Naturally occurring variation in Arabidopsis: an underexploited resource for plant genetics

The definition of gene functions requires the phenotypic characterization o f genetic variants. Currently, such functional analysis of Arabidopsis gene s is based largely on laboratory-induced mutants that are selected in forwa rd and reverse genetic studies. An alternative complementary source of gene tic Variation is available: the naturally occurring variation among accessi ons. The multigenic nature of most of this variation has limited its applic ation until now. However, the use of genetic methods developed to map quant itative trait loci, in combination with the characteristics and resources a vailable for molecular biology in Arabidopsis, allow this variation to be e xploited up to the molecular level. Here, we describe the current tools ava ilable for the forward genetic analysis of this variation, and review the r ecent progress in the detection and mapping of loci and the cloning of larg e-effect genes.