S locus glycoprotein (SLG) and S locus receptor kinase (SRK) cDNAs wer
e isolated from an S allele present in a number of self-compatible Bra
ssica napus lines. This A10 allele did not segregate with self-incompa
tibility in crosses involving other self-incompatible B. napus lines.
The SLG-A10 cDNA was found to contain an intact open reading frame and
was predicted to encode an SLG protein with sequence similarities to
those previously associated with phenotypically strong self-incompatib
ility reactions. SLG-A10 transcripts were detected in the developing s
tigma at steady state levels even higher than those detected for SLG a
lleles linked with self-incompatibility. Analysis of the corresponding
SRK-A10 cDNA showed that it was very similar to other S locus recepto
r kinase genes and was expressed predominantly in the stigma. However,
a 1-bp deletion was detected in the SRK gene toward the 3' end of the
SLG homology domain. This deletion would lead to premature terminatio
n of translation and the production of a truncated SRK protein. The A1
0 allele was determined to represent a B. oleracea S allele based on i
ts segregation pattern with the B. oleracea S24 allele when both these
alleles were present in the same B. napus background. These results s
uggest that a functional SRK gene is required for Brassica self-incomp
atibility.