Regulation of early tomato fruit development by the diageotropica gene.

The vegetative phenotype of the auxin-resistant diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) includes reduced gravitropic response, shortened internodes, lack of lateral roots, and retarded vascular development. Here, we report that early fruit development is also dramatically altered by the single-gene dgt lesion. Fruit weight, fruit set, and numbers of locules and seeds are reduced in dgt. In addition, time to flowering and time from anthesis to the onset of fruit ripening are increased by the dgt lesion, whereas ripening is normal. The dgt mutation appears to affect only the early stages of fruit development, irrespective of allele or genetic background. Expression of members of the LeACS (1-aminocyclopropane-1-carboxylic acid synthase, a key regulatory enzyme of ethylene biosynthesis) and LeIAA (Aux/IAA, auxin-responsive) gene families were quantified via real-time reverse transcriptase-polymerase chain reaction in both dgt and wild-type fruits, providing the first analysis of Aux/IAA gene expression in fruit. The dgt lesion affects the expression of only certain members of both the LeACS and LeIAA multigene families. Different subsets of LeIAA gene family members are affected by the dgt mutation in fruits and hypocotyls, indicating that the DGT gene product functions in a developmentally specific manner. The differential expression of subsets of LeIAA and LeACS gene family members as well as the alterations in dgt fruit morphology and growth suggest that the early stages of fruit development in tomato are regulated, at least in part, by auxin- and ethylene-mediated gene expression.