Genetic Basis of the Self-Incompatibility of a Brassica napus Line having been used for Hybrid Seed Production

Self-incompatibility (SI) is one of the most important strategies developed by flowering plants to prevent inbreeding and promote out-crossing.  In Brassica, the oilseed crop B. napus (AACC=38) is self-compatible though its two ancestor species B. oleracea (CC=18) and B. rapa (AA=20) are self-incompatible, where SI is controlled by a multi-allelic locus designated as S locus comprising of two highly polymorphic genes SRK (S-locus receptor kinase gene) and SP11/SCR (S-locus protein 11/S-locus cysteine-rich protein gene), determining the recognition specificity in the stigma and in the pollen, respectively. ‘S-1300’ is a self-incompatible Brassica napus line generated by introgressing an S haplotype from B. rapa ‘Xishuibai’ into a Brassica napus line ‘Huayou No. 1’. Hybrids from ‘S-1300’ as mother line have been delivered in China. ‘S-1300’ was detected to have two class II S haplotypes BnS-1300 and BnS-6 located on A and C genome, similar to BrS-47 and to BoS-15, respectively. BnSP11-1300 and BnSRK-1300 were cloned by homology-based candidate gene, sharing 100% identity of coding sequence with those of BrS-60.  Gene analysis and gene expression showed that BnS-1300 determines the SI in ‘S-1300’. S locus genes of B. napus lines ‘8400’ with dominant self-compatibility (SC) and ‘8403’ with recessive SC containing an S haplotype similar to Br47 and an S haplotype similar to Br29, respectively, were cloned.  Molecular markers were developed based on the sequences of S locus genes to distinguish S haplotypes among ‘S-1300’ and self-compatible lines. The self-incompatible line ‘S-1300’ having two recessive S haplotypes, an inter-specific pair maintaining the same recognition specificity, and the molecular markers based on S haplotype genes are usefulness both for detecting interactions of S haplotypes on intra- and inter- genomes and for breeding hybrids in B. napus.