Two anther-expressed genes downstream of SLG ⁹: identification of a novel S-linked gene specifically expressed in anthers at the uninucleate stage of Brassica campestris (syn. rapa) L.

Abstract 

The sporophytic self-incompatibility (SI) system in Brassica campestris (syn. rapa) is controlled by multiple alleles of a single locus, S, in which SLG and SRK are located. SLG and/or SRK appear to comprise the female component of the recognition reaction of SI. The gene encoding the male component must also be located at the S locus but has not been identified to date. RNA gel blot analysis with regions flanking SLG ⁹ and SRK ⁹ revealed two anther-expressed genes 3’ of the SLG ⁹ gene. Two cDNA clones were isolated using the 3’-flanking region of SLG ⁹ as probe. Because of sequence similarity with the Brassica SLL2 gene, one cDNA clone was designated SLL2-S ⁹ (for S Locus-Linked 2-S ⁹ gene). The 5’-region of SLL2-S ⁹ was not present in other SLL2 genes examined. The second gene was novel and was designated SAE1-S ⁹ (for S locus Anther Expressed 1-S ⁹ gene). SAE1-S ⁹ and SLL2-S ⁹ were located approximately 2.5 kb and 5.5 kb, respectively, downstream of SLG ⁹. A 1.4-kb transcript for SLL2-S ⁹ was detected in both vegetative and reproductive tissues, whereas 1.9-kb and 2.4-kb transcripts were specifically detected in the anther of S ⁹ haplotype. SAE1-S ⁹ was specifically expressed in the anther at the uninucleate stage. This gene encoded a novel polypeptide of 257 amino acids. Database analysis revealed a homologous sequence in the upstream region of SRK ³ of B. oleracea. We discuss possible relationships between SLL2-S ⁹ and SAE1-S ⁹ and SI.