An international consortium of plant scientists has completed the first sequencing of the banana genome.
Bananas (Steve Hopson / www.stevehopson.com)
The banana genome was found to contain more than 36,000 genes, slightly more than the human genome. The results are published in the journal Nature.
“We are dealing with huge amounts of information,” said co-author Dr Eric Lyons, an assistant professor in the University of Arizona School of Plant Sciences. “Plant genomes are incredibly dynamic, which makes them some of the most fascinating and at the same time most difficult organisms to study.”
Of the many varieties of banana, whose scientific name is Musa acuminata, one called DH-Pahang is a breed known for its susceptibility for disease, making it a poor crop choice. Shunned by the agriculture industry, DH-Pahang rose to stardom when the sequencing team, led by two French research organizations, CIRAD and CEA-Genoscope, chose the variety for its project.
The DH-Pahang banana differs from its relatives in that it has what geneticists call a homozygous genome.
“It means both copies of each chromosome are identical,” Dr Lyons explained. “Working with a homozygous genome makes it easier to solve the jigsaw puzzle of the genome and correctly assemble all the pieces. You don’t get confused by having slightly different puzzle pieces, or sequences, for gene alleles across a genome.”
According to the consortium, bananas are vitally important for the food and economic security of more than 400 million people in southern countries, but they are under constant pressure from a range of parasites. That pressure is particularly high in plantations producing the ‘export’ bananas we find in our supermarkets. This makes it crucial to develop new, more resistant varieties, although this is a complex operation given the very low fertility of cultivated banana varieties.
The newly available genome sequence provides access to each one of the plant’s genes and to their position on its 11 chromosomes. The consortium said in a statement that this knowledge will make it much easier to identify the genes responsible for characters such as disease resistance and fruit quality. Lastly, it will be a vital tool for improving banana varieties using the many genetic resources available worldwide.
The banana is the first non-grassy plant in its botanical class, the monocotyledons, whose entire genome has been sequenced. Monocots include grasses, palms, lilies and other plants of mostly fleshy stature. Dicots, on the other hand, comprise more evolutionary recent plants including the majority of flowering plants and all true trees.
“The banana is the first monocot genome we have sequenced that’s not from a cereal,” Dr Lyons said. “That gives us a good opportunity to compare this group to its distant relatives and better understand the evolution of the monocot lineage.”
Already, researchers have been able to establish that banana has seen three episodes of complete genome duplication, at least two of which are independent of those seen in grasses. Unlike in the animal kingdom, duplicating an entire genome is nothing unusual in the plant world.
“We sometimes joke that you as soon as you give a plant a funny look, it doubles its entire genome,” Dr Lyons said.
This phenomenon, called polyploidy, is one of the main reasons why plant genomes present a challenge for scientists like Dr Lyons, who are interested in understanding how genomes have changed over evolutionary time and relate that to the function of the organism.
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Bibliographic information: D’Hont et al. 2012. The banana (Musa acuminata) genome and the evolution of monocotyledonous plants. Nature, published online 11 July 2012; doi: 10.1038/nature11241
