Identifying gene function using rice mutants

The rice genome contains about 30,000 genes, half of which have an as yet undetermined role. The function of these genes can be found by analysing of a large population of plants in which a mutagen has been randomly inserted into each gene. Mutagens are short DNA sequences of different types that are used as tools to map and isolate genes ("molecular labels" so to speak). In the framework of the national plant genomics initiative Génoplante (see page 16), a team of researchers from Cirad-INRA-IRD-CNRS / University of Perpignan based at Montpellier has created a collection of rice insertion mutants large enough (100,000) so that each gene has a good probability of being interrupted at least once by an insertional mutagen, here the T-DNA from Agrobacterium tumefaciens. The collection of mutants will be progressively screened under various constraints in a controlled environment (confinement greenhouse, phytotrons) so as to identify plants of altered morphology, physiology or tolerance of environmental constraints, and subsequently to isolate the affected genes that govern the characteristics in question (forward genetics). The genome sequences adjacent to the T-DNA insertion sites in each mutant will be entered in a database. They will then be used to study the function of any gene with a known sequence, by searching for and then evaluating the relevant mutant carrying the altered sequence (reverse genetics). This will enable isolation of the rice genes involved in plant morphogenesis (architecture, flowering, embryogenesis and in the tolerance of biotic stress (diseases and pests) and abiotic stress (drought, salinity, mineral deficiency or toxicity). Molecular mapping of these genes will shed light on the genetic control of quantitative traits and will greatly facilitate varietal improvement in rice and other cereals (wheat, barley, maize, sorghum...). (Texte intégral