Banana yellow, lime green, plum purple: Our first association with a fruit is often its enticing color. But for plants, color is about much more than aesthetics. The purple compounds in grape skins, for instance, protect the fruits from ultraviolet radiation, pests and diseases. Humans also benefit from eating these substances – known as flavonoids – as they have all sorts of antioxidant and disease-preventing properties. They not only improve our health; these compounds and their derivatives tempt us into eating the fruit by helping it develop a pleasing aroma when it ripens.
Mutations in genes for color are prized – they produce purple peppers, yellow watermelons, pink tomatoes. Pink tomatoes lack a yellow pigment that’s found in normal red tomato skins. They’re also a bit sweeter than the average red tomato, making them popular, especially in the Far East. For this reason, breeders and agricultural firms have taken an interest in them.
Pink tomatoes have also caught the attention of Dr. Asaph Aharoni of the Institute’s Plant Sciences Department. Aharoni and his team focus on the thin outer layer of a plant – the cuticle – which is mainly composed of fatty, wax-like substances. In tomatoes, these substances are joined by large amounts of flavonoids, which both help to protect the fruit and add a strong yellow tint to the color. The cuticle of the mutant tomato, in contrast, is a delicate, translucent pink. In research that appeared in PLoS Genetics, Aharoni, Drs. Avital Adato and Ilana Rogachev, and research student Tal Mendel discovered the gene that makes the regular tomato yellowish-red and the mutant tomato pink.
Aharoni’s lab has a system that’s unique in Israel, and one of only a few in the world. Using a combination of molecular, chemical and analytical methods, he and his research team are able to identify hundreds of metabolites – active compounds in plants – and create a comprehensive profile of all the substances produced in the mutant plant, which is then compared with that of normal plants.
The scientists found that the difference between pink and red tomatoes goes much deeper than an absence of yellow pigment in the skin: They identified around 400 genes whose activities were radically different in the mutants – at least twice as intense or less than half of normal. The mutation influenced the production of a number of substances in the flavonoid family, both in the cuticle and in the flesh of the fruit. In addition, pink tomatoes contain less lycopene – a red pigment and powerful antioxidant known to have a number of health benefits. The pink cuticle is thinner than the red one but less flexible, due to alterations in the composition of the fatty substances.
The gene mutated in the pink tomato, known as SIMYB12, is a sort of “master switch” that regulates an entire network of other genes, overseeing the production and quantities of many metabolites in the tomato fruit. Aharoni: “Researchers can now use this gene as a ‘marker’ to reveal the future color of the fruit early on – months before the plant flowers and bears fruit. This might greatly accelerate the creation of new varieties, a process that normally can take 10 years or more.”
Dr. Asaph Aharoni’s research is supported by the De Benedetti Foundation-Cherasco 1547; and the Willner Family Foundation. Dr. Aharoni is the incumbent of the Adolpho and Evelyn Blum Career Development Chair of Cancer Research.
Color It Mellow
The rabbis who wrote the Talmud around 1,500 years ago knew about the unique properties of frankincense (levona in Hebrew). They sanctioned adding a pinch of the aromatic tree resin to the wine of a condemned criminal, to “benumb his senses.” Research by Dr. Arieh Moussaieff, a postdoctoral fellow in Dr. Asaph Aharoni’s lab, shows that this resin, gathered for thousands of years from trees of the genus Boswellia, contains compounds that relieve depression and anxiety.
Moussaieff first encountered frankincense while researching a plant-based remedy made in a monastery in Jerusalem’s Old City. In folk medicine, the resin is believed to have anti-inflammatory properties, and to ease digestive and respiratory problems. But frankincense is most widely used as incense in religious ceremonies ranging from ancient Egyptian, Jewish and Christian rites to Chinese and Indian rituals.
In his doctoral work at the Hebrew University of Jerusalem, Moussaieff isolated the active compounds in the resin. When tested on mouse models of human head injury, he found that some of these substances provide protection for the nervous system. He later noted the resin’s antidepression and antianxiety properties and, investigating further, found that they act on a previously unknown pathway in the brain that regulates emotion. These findings not only help explain the ubiquity of frankincense in religion, they also hint that the active compounds might be used in the future to treat any number of neurological diseases, from Alzheimer’s and Parkinson’s to depression.
Moussaieff’s current research involves investigating how the resin is produced in the tree. The active compounds are, at present, too complex to manufacture on a marketable scale, and he hopes that uncovering the natural mechanisms of frankincense creation in the tree will point the way toward methods of producing it efficiently.