Gene tinkering for dream hybrids
doi:10.1038/nindia.2008.114 Published online 20 February 2008
Plant genetisists from Hyderabad have achieved a feat that plant breeders have been dreaming for decades. They have identified a gene in plants that can be engineered to create crops whose hybrid vigor and most agronomic traits remain intact from one generation to the next.
The team from Centre for Cellular and Molecular Biology (CCMB) — Maruthachalam Ravi, Mohan P. A. Marimuthu and Imran Siddiqi — has described the molecular mechanism of how seeds are formed asexually in plants — a phenomenon called apomixis.
Apomixis occurs naturally in about 400 plant species. It happens when the plant somehow manages to avoid the more prevalent phenomenon of meiosis — a special type of cell division that produces cells having one copy of the genetic material instead of two.
"Our results show that the alteration of a single gene in a sexual plant can bring about functional apomeiosis, a major component of apomixis," says Imran Siddiqi, one of the researchers. This finding provides a breakthrough for engineering apomixis, one of the most important future technologies for agriculture, particularly for developing countries with growing populations.
Apomictic seeds are genetically identical to the maternal plant. The transfer of apomixis to food crops where it does not naturally occur, would allow stable propagation of high yielding hybrid seeds by the phenomenon called selfing, over successive generations. This will be a departure from the current practice of synthesizing new seeds each time by crossing two different plants. Consequently, the reduced cost of hybrid seeds would contribute to large yield increases (20 per cent or more) across several major crops.
However, he cautions that to take the technology further, scientists need to identify genes that control apomixis and manipulate them in crops. Apomixis is thought to be controlled by more than one gene, but these remain to be identified at the molecular level.
Two major components of apomixis are apomeiosis — the formation of an unreduced (diploid) female gamete that is genetically identical to the parent plant, and parthenogenesis — the development of an embryo without fertilization of the egg cell.
The CCMB study shows that alteration of a gene called DYAD/SWI1, a known regulator of chromosome organization during meiosis, leads to formation of apomeiotic seeds.
"This is an exciting result because it shows for the first time that it is possible to bring about a major functional component of apomixis by altering a gene whose molecular identity is known, thereby showing how apomeiosis may be achieved in a wide range of plants," he says.
The finding brings scientists closer to synthesizing apomixis in crop plants, a major goal of agricultural biotechnology, Siddiqi says.
"This certainly is a breakthrough in plant genome research," says Asis Datta, director of the National Institute of Plant Genome Research in New Delhi. "Though we don’t yet know how early we will reap the benefits of the finding, it looks like a milestone in hybrid plant engineering," he adds.
- Ravi, M. et al. Gamete formation without meiosis in Arabidopsis. Nature doi: 10.1038/nature06557 (2008)