A New C-Type Cyclin-Dependent Kinase from Tomato Expressed in Dividing Tissues Does Not Interact with Mitotic and G1 Cyclins

Cyclin-dependent kinases (CDKs) form a conserved superfamily of eukaryotic serine-threonine protein kinases whose activity requires the binding of a cyclin protein. CDKs are involved in many aspects of cell biology and notably in the regulation of the cell cycle. Three cDNAs encoding a C-type CDK, and a member of each B-type CDK subfamily, were isolated from tomato (Lycopsersicon esculentum Mill.) and designated Lyces;CDKC;1 (accession no. AJ294903), Lyces; CDKB1;1 (accession no. AJ297916), and Lyces;CDKB2;1 (accession no. AJ297917). The predicted amino acid sequences displayed the characteristic PITAIRE (CDKC), PPTALRE (CDKB1), and PPTTLRE (CDKB2) motives in the cyclin-binding domain, clearly identifying the type of CDK. The accumulation of all transcripts was associated preferentially with dividing tissues in developing tomato fruit and vegetative organs. In contrast to that of CDKA and CDKBs, the transcription pattern of Lyces;CDKC;1 was shown to be independent of hormone and sugar supply in tomato cell suspension cultures and excised roots. This observation, together with the absence of a patchy expression profile in in situ hybridization experiments, suggests a non-cell cycle regulation of Lyces;CDKC;1. Using a two-hybrid assay, we showed that Lyces;CDKC;1 did not interact with mitotic and G1 cyclins. The role of plant CDKCs in the regulation of cell division and differentiation is discussed with regard to the known function of their animal counterparts.