MLPK function is not required for self-incompatibility in the S29 haplotype of Brassica rapa L.

Abstract

Key message S 29 haplotype does not require the MLPK function for self-incompatibility in Brassica rapa . Abstract Self-incompatibility (SI) in Brassicaceae is regulated by the self-recognition mechanism, which is based on the S -haplotype-specific direct interaction of the pollen-derived ligand, SP11/SCR, and the stigma-side receptor, SRK. M locus protein kinase (MLPK) is known to be one of the positive effectors of the SI response. MLPK directly interacts with SRK, and is phosphorylated by SRK in Brassica rapa . In Brassicaceae, MLPK was demonstrated to be essential for SI in B. rapa and Brassica napus , whereas it is not essential for SI in Arabidopsis thaliana (with introduced SRK and SP11/SCR from related SI species). Little is known about what determines the need for MLPK in SI of Brassicaceae. In this study, we investigated the relationship between S -haplotype diversity and MLPK function by analyzing the SI phenotypes of different S haplotypes in a mlpk / mlpk mutant background. The results have clarified that in B. rapa , all the S haplotypes except the S 29 we tested need the MLPK function, but the S 29 haplotype does not require MLPK for the SI . Comparative analysis of MLPK-dependent and MLPK-independent S haplotype might provide new insight into the evolution of S -haplotype diversity and the molecular mechanism of SI in Brassicaceae.

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