International research team cracks sugarcane genome

After several years of arduous effort, scientists have mapped the genome of the sugarcane — a crop that produces 80 per cent of the world’s sugar and emerged as the primary crop for biofuel production. Because of its complex genetic makeup, it was one of the last crop plants to expose themselves to the tools of science.

A global team of researchers led by Angélique D’Hont of France’s CIRAD mapped the sugarcane genome using a variety grown in the Réunion Islands.

The findings, reported in the journal Nature Communications last week, will help scientists create a reference genome of sugarcane, which can be used to develop molecular tools to supplement conventional breeding methods. This reference sequence is also an essential resource to analyse the variations between the sugarcane varieties.

Until now, sugarcane cultivar breeding programmes were restricted to hybridisation, followed by cumbersome field assessments. As with all cultivated plants before it, sugarcane breeding will now be able to enter the age of molecular biology.

The genome is so complex that classical sequencing approaches proved useless, said Olivier Garsmeur, a CIRAD researcher and lead author of the study.

“The sugarcane genome is nearly 20 times bigger than that of rice. While the rice genome could be sequenced about 15 years ago, the sugarcane genome proved a tough nut to crack,” said G Hemaprabha, head-in-charge for crop improvement at ICAR’s Sugarcane Breeding Institute in Coimbatore.

Each of the 10 basic sugarcane chromosomes is duplicated in 8-10 copies with a total of more than 100 chromosomes. In comparison, the human genome has just 23 pairs of chromosomes, said Garsmeur.

The researchers, however, used yet another trick. Helping them was a discovery made at CIRAD some 20 years ago: the genomic structures of sugarcane and sorghum are very similar. The scientists were thus able to use the sorghum genome as a template to assemble and select the sugarcane chromosome fragments to sequence.

“We have identified around 25,000 sugarcane genes,”Garsmeur told BusinessLine.

According to Hemaprabha, the newly acquired genomic information will help sugarcane breeders develop varieties as per their requirements. For example, they can breed varieties that can withstand droughts, those requiring lesser water or cultivars containing higher sucrose levels.

“Theoretically, the maximum sucrose content that sugarcane can have is around 25 per cent. This, in principle, could be breached if we know the molecular mechanisms involved in sucrose storage in the plant,” she said.

While many major institutes working on sugarcane research in Australia, South Africa and elsewhere were involved in the research, India was not part of it. However, a private institute in Maharashtra — Vasantdada Sugar Institute — was part of a larger consortium sewn together by CIRAD. According to a scientist, India did not join the consortium because it had to make a hefty financial contribution.

However, Garsmeur said all countries can “use the data produced in our study even if they are not part of the consortium.”

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