Bar-coding plants

It may soon be possible to classify a majority of the more than 400,000 species of land plants in the world on the basis of genetic variability. The Plant Working Group of the Consortium for the Barcode of Life (CBOL) recently reached a consensus on the portions of the genes that would be used as the plant DNA bar-code. This came after four years of work by 52 scientists from 10 countries. DNA bar-coding, a technique proposed by the University of Guelph, Ontario, Canada, uses a short genetic sequence from a standard part of the genome to quickly identify different plant species. To become usable the chosen genetic sequences of the bar-code must vary with species but must also be conserved enough in plants for identifying most of them. Bar-coding has been used since 2003 to identify animal species, and a bar-code library of nearly 60,000 animal species has been created. But there was no agreement on which regions of the genome should be used for bar-coding plants. The short DNA sequence found in the mitochondrial gene used for bar-coding animals cannot be used in plants; this is because the gene does not vary much in plants and will not be reliable for species identification. Attention therefore turned on the chloroplast genome, which converts sunlight into chemicals. Of the seven candidates shortlisted, the Plant Working Group chose portions of two genes ( matK and rbcL) for the bar-code. But the plant bar-code is some way short of the ideal. While it can group the plants to the correct genus, it can, on average, discriminate only 72 per cent of all plant species. Though identifying closely related species is problematic in many plants and fungi, it should be less of an issue when used within a restricted region or habitat. But there is no room for complacency as this tool is yet to be tested widely in biodiversity hotspots. The gene used in the animal bar-code has the power to correctly identify over 95 per cent of the species. The task then is to find a way to increase the discriminatory power of the plant bar-code. In the short-term, using supplementary bar-codes along with the standard one can increase this power. But the biggest challenge the initiative may have to face will be funding. Most biodiversity hotspots are in developing countries that will not be able to fund such initiatives on their own. The irony is that some projects in India are yet to get off the ground for want of funding even as several agencies wait for a bar-code system to be settled to fund such initiatives. The time for determined action in this scientifically important area is now.
The Hindu, 17th August 2009