‘Clonal seeds are not too far into the future’

In nature,most plants reproduce sexually,producing progeny that inherit genetic traits from both parents. While this may be a key mechanism of evolution,with hybrid seeds it could mean that the second generation crop retains only some of the valuable traits genetically engineered into the parent. There has,therefore,been a concerted effort to produce ‘clonal seeds’ that retain all the genetic traits of the maternal parent,without any of the shuffling of genetic information that normally occurs with every generation. Imran Siddiqi,who received the Infosys Science Prize in the life sciences category last week,is one of several scientists looking to unravel the mysteries of asexual reproduction in plants. “There are two steps involved in creating clonal seeds—avoiding meiosis or sexual reproduction and inducing parthenogenesis or asexual reproduction. We know how to do the former,but the latter is still not very well understood,” says Siddiqi,who heads the plant genetics group at the Centre for Cellular and Molecular Biology in Hyderabad.

Siddiqi’s research group has demonstrated a proof of concept of apomixis in Arabidopsis thaliana,a weed related to mustard. By tweaking a gene that regulates meiotic chromosome organisation in the plant,the group could engineer apomeiosis: the formation of ‘unreduced’ female gametes that retain the genotype of the parent plant. Up to 34 per cent of the progeny thus produced were clones of their parent,and,significantly,they could be cloned again. The paper was published in the journal Science last year. “This is something like what the Wright Brothers did when they demonstrated human flight is possible—a lot of research followed before anyone could build airplanes. In another five years,I expect we will have a much better understanding of parthenogenesis. Clonal seeds for agriculture won’t be far behind then,” Siddiqi says.

“This could revolutionise agriculture for poor farmers. Take wheat,for instance. Today,the farmer has to buy hybrid seeds year after year. With apomictic breeding,genetic traits could be propagated indefinitely and seeds from one harvest could be used to produce the next,” says Inder Varma,a distinguished molecular biologist and professor at the Salk Institute for Biological Studies,US,who chaired the Infosys Science Prize jury for life sciences.

Apomixis,which is thought to have evolved from sexuality,occurs naturally in about 400 species of plants,among them hawkweed,an asexually reproducing plant that stumped Gregor Mendel,the father of modern genetics who showed that the inheritance of genetic traits follows a certain pattern. Scientists have,however,been largely unsuccessful in their attempts to cross apomictic wild varieties with sexual crop varieties. “The answer lies in understanding the molecular mechanisms underlying apomixis,” says Siddiqi. “Only about 30 per cent of the seeds we were able to produce asexually were clonal. This success rate has to increase to 80 or 90 per cent,with negligible abortions or sexual seed formation,for the technology to be marketable.”