doi:10.1038/nindia.2013.0 Published online 6 January 2013
Researchers at the National Institute of Plant Genome Research (NIPGR) in New Delhi claim to have achieved what every plant molecular biologist has been dreaming of: empowering a crop with multiple traits by genetic modification (GM) using a single gene.
In recent years, development of transgenic crops with multiple desirable traits such as drought tolerance, disease resistance and improved nutrient content has emerged as an important area in the field of plant biotechnology. Introduction of several traits in a crop requires manipulation of more than one gene. This can, in principle, be achieved by stacking more than one gene either by genetic engineering or conventional cross-breeding of plants already genetically modified for a single trait. "However this strategy is time consuming and labour intensive," says Asis Datta, Professor of Eminence at NIPGR.
Datta and co-workers now report1 successful creation of a transgenic tomato that is tolerant to drought, resistant to fungal infection and at the same time nutritionally rich with more iron and polyunsaturated fatty acids (PUFA) content. The multiple traits were imparted to the tomato by transferring a single gene to the tomato plant. They derived the gene from an edible fungus called Flammulina velutipes. This gene is said to code for the enzyme C-5 sterol desaturase (FvC5SD).
"To our knowledge, this is the only report showing that expression of a single gene can improve biotic/abiotic stresses as well as nutritional quality at the same time," Datta, who led the research told Nature India.
Enhanced drought tolerance is one of the important traits exhibited by transgenic tomatoes expressing FvC5SD, the report said. Normally, the presence of paraffin like wax called 'epicuticular wax' in the plant leaves protects plants from water loss and drought. The researchers said that wax deposition in their transgenic tomatoes was found to be 23 per cent more than in non-transgenic tomatoes. "The increased amount of wax deposition in transgenic tomato plants confer enhanced drought tolerance," Datta said.
The scientists tested the drought tolerance capability by stopping water supply to both transgenic and control (non-transgenic) plants. While all the wild type plants wilted away by the tenth day, the transgenic plants remained fresh for 17 days, the report said.
Epicuticular wax layer, according to the researchers, not only acts as a shield against drought but also against fungal disease by becoming the first barrier for invading pathogens from coming into direct contact with the underlying epidermal cells. "Therefore, increased epicuticular wax accumulation in transgenics expressing FvC5SD should lead to enhanced resistance to fungal attack," Datta explained. Since tomato is the natural host of the fungus Sclerotinia sclerotiorum, the scientists tested its ability to infect leaves of the wild type and transgenic plants. The transgenic plants "showed a slow progress of disease when compared to wild type plants," the report said.
FvC5SD is an iron-binding protein and its expression leads to enhanced total iron content in transgenic tomato, as the researchers found out by atomic absorption spectroscopy. According to their report, the transgenic tomatoes contained two to three times more iron than the control plants. This is particularly encouraging, says Datta, since, "iron deficiency is the most widespread micronutrient deficiency, affecting about two billion people."
Furthermore, the researchers claim that the transgenic tomatoes have improved nutritional value attributed to enhanced level of PUFA known to have diverse roles in metabolism, cardiovascular health, inflammatory responses and blood pressure regulation. According to the report the amount of PUFA in the transgenic tomatoes was found to be approximately 1.5 to 5 times more than in non- transgenic tomatoes.
While the genetic transformation in this work pertained to tomatoes,the strategy can be extended to other economically important crops, says Datta.