SCR-22 of pollen-dominant S haplotype class is recessive to SCR-44 of pollen-recessive S haplotype class in Brassica rapa

Self-incompatibility: Rethinking hierarchy Studies in cabbage plants shed new light on self-incompatibility mechanisms to avoid self-fertilization. In Brassica, self-incompatibility is controlled by the expression of dominant and recessive genetic variants in the S-locus region. These variants encode proteins that mediate the rejection of self-pollen, but little is known about how the dominance relationship is established between them. Takeshi Nishio at Tohoku University in Japan and colleagues have examined the sequence, expression pattern and dominance relationships of the gene encoding the pollen-coat protein SCR-22. Despite sharing features with dominant SCR variants, SCR-22 can act in a recessive manner. Interestingly, unlike other recessive SCR variants, the suppression of SCR-22 expression does not depend on the addition of methyl groups that prevent transcription factor binding. This finding suggests the dominance hierarchy is governed by different mechanisms.