A 7-kDa pollen coating-borne peptide from Brassica napus interacts with S-locus glycoprotein and S-locus-related glycoprotein

Two S(self-incompatibility)-family glycoproteins have been identified in stigmas of self-compatible (SC) Brassica napus L. by their ability to interact, in vitro, with a peptide fraction from the pollen coating containing a PCP⁷-like peptide, PCP⁷ (pollen coat peptide 7[kDa]) being a pollen coat peptide from self-incompatible (SI) Brassica oleracea L. which has been shown to interact with S-locus glycoproteins (SLGs). Electrophoretic purification and N-terminal amino-acid sequencing of these stigmatic glycoproteins confirmed one to be an SLG and the other to be a class 1 S-locus-related glycoprotein (SLR1). This is the first reported isolation of SLG and SLR1 proteins from SC B. napus and the first time that a PCP⁷-like peptide has been shown to interact with an S-class glycoprotein other than SLG. On the basis of these findings we suggest that an ability to interact with PCP⁷ or a PCP⁷-like peptide is a property of SLGs, SLR1s and possibly other S glycoproteins and may thus provide a novel route to the identification of these glycoproteins in stigmatic extracts. The levels of the SLG in stigmas of SC B. napus were relatively much lower than the levels of the SLR1-the opposite to the situation in SI B. oleracea. This finding is discussed in terms of translational control of SLGs and SLR1, and the possible implications for self-incompatibility in B. oleracea and self-compatibility in B. napus.