Identification, Expression and Functional Analysis of a Receptor-like Cytoplasmic Kinase, OsRLCK1, in Rice

Pollination involves a series of complex cellular interactions and signal transduction events. Numerous reports have suggested a central role for protein kinases in pollen germination and pollen tube growth and a large number of receptor-like kinases have been detected exclusively in pollen in higher plants. However, few are well characterized, especially for the receptor-like cytoplasmic kinases. Here we report a receptor-like kinase gene, OsRLCKI, which belongs to the receptor-like cytoplasmic kinase VIM subfamily. Real-time quantitative polymerase chain reaction analysis and whole mount RNA in situ hybridization showed that OsRLCKI is a pollen-specific gene and expressed only in the mature pollen. When expressed in the onion epidermal cells, the OsRLCK1-GFP fusion protein was diffused throughout the cell, indicating its cytoplasmic and nuclear localization. The Maltose Binding Protein-OsRLCKI recombinant protein was found to be capable of autophosphorylation on threonine residue, showing that it encodes a functional kinase. These results suggest that OsRLCKI is likely to play a role in a signaling pathway associated with pollen performance during pollination in rice.