Functional characterization of the tomato cyclin-dependent kinase inhibitor SlKRP1 domains involved in protein-protein interactions

P>Cyclin-dependent kinase (CDK) inhibitors (kip-related proteins, KRPs) play a major role in the regulation of plant cell cycle in antagonizing its progression, and are thus regulators of development. The primary sequence of KRPs is characterized by the existence of conserved motifs, for which we have limited information on their functional significance. We performed a functional analysis of various domains present in KRPs from tomato. A series of deletion mutants of SlKRP1 was generated and used in transient expression assays to define the relevance of conserved protein domains in subcellular and subnuclear localizations. Specific interactions of SlKRP1 and its deletion variants with cell cycle proteins were investigated using two-hybrid assays and bimolecular fluorescent complementation. Plant KRPs are distributed into two phylogenetic subgroups according to the presence of conserved motifs. Members of subgroup 1 represented by SlKRP1 share 6 conserved motifs whose function in protein localization and protein-protein interactions could be identified. A new interaction motif was localized in the central part of SlKRP1 that targets SlCDKA1 and SlCYCD3;1 to the nucleus. Our results bring new insights to the functional role of particular domains in KRPs relative to subcellular localization or proteolytic degradation.