Gene switch underlying tomato fruit size and domestication

Gene switch underlying tomato fruit size and domestication

Tomato breeding has resulted in cultivars with increased fruit size relative to the wild ancestor Solanum pimpinellifolium. Mutations in the fasciated (fas) and locule number (lc) genes have been shown to underpin extreme fruit size in cultivated tomatoes—a feature largely determined by the number of seed compartments in mature fruits.

The researchers report that mutations in the gene switch excessive number of floral organs (eno) result in large-fruited varieties and may have played a crucial role in boosting fruit size during tomato domestication.

Compared with wild-type plants, eno mutants produced larger flowers as well as larger and heavier fruits, resulting in higher yield. Expressed in regions called shoot and flower meristematic domes, the gene switch belongs to a gene network repressing floral meristem activity; mutations disabling eno enable floral meristem enlargement.

Analysis of natural genetic variation in eno among more than 100 tomato accessions of varying fruit sizes revealed a link between the promoter sequence of the gene encoding eno and the number of seed compartments. Specifically, the absence of an 85-bp DNA fragment within the eno promoter was associated with increased number of seed compartments.

Analysis of the evolutionary history of this genomic region in the eno promoter in more than 600 tomato accessions revealed that deletion of the 85-bp region likely occurred before domestication and increased in frequency in cultivated tomatoes, setting the stage for larger fruits through breeding and selection of fas and lc mutants.

According to the authors, the study identifies a gene switch as a novel regulator of tomato fruit size that may have played a key role in domestication.