Expression of CycD3 is transiently increased by pollination and N-(2-chloro-4-pyridyl)-N'-phenylurea in ovaries of Lagenaria leucantha.

Lagenaria leucantha is an important vegetable crop and a potential model for the study of fruit development. To study the function of D cyclins in fruit development, full-length cDNA clones for two D cyclin genes were isolated from young ovaries of Lagenaria leucantha. They were classified as D3 cyclins by sequence similarities and phylogenetic analysis, and nominated LlCycD3;1 and LlCycD3;2, respectively. The deduced amino acid sequence of both LlCycD3 genes contained a retinoblastoma-binding motif and a PEST-destruction motif. Unpollinated ovaries failed to develop and eventually aborted. N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) induced parthenocarpic fruit significantly larger than pollinated ones. In unpollinated ovaries, the expression of both LlCycD3 genes was abundant at anthesis and then suddenly decreased, concomitant with the cessation of cell division. Pollination/fertilization induced an activation of the cell cycle accompanied by a large increase in the transcript levels of LlCycD3;1 and LlCycD3;2 in young fruits. Treating ovaries with CPPU also reactivated cell division and transcription of CycD3 genes and the effect was more rapid and pronounced than after pollination/fertilization.