The genetic basis of seed-weight variation: tomato as a model system

The seeds of domesticated plants are normally much larger than those of the ir wild counterparts. This change in seed weight was most likely in respons e to the selection pressure for yield, uniform germination and seedling vig or which was exerted by humans during domestication. However, despite the e volutionary and agronomic significance of seed weight, very little is know about the genetic and developmental controls of this trait; and, thus far, none of the genes in this pathway have been isolated from any plant species . QTL mapping experiments conducted in tomato during the past decade have a llowed the identification of many seed-weight QTLs and have also revealed t hat only a few loci are responsible for the majority of the seed-weight cha nges that accompanied the domestication of tomato. This review presents a c onsensus map for seed weight QTL identified in previously published reports and in unpublished results from our laboratory. This summary of seed-weigh t QTL data allows for the identification of the major loci controlling this trait in the genus Lycopersicon. It is hoped that this work will allow the elucidation of this important phenotypic transition that occurred during c rop-plant domestication and will also provide the starting point for the cl oning of a gene responsible for seed-weight variation.