Parthenocarpy and functional sterility in tomato

Parthenocarpy is the development of the fruit in absence of pollination and/or fertilization. In tomato (Solanum lycopersicum), parthenocarpy is considered as an interesting trait because it can improve fruit setting under environmental conditions that affect the viability of the pollen. Auxins and gibberellins are considered as the key players in parthenocarpic fruit development. An increased level of these hormones in the ovary can be a substitute for pollination and trigger fruit development. We characterized and mapped two sets of two parthenocarpy genes in two distinct tomato introgression lines carrying genome fragments of Solanum habrochaites (a related wild species of tomato). Tomato lines carrying these genes will produce seedless fruits in absence of pollination, and seeded fruits if the ovary is pollinated, thus affecting the uniformity of the production. The use of functional sterility in combination with parthenocarpy can overcome this problem of uniformity of seedless fruits production, but still allows seed production by hand pollination. The best functional sterility gene in tomato is likely to be the positional sterility-2 (ps-2) gene, which confers non-dehiscent anthers, containing viable pollen. We accurately determined the position of the ps-2 gene on the short arm of Chromosome 4. Subsequently, after the successful construction of a physical map in the ps-2 locus region, we isolated the ps-2 gene. The ps-2 phenotype appeared to be the result of a single nucleotide substitution in a novel tomato polygalacturonase gene, named TDPG (Tomato Dehiscence PolyGalacturonase). This single mutation affects one of the intron splicing recognition site, causing an alternative splicing of the mRNA, thus leading to an aberrant mRNA. The expression of this gene is specific to the dehiscent anthers and to a lesser degree to the mature fruit. The repression of TDPG homologs may be a potential way to introduce functional sterility in other species.