Phosphorylation of pollen proteins in relation to self-incompatibility in rye (Secale cereale L.)

Abstract

The gametophytic two-locus self-incompatibility (SI) system in rye was investigated in view of a possible involvement of protein phosphorylation and Ca2+ as constituents of a signal transduction mechanism. Phosphorylation kinetics in pollen grains was found to be significantly different after in vitro treatment of pollen with either “cross” or “self” stigma proteins, with a pronounced phosphorylation activity in self-treated pollen grains. Loss of SI in self-compatible (SC) mutants was associated with a significantly decreased basic phosphorylation activity in untreated pollen grains as compared to SI genotypes. Separation of phosphorylated pollen proteins by SDS-PAGE reveals four major proteins in the MW range of 43–82 kDa which were differently phosphorylated in SI vs SC genotypes as well as in cross vs self-treated pollen grains. Application of different protein kinase inhibitors and the Ca2+ antagonists verapamil and La3+ to isolated stigmas resulted in an inhibition of the SI response in in vitro self-pollination. The role of protein kinases and Ca2+ as constituents of a putative SI-specific signal transduction mechanism is discussed.