Student - October 23, 2008

Wageningen unravels first potato chromosome

Wageningen UR plant researchers proudly presented the DNA structure of Chromosome 5 of the potato on 16 October. It is the first potato chromosome that has been elucidated. The genes on Chromosome 5 control the time at which the potatoes can be harvested.

An international consortium with researchers from thirteen countries has been working to map the entire potato genome with its twelve chromosomes for two years. Wageningen is in charge of the consortium and was the first to have all the base pairs of one of the twelve chromosomes.

‘We first calculated the length of Chromosome 5’, says professor of Plant Breeding Richard Visser. ‘It concerns sixty million base pairs. We determined the site and sequence for 75 million base pairs, so there was some overlap. A few gaps are left here and there; some parts of the chromosome were difficult to map.’

Visser’s group can now start determining how many genes there are on chromosome 5 and where exactly they are. ‘We know that Chromosome 5 harbours interesting traits. In the follow-up research, we will link these traits with genes. That will lead to a template; we will then know for a specific base sequence of Chromosome 5 which desired trait it codes for. With the aid of that, we will be able to search for the gene for that characteristic much quicker in potatoes that perform much better.’

Meanwhile, Visser knows that genes on Chromosome 5 determine the so-called ‘earliness’ of the potato – you can harvest early species in July, but late species are not ready until November. ‘Early potatoes have low yields at the moment. We want to see if with the aid of this genetic information, we can develop an early variety with a high yield.’

The wait is now for the other participants –from the United States, China, India, Poland, Russia, New Zealand and Latin America – to have mapped their chromosomes. In Wageningen too, work is still ongoing to unravel the base sequence of a second chromosome. Then the consortium’s objective, the complete genome of 850 million base pairs in a row, will have been reached.

The Wageningen UR plant improvers Bjorn Kloosterman and Christiaan Bachem will now start looking for the genes that control the potato’s tuber formation and growth. To that end, they have placed all 44 thousand sequences of the potato genome on a chip called POCI, together with international colleagues. ‘The chip helps us zoom in more rapidly on a small group of genes’, says Visser. ‘We have already found a number of candidate genes, but we first have to prove that these genes are indeed important for tuber formation and growth.’