Abstract
In Brassica self-incompatibility (SI), self/non-self recognition is controlled by S-haplotype-specific interaction between the pollen-borne ligand, SP11, and its stigmatic receptor-kinase, SRK. Our genetic analysis of a self-compatible mutant revealed the involvement of a cytoplasmic protein kinase, MLPK, in the SI signaling, but its exact physiological function remains unknown.
In this study, we identified two MLPK isoforms, named MLPKf1 and MLPKf2, localizing to the plasma membrane by different molecular mechanisms. While MLPKf1 and MLPKf2 exhibited distinct expression profiles, both were expressed in papilla cells. Although both MLPKf1 and MLPKf2 could independently complement the mlpk/mlpk mutation, their mutant forms that lack the plasma membrane localization motifs failed to complement the mutation. Furthermore, we showed direct interactions between SRK and MLPK in tobacco protoplasts. These results suggest that these MLPK isoforms interact directly with SRK on the plasma membrane to transduce SI signaling
