of pollen-dominant haplotype class is recessive to - of pollen-recessive haplotype class in .

encodes the male determinant of recognition specificity of self-incompatibility (SI) in species and is sporophytically expressed in the anther tapetum. Based on dominance relationships in pollen and nucleotide sequence similarity, the haplotypes in have been classified as class I or class II, with class-I haplotypes being dominant over class-II haplotypes. Here, we revealed that in belonging to class I is recessive to class-II and class-I in pollen, whereas it is dominant over , , and based on pollination tests. of () was sequenced, revealing that the deduced amino-acid sequence of SCR-22 has the longest C-terminal domain among the SCR/SP11 sequences. The expression of was found to be suppressed in and heterozygotes. Normal transcription of was considered to be due to the transcription suppression of sRNA of the haplotype and a very low methylation state of the promoter region in the tapetum of heterozygotes. In , only the cytosine residue located at the -37 bp position of the promoter region was hypermethylated in the tapetum of heterozygotes, and few methylated cytosines were detected in the promoter and coding regions of in heterozygotes. was also expressed in microspores in homozygotes but not in and heterozygotes. These results suggest that a mechanism different from class-II / suppression may operate for the suppression of recessive class-I in heterozygotes.