A GENETICALLY DEFINED TRANS-ACTING LOCUS REGULATES S-LOCUS FUNCTION IN BRASSICA

A new locus, SCF1, which regulates S-locus function has been identified in Brassica campestris. The spontaneous scf1 mutation described in this paper causes the stigma to be receptive to all pollen including self-pollen, but does not affect the pollination phenotype of the male gametophyte. In the stigmas of scf1 homozygotes, the S-locus-linked SLG gene and two other unlinked members of the S-multigene family, all of which encode secreted glycoproteins, are coordinately down-regulated at the RNA level, while the expression of the S-locus-derived SRK gene, which encodes a putative receptor protein kinase, is unaffected. It is proposed that the SCF1 locus encodes a positive trans-acting factor required for the enhanced transcription of several genes in the stigmatic papillar cells during pistil maturation. The effects of the scf1 mutation provide strong support for the involvement of the cloned S-genes in the operation of the pollen-stigma interaction of incompatibility in B. campestris and related crucifer species.