Plant improvement depends on recognizing and combining particular sets of genes. A multinational genome project to identify important plant genes, focusing on the model species Arabidopsis thaliana is nearing completion.

Thale cress (Arabidopsis thaliana) is the best characterised weed on earth. It is a small herbaceous annual of the Brassicaceae, and has been used in experimental research for nearly a century. At the end of last year, a group of 200 scientists from 35 laboratories around the world published the DNA sequence, or genetic code, for two of the tiny weed's five chromosomes. The other three are expected to be completely sequenced by the end of 2000.

It is the small size, quick growing time and small amount of DNA in Arabidopsis that make it so readily amenable to genetic analysis. The close resemblance of many Arabidopsis genes to genes in distantly related crops such as oilseed rape, wheat, and rice make the analysis even more exciting. Many individual genes in Arabidopsis have counterparts that carry out the same function in crop plants. Revealing the location and function of all Arabidopsis genes will help identify the genes controlling the same processes in more complex crop plants; an essential step towards more efficient and novel routes to plant improvement.

Determining the DNA sequence of Arabidopsis and the role of some of the genes is therefore, just the start. Ultimately, scientists hope to understand what each of the estimated 26,000 genes does, how the product of each gene acts and how all of this genetic activity works in concert to make a plant. Progressing from DNA sequence data to an understanding of the function of every gene in an organism is the biggest challenge in modern biology. In recent years a number of "high-throughput" techniques have been developed to help speed up the process and the collective application of these techniques has become known as "functional genomics".

In the past few years, several genes have been characterised. For example, two genes that act as switches for triggering flower formation at the ends of shoots have been discovered. Other researchers are exploring ways of using Arabidopsis genes to do the exact opposite - prevent flowering. The purpose here is not just to prevent "transgenes" spreading into wild relatives. For annual crops such as lettuce and potato plants, flowering is a prelude to death. It sends a signal to the leaves telling them to shut down photosynthesis. Blocking that signal might mean farmers could grow the crops for longer and perhaps get bigger yields because the plants would no longer need to invest resources in making flowers. Another Arabidopsis gene called "Frigida" could function as its name suggests--to prevent flowering, or at least to delay it until winter is over.

At present, the function of about a third of plant gene sequences is a guessing game, but by using the functional genomics developed for Arabidopsis, it should soon be possible to predict the role of most of the key genes in the major cereals.

FOOD TODAY 07/2000