AN S5 SELF-INCOMPATIBILITY ALLELE-SPECIFIC CDNA SEQUENCE FROM BRASSICA-OLERACEA SHOWS HIGH HOMOLOGY TO THE SLR2 GENE

The sequence is reported of a cDNA molecule homologous to an mRNA from stigma tissue of Brassica oleracea plants homozygous for the S5 self- incompatibility allele. This cDNA is closely related to a previously p ublished sequence designated SLR2, which was obtained from the same st igma cDNA library and is also related to the SLR1 gene, a cDNA for whi ch has also been obtained from this library. Various B. oleracea lines differing in S alleles and of different varieties have been screened for the presence of particular S gene family sequences using a method involving hybridization of sequence-specific oligonucleotide probes to PCR products. The results indicate that a gene homologous to the sequ ence presented here is absent from a line lacking the S5 allele, thoug h present in other lines containing the S5 allele, regardless of their genetic background. This finding suggests that the sequence represent s a transcript of the SLG (S locus glycoprotein) gene. A similar appro ach has confirmed that a cDNA derived from a Brassica line containing the S29 allele is also S allele-specific. The predicted amino acid seq uences derived from a number of S gene family sequences are compared u sing numerical methods and possible evolutionary relationships between them are discussed.