Isolation of three distinct CycD3 genes expressed during fruit development in tomato.

Tomato (Lycopersicon esculentum Mill.) is an important fruit crop world-wide and a model for studying fruit development. As determined using flow cytometry, fruit growth was characterized by high cell division activity in tomato during the first week after anthesis and followed by endoreduplications (DNA replication without cell divisions). D-type cyclins are considered to be important parts of the signal transduction for stimulation of DNA replication and cell division. To study the function of D cyclins in fruit development, full-length cDNA clones for three D cyclin genes were isolated from young tomato fruit. They were classified as D3 cyclins by sequence similarities and a phylogenetic analysis and named as LeCycD3;1, LeCycD3;2 and LeCycD3;3. The deduced amino acid sequences for LeCycD3;1-3 contained a retinoblastoma-binding motif and a PEST-destruction motif. Pollination and fertilization were followed by a high increase in the transcript levels of LeCycD3;1-3 in young fruit. Using in situ hybridization, high expression of LeCycD3;3 was detected in the vascular tissue of young fruit suggesting a role in vascular development. The D3 cyclins are probably involved in transducing the signals leading to fruit growth by cell divisions. Distinct differences were detected in their temporal and spatial expression patterns suggesting that they play different roles in fruit development as well as in the development of other plant organs.