The Asexual Drive
Introduction
Scientists make a sexually reproducing plant go asexual
Asexual reproduction does have certain advantages over sexual reproduction when it comes to plants. It is faster, easier and requires less energy. Production is higher too. Seeds produced asexually are clones of the mother plant and have exactly the same traits. This takes away the need for constant cross-breeding needed to retain the desired traits. But asexual reproduction is rare in plants, and attempts at inducing it in crop plants have been unsuccessful till date.
Isabelle d'Erfurth at the French National Institute for Agricultural Research in Versailles in France and colleagues modified Arabidopsis thaliana, a flowering plant that reproduces sexually, to produce asexual seeds. A member of the mustard family, A thaliana has a well documented genome.
So it was easy for the team to stop meiosis—cell division that produces the egg and sperm cells. This made the team hopeful of transferring the technique to crop plants like wheat and corn.
Egg and sperm cells have half the chromosome number (haploid) of the vegetative cells (diploid), thanks to meiosis. The difference between asexually and sexually produced plants lies in three steps that define meiosis. Block these steps and the plant will still look the same, replete with egg and sperm cells. The only difference will be in the chromosome number. In an asexually produced plant even the egg and sperm cells will be diploid.
In 2005, the researchers blocked the first two steps in meiosis in a plant, which turned out to be infertile. This time they found a gene which helped them block the last step. The resultant plant was fertile. When two such genetically identical plants were crossed, it was equivalent to asexual reproduction, said the study, published in the June 9 issue of PloS Biology. But the chromosome number kept doubling as further generations were crossed.
Akshay Talukdar, division of genetics, Indian Agricultural Research Institute, Delhi, said, "Since the chromosome number in Arabidopsis is doubling with every generation, the plant may not be fertile after a certain point." Indeed the French team found that after three generations, when its chromosome number became eight, the plant produced hardly any seeds.
Source
Down To Earth, August 2009
