dream as a young child that one day he would devise a strain of wheat that needed no water. He decided to become an agronomist. “Like Avi’s mother, mine also wanted me to be a doctor. Now she consoles herself that at least I’ll have the title ‘Dr.’,” he laughs. His studies continually leave him feeling that he doesn’t know enough – and so, agronomist dream deferred, he is now completing his doctoral degree in the plant sciences. His work with advisors Feldman and Levy has already led to the publication of three articles in major scientific journals. “Khalil has a lot of spirit and the courage to do things that others before him haven’t done,” says Feldman. “We have high hopes for him. He is going to a leading laboratory to do his postdoctoral work and if he proves himself there, he’ll have an open ticket to all research centers.” Levy adds: “The future will tell, but Moshe, an inspiring teacher, might have laid the foundation for a dynasty of wheat geneticists at the Weizmann Institute of Science.”
 

Wheat and Human Evolution

 

Wheat might hold clues to one of the most mystifying questions in human evolution: Did a primitive creature double its genome around 500 million years ago, creating the genomic leap that led to the creation of all mammals?  
 
Wheat has doubled its genome several times in the past, creating new species of wheat virtually overnight. “Genomic doubling can be easily induced in the lab when it comes to wheat,” says Levy, “which is why it might provide insight into one of the events that might have shaped the human genome.”
 
Though for many years considered an exotic feature of plants, genome doubling is today recognized as a widespread force that has influenced the evolution of the animal, plant and fungi kingdoms. But human evolution? Scientists have found that many duplicated segments in the human genome date back to approximately 500 million years ago, suggesting that a whole genome duplication event may have occurred at that time. Yet this sort of “genetic archaeology” has its obstacles: Genes change over time and what could have begun as the perfect duplication of a gene might have altered over millions of years. Studying wheat could help scientists visualize what our genome would look like today if such a doubling event had indeed taken place in our past.
 
The team has uncovered several events that occur after genomic doubling. One finding was recently published in Nature Genetics. Doubling of genetic information was known to cause “genomic shock.” Genes that are normally dormant wake up and start interfering with the normal function of other genes. These genes are called “jumping genes” because they move around the DNA, “stepping on” other genes. What wasn’t known was that jumping genes have much subtler ways of sowing confusion: “Even when they don’t jump, they can turn neighboring genes on and off, reversing their activity,” says Levy. Since the publication of their article they have received reactions from many scientists who believe that the same kind of phenomenon occurs in human cells, which also contain many jumping genes.
 
The genome of wheat as we know it today is actually an amalgam of several wheat species, whose genomes can serve as genetic backup systems. The extra gene copies in the “backup genomes” come into play if some genes become mutated.  
 
If one of the primitive creatures serving as our distant forefathers doubled its genome, the extra gene copies, or “backup systems,” might have been used as playdough for creating new functions. Feldman: “The sudden increase in genetic information together with tolerance to mutations might have led to the creation of new genes, increased genetic complexity and, gradually, to the development of more sophisticated species.”  
 
Prof. Moshe Feldman is the incumbent of the Marshall and Edith Korshak Professorial Chair of Plant Cyto-genetics. His research is supported by the Charles W. and Tillie K. Lubin Center for Plant Biotechnology.
 
Prof. Avraham Levy’s research is supported by the Raymond Burton Plant Genome Research Fund and the Charles W. and Tillie K. Lubin Center for Plant Biotechnology.
Environment
English
  • Avi Levy›Avi Levy
  • Moshe Feldman
  • Plant Genetics
  • Plant Sciences

Uprooting Hunger in Africa

English

Experimental field has triple yield

 
A slender purple flower is a leading cause of the ever-rising death toll in Africa due to starvation. Appropriately named "witchweed,"it feasts on more than 70 percent of all corn crops in Kenya alone. A recently reported method for killing witchweed may be able to rescue this staple of the African diet from parasitic destruction.

"Witchweed attaches itself to the crop's roots,"says Prof. Jonathan Gressel of the Weizmann Institute of Science's Plant Sciences Department, "then drains it of life." The innovative method of attacking witchweed, conceived by Gressel and developed in collaboration with researchers at CIMMYT (the Spanish acronym for the International Maize and Wheat Improvement Center), kills the colorful weed in its early stages of growth. That is the key to its success.

Until now, African farmers commonly removed witchweed (Striga hermonthica) by hand, but by the time it emerged above ground it had already done its damage. Herbicides applied after its emergence were also ineffective for the same reason.

Gressel decided to test whether coating the corn seeds with herbicide before planting would have an effect. The result: When the seeds sprouted, the parasite unwittingly devoured the weed-killing chemical from the crop's roots or surrounding soil and died. By the time the crop ripened, the herbicide, applied at less than one-tenth the usual rate, had disappeared, leaving the corn unaffected.

Tested in four African countries over ten crop seasons, the technique has on average tripled corn harvests and dramatically cut the cost of growing this crop, sparing farmers the expensive process of air-spraying entire fields. In addition to saving lives, this method may be an economic blessing to Africa: Yields lost to witchweed are valued at approximately $1 billion annually.

For the method to work, the seed itself must be resistant to the herbicides. Gressel sought out strains of corn that resist these herbicides and found one in the United States. His African colleagues Drs. Alpha Diallo and Stephen Mugo crossbred those seeds, provided by Pioneer International, Inc., with local corn to endow them with resistance to other African afflictions as well. The seed treatment technology was perfected by Drs. Fred Kanampiu and Dennis Friesen.

The new technology was presented at a conference in Kenya in July. After viewing the results in the field, Kenyan authorities pledged to fast-track approval for the method.
 
Prof. Gressel's research is supported by the Virginia Polytechnic Institute; Mr. David M. Safer, San Francisco, CA; and the Charles W. and Tillie K. Lubin Center for Plant Biotechnology. He holds the Gilbert de Botton Chair of Plant Sciences.
 
  • According to UN figures, as many as 24,000 people die every day of starvation around the world. This devastation is substantially concentrated in Africa.

​

  • Since the beginning of 2002, the U.S. Government, by far the leading food donor to Africa, has provided more than $68 million in emergency humanitarian aid and plans to provide an additional $82 million by the year's end.
Kenyan farmer in an experimental corn field
Environment
English
  • Genetic engineering
  • Jonathan Gressel
  • Plant Sciences
  • Witchweed
Yes

A Plant's Brainy Balancing Act

English

Prof. Gad Galili. Like corn, like human


Plants don't have a brain. True, they have other winning traits - like the ability to withstand searing summer skies or biting frost (they can't pack up and leave when times get rough). Nevertheless, they lack the neuron-based information processing found in animals, from the single-neuron system found in sea anemones and hydras to the remarkably complex human brain.


Surprisingly, however, what started out for Prof. Gad Galili as a quest to create more nutritious, hardier crops has detoured into research findings that offer a better understanding of the molecules underlying brain function and of a severe human genetic disorder resulting in mental retardation.


A geneticist in the Weizmann Institute's Department of Plant Sciences, Galili focuses on the biochemical machinery that churns out lysine - an amino acid charged with overseeing plant growth and development that is also an essential amino acid in humans, where it serves as a building block of proteins and is vital for proper growth and bone development. Since humans are unable to synthesize lysine they must receive it through their diet, yet cereals and other important crops produce this nutrient in only very small amounts, a fact that is largely responsible for the malnutrition plaguing developing countries and the need to supplement livestock feed with costly additives.


Hoping to boost plant lysine levels, Galili's team began by piecing together the players along this biochemical pathway, asking which compounds are involved and how they interact. They succeeded in pinpointing a key enzyme, known as DHPS, which regulates lysine production. 'The plant doesn't waste any energy,' says Galili. 'Once lysine is present in sufficient amounts, it 'switches off' the DHPS enzyme - a process known as feedback inhibition - preventing further lysine production.' When looking around to see how other organisms tackle this challenge, the team uncovered a counterpart enzyme in bacteria that is less sensitive to feedback inhibition. They decided to genetically insert the gene encoding this bacterial enzyme into a model plant. The result - a significant increase in lysine levels - is currently being used to improve soybean, maize, and canola.

The tightrope walk

But then some of these plants threw a curveball; they started breaking down the extra lysine. It turned out that lysine accumulation consists of both an anabolic, lysine-producing track and a catabolic track, where lysine is broken down into glutamate. The engineered plants were breaking lysine down because excess levels are toxic to the plant. 'It soon became clear that the lysine-glutamate pathway is a master of self-regulation, constituting one of the most highly regulated plant biochemical pathways known,' says Galili. He and others discovered that plants normally maintain the lysine levels needed for protein-based growth and 'housekeeping chores,' while also breaking it down to produce moderate amounts of glutamate. But when under stress, the plant's catabolic machinery switches into overdrive, breaking down far more lysine into glutamate, which is then further modified to produce stress-resistance compounds.


Zeroing in on this catabolic track, Galili has isolated a key gene, known as LKR-SDH, which is equipped with unique regulatory features that may enable lysine catabolism to flow at a slow or rapid pace according to environmental conditions. His findings led to the identification of a counterpart gene in humans that also mediates the production of glutamate (in this context a neurotransmitter playing an essential role in learning, memory, and a host of other tasks - see box). The human gene also keeps lysine levels in check to enable normal brain function. In fact, in April 2000 a team led by Michael Geraghty at the Johns Hopkins University School of Medicine discovered that this gene is mutated in patients with hyperlisinemia, a genetic disorder resulting in mental retardation and other symptoms. 'The discovery of similar catabolic genes in plants and in humans places us in a unique position,' says Galili. 'Studies of this pathway in plants may help reveal how lysine contributes to glutamate production in the brain.'

Nerve Talk

Nerves talk to one another through neurotransmitters - chemical compounds that cross a bridge to neighboring neurons, where they bind to matching receptors. This explains why a recent discovery by a New York University team that plants have receptors for the glutamate neurotransmitter sent ripples of excitement through the scientific community. Researchers had initially thought that plants produce glutamate to protect themselves from herbivores. Indeed, in what may have evolved as a defense strategy, glutamate and many other plant compounds affect human and other mammalian nervous systems, producing a range of hallucinogenic, anesthetic, and other reactions.


However, the discovery of plant receptors for glutamate has triggered an enticing new idea - that similar to its role in humans, glutamate may act as a signaling molecule in plants, conveying information about the environment or regulating developmental processes. In other words, it may underlie an ancient signaling mechanism that has made its way up the evolutionary ladder.

Potential Fields

Personable and brimming with energy, Prof. Gad Galili clearly loves his job. 'When I look at an agricultural field, I see potential,' he confesses. 'My passion is basic science, to understand the mechanisms behind plant function and survival; but I'm also fascinated by implementation, to see how plants can be designed for better nutrition.' Galili believes that future research should include the development of crops with boosted medicinal properties such as antioxidant-rich tomatoes for heart disease patients or for slowing down aging and fighting cancer. Currently collaborating with diverse research teams, including those of Csaba Koncz and Rainer Hoefgen at Germany's Max-Planck Institutes, one of Galili's primary goals is to fine-tune the plant lysine-glutamate pathway, turning off its catabolic machinery at a critical window in time during seed development.


Prof. Galili holds the Bronfman Chair of Plant Science. His research is supported by the Minna James Heineman Stiftung, the Raymund Burton Fund for Plant Genome Research, the Harry and Jeanette Weinberg Center for Plant Molecular Genetics Research, and the Avron-Willstaetter Center for Photosynthesis Research.

 

Prof. Gad Galili.
Environment
English
  • Brain
  • Gad Galili
  • Gene regulation
  • Genetic engineering
  • Plant Sciences

Playing the Odds

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Prof. Avi Levy and Vera Gorbunova: DNA repair and evolution
 
Rapid evolution is crucial for plants, embroiled as they are in a race for survival against formidable armies of fungi and bacteria.
 
"Plants evolve far more rapidly than mammals," says Prof. Avi Levy of the Weizmann Institute's Plant Sciences Department. "In the last 300 million years, only 4,000 mammalian species have evolved, in contrast to nearly 200,000 flowering plant species exhibiting a plethora of shapes, colors, and adaptations." Plants also demonstrate much greater variation than mammals in the amount of DNA per species. This genomic plasticity may be the plant's answer to a main grievance: unlike mammals, plants cannot flee in the face of danger; they have no choice but to stand their ground.
 
Levy and doctoral student Vera Gorbunova are investigating the underlying mechanisms that enable plants to be so versatile. They have found that compared to mammals, plants are highly prone to making "mistakes" when repairing damaged DNA. According to Levy and Gorbunova, the plant's error-prone repair strategies may actually be a blessing in disguise -- driving evolution forward by enhancing genetic variability.
 
"Plants tend to 'improvise'," says Gorbunova. "While their repair mechanisms seal a tear in the DNA, as do those of mammals and yeast, plants often 'rewrite' or 'delete' parts of the DNA in the process. The 'repaired' DNA is rarely identical to the original."
 
Genetic mutations occur regularly in all organisms as a result of environmental factors, including ultraviolet radiation and chemical toxins as well as, on a smaller scale, natural cell processes. Plant mutations are also influenced by jumping genes: during cell division these natural trailblazers are capable of jumping along the plant's DNA, randomly "knocking out" genes. Collectively, these mutagenic factors leave chaos in their wake, tearing the DNA and scrambling and deleting the genetic "letters" encoding an organism's traits.
 
Damaged DNA, if not repaired, can have disastrous consequences, especially in organisms that can develop cancer as a result. In plants, mutations can accumulate without the danger of their leading to cancer, since cells do not move within the plant body.
 
Fortunately, all organisms employ emergency repair "crews" designed to reverse or mitigate mutation-induced damage. Weizmann scientists have discovered that the mutation repair systems in plants are highly error-prone. In roughly 70% of cases, plants will simply "paste" torn DNA ends together, using a biological Scotch tape repair enzyme known as DNA ligase. This unsophisticated technique does not take into account the numerous complications that can occur.
 
"Unlike a precise cut made by scissors, DNA breaks generally result in the loss of entire pieces," says Gorbunova. In addition, exposed DNA ends are immediately scouted out and attacked by degrading enzymes. Therefore, simple rejoining via ligation generally leads to scrambling of the genetic code or loss of information.
 
Most interestingly, Levy and Gorbunova found that plants even "stitch" together diverse DNA from multiple sources. An apt analogy: Faced with a disastrous tear in their favorite jeans, plants generally sew the edges together; or they go for a dramatic fashion statement, introducing a different fabric or even a multicolored patchwork. In contrast, yeast takes the conservative route, replacing the missing fabric with identical material, Levy explains. Yeast does so by going to a homologous chromosome (genetic information is usually organized in pairs, termed homologous chromosomes, with one member of each pair originating from the female parent and the other from the male). According to the Weizmann team, when DNA in yeast is damaged, missing fragments are obtained by invading the homologous "partner" and copying an identical sequence. Plants also employ this strategy. But instead of choosing the problem-free homologous repair route, they commonly invade a nonidentical chromosome, leading to the insertion of unrelated DNA sequences.
 
Plants are wonders of evolution
 
 
These new insights into mutation repair pathways may lead to breakthrough genetic engineering efforts. "Today, it is nearly impossible to target a specific gene in order to effectively integrate beneficial traits into the plant genome," says Levy. "With yeast, in contrast, the 'designer' gene inserts itself directly into a homologous target." One prevailing idea is to introduce "blinders" into DNA modification pathways by "knocking out" or inhibiting the genes involved in non-homologous repair. "In this scenario, the DNA would have to use the alternative homologous machinery - thereby enabling precise integration and effective expression of beneficial traits."
 
"This phenomenon may provide a telling example of how error-prone DNA repair can generate useful traits," says Levy. The inherent approach is to absorb the loss of "bad" mutations -- an inevitable by-product of error-prone repair, so as to receive the "good" adaptability-enhancing sequences. The overriding strategy of plants for overcoming the problem of immobility may read as follows: become "star athletes" in the evolutionary race instead.
 
Environment
English
  • Avi Levy›Avi Levy
  • DNA damage and repair›DNA repair
  • Mutation
  • Plant Sciences

Closing the Technology Gap

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Prof. Robert Fluhr. Removing the bottleneck to transgenic crops


Virus-resistant barley, herbicide-tolerant rice and slow-to-ripen tomatoes -- these upgraded staples are among the now familiar products of the age of genetic engineering. The march of new transgenic foods to the supermarket shelves depends on closing the gap between plant research at academic institutions and the technologies available to plant breeders.

The Israel Ministry of Science's new national Plant Genome project at the Weizmann Institute intends to bridge this gap -- and put Israel on the map of plant genome efforts worldwide.

According to its coordinator, Prof. Robert Fluhr of the Institute's Plant Genetics Department, the project aims at removing the main "bottleneck" blocking the development of new transgenic crops: the isolation and characterization of genes. It offers seed companies and plant breeders the much-needed research technologies and expertise that will enable them to produce plants with higher nutritional value, better resistance to disease and other much desired properties.

Funded by the Ministry of Science, the Plant Genome project involves scientists from three research institutions: the Weizmann Institute, the Hebrew University of Jerusalem and the Technion-Israel Institute of Technology.

The project's activities encompass a variety of undertakings involving academics, scientists in industry and plant breeders across Israel. Possible joint research with the neighboring Arab countries is also under consideration. "Agriculture has always been Israel's first bridge to international relations," says Fluhr.

Current activities in Israel include studying genes affecting leaf shape (a characteristic that enables plants to adjust to specific climatic conditions), endowing tomatoes with resistance to various diseases, and producing more color varieties in tomatoes and other plants.

The project offers plant breeders a precise genetic map of the tomato, "libraries" that contain plant genes and the technologies to introduce foreign genes into plant cells. In addition, the project offers access to unique research tools, such as the pencil-sized mini-tomato plant that carries the so-called "jumping genes." These genes "jump" along chromosomes, causing mutations, such as different colors and shapes of leaves and fruit, and can be used to isolate genes with specific functions. The mini-tomato's diminutive size turns a greenhouse into the research equivalent of a several-acre field.

Moreover, since plant and human genes are built of the same chemical constituents, the project benefits from resources and facilities available through the Institute's Human Genome Project. In particular, these include a strong bioinformatics infrastructure -- namely, the gene sequencing facilities as well as powerful computers and on-line connections that provide scientists and industries with access to daily updated, international gene data bases. The Institute's bioinformatics interface is also used to compile all the data generated within the project itself, making it available to researchers seeking to produce better crops in Israel and worldwide.
Environment
English
  • Gene code
  • Plant Genetics
  • Robert Fluhr
  • Tomato

Sun-Protection Mechanism of Plants Unraveled

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Prof. Zamir. Secrets of sun-resistance

 
Agricultural crops resistant to strong sunlight may one day be cultivated in the hottest and most drought-ridden parts of the world thanks to recent finding of Weizmann Institute researchers.

The scientists have unraveled the protective mechanism allowing a particularly sturdy salt-water alga, Dunaliella bardawil, to thrive in scorching sunlight. In the future, it may be possible to manipulate a similar mechanism existing in higher plants, including crop, in order to enhance their resistance to the sun, according to Prof. Ada Zamir of the Institute's Department of Biochemistry. She deciphered the mechanism together with department members Haim Levy, Tamar Tal, Dr. Aviv Shaish, Dr. Irena Gokhman and Dr. Amnon Lers.

Dunaliella bardawil is known for its legendary resistance to the salt and sun, which allows it to thrive in the brackish marshes of the Sinai desert and even in the Dead Sea. It was first isolated from the Bardawil marsh in Sinai and studied by the late Institute Professor Mordhay Avron, together with his then student, Prof. Ami Ben-Amotz.

The dunaliella alga fascinates scientists because it is both a remarkable survivor and functionally very similar to higher plants. These two properties make it an excellent model for studying survival strategies that may be relevant for growing useful crops under harsh conditions, according to Prof. Zamir.

Excessive sunlight causes most plants to produce toxic oxygen molecules that damage and eventually destroy the plant's photosynthetic machinery. Zamir and her associates have discovered a protein, now known as Cbr, that is formed in dunaliella whenever this machinery is threatened. Using genetic engineering, the researchers have cloned the gene coding for this protein.

They further observed a close link between Cbr and a carotenoid pigment called zeaxanthin, also formed under the stressful conditions of intense light. The scientists have concluded that the protein binds with the pigment to form a light-protective "antenna" or "lightening rod," which diverts the excessive, harmful light from the sensitive components of the photosynthetic machinery. While producing Cbr and zeaxanthin, the alga also forms large quantities of beta-carotene, an orange pigment that serves as the plant's natural sunscreen.

Prof. Zamir holds the Carl and Dorothy Bennett Chair of Biochemistry.

The research was supported by grants from the Minerva and the German-Israel Foundations.
 
Environment
English
  • Ada Zamir
  • Alga
  • Dead Sea
  • Genetic engineering
  • Plant Sciences

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