Developmental characterization of the fasciated locus and mapping of Arabidopsis candidate genes involved in the control of floral meristem size and carpel number in tomato.

Mutation at the fasciated locus was a key step in the production of extreme fruit size during tomato domestication. To shed light on the nature of these changes, near-isogenic lines were used for a comparative developmental study of fasciated and wild-type tomato plants. The fasciated gene directly affects floral meristem size and is expressed before the earliest stages of flower organogenesis. As a result, mature fruit of fasciated mutants have more carpels (locules) and greater fruit diameter and mass. The discovery that fasciated affects floral meristem size led to a search for candidate genes from Arabidopsis known to be involved in floral meristem development. Putative homologs were identified in a large tomato EST database, verified through phylogenetic analyses, and mapped in tomato; none mapped to the fasciated locus; however, putative homologs of WUS and WIG mapped to the locule number locus on chromosome 2, the second major transition to large tomato fruit, with WUS showing the highest association. In other cases, minor QTLs for floral organ number (lcn2.2) and (stn11.2) co-localized with a CLV1 paralog and with the syntenic region containing the CLV3 gene in Arabidopsis, respectively.