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 c yclin protein. CDKs are involved in many aspects of cell biology and notabl y in the regulation of the cell cycle. Three DNAs encoding a C-type CDK, an d a member of each B-type CDK subfamily, were isolated from tomato (Lycopse rsicon esculentum Mill.) and designated Lyces; CDKC;1 (accession no. AJ2949 03.), Lyces; CDKB1;1 (accession no. AJ297916), and Lyces;CDKB2;1 (accession no, AJ297917). The predicted amino acid sequences displayed the characteri stic PITAIRE (CDKC), PPTALRE (CDKB1), and PPTTLRE (CDKB2) motives in the cy clin-binding domain, clearly identifying the type of CDK. The accumulation of all transcripts was associated preferentially with dividing tissues in d eveloping tomato fruit and vegetative organs. In contrast to that of CDKA a nd CDKBs, the transcription pattern of Lyces;CDKC;1 was shown to be indepen dent of hormone and sugar supply in tomato cell suspension cultures and exc ised roots. This observation, together with the absence of a patchy express ion profile in in situ hybridization experiments, suggests a non-cell cycle regulation of Lyces;CDKC;I. Using a two-hybrid assay, we showed that Lyces ;CDKC;1 did not interact with mitotic and G1 cyclins. The role of plant CDK Cs in the regulation of cell division and differentiation is discussed with regard to the known function of their animal counterparts.