title: Gene expression and genetic analysis reveal diverse causes of recessive self-compatibility in Brassica napus L.
abstract: BACKGROUND
  Brassica napus (AACC) is self-compatible, although its ancestor species Brassica rapa (AA) and Brassica oleracea (CC) are self-incompatible. Most B.napus accessions have dominant self-compatibility (SC) resulting from an insertion of 3.6 kb in the promoter region of BnSCR-1 on the A genome, while recessive SC in B.napus has rarely been observed. Expression and cloning of SRK and SCR genes and genetic analysis were carried out to dissect bases of recessive SC in B.napus.
  
  
  RESULTS
  Eleven accessions were screened to identify stable recessive SC and had the S genotype BnS-7 on the A genome and BnS-6 on the C genome similarly to BrS-29 and BoS-15, respectively. In eight SC accessions, BnSCR-7 and BnSCR-6 were nearly undetectable and harbored no structural mutations in the promoters, while SRK genes were expressed at normal levels and contained intact CDS, with the exception of BnSRK-7 in line C32. SRK and SCR genes were expressed normally but their CDSs had no mutations in three SC accessions. In self-incompatible S-1300 and 11 F1 hybrids, SRK genes and BnSCR-1300 transcripts were present at high levels, while expression of the BnSCR-7 and BnSCR-6 were absent. Plants of S genotype S1300S1300 were completely SI, while SI phenotypes of SBnS-7SBnS-7 and S1300SBnS-7 plants were segregated in BC1 and F2 populations.
  
  
  CONCLUSIONS
  The recessive SC in eight accessions is caused by the loss of function of BnSCR-7 and BnSCR-6 in pollen. Translational repression contributes to the recessive SC in three accessions, whose SRK and SCR genes were expressed normally and had identical CDSs to BrS-29 or BoS-15. SI in 11 F1 hybrids relies on the expression of BnSCR-1300 rather than SRK genes. Other factor(s) independent of the S locus are involved in recessive SC. Therefore, diverse causes underlie recessive SC in B. napus, yielding insight into these complex mechanisms.
authors.forename: Wen
authors.initials: W
authors.lastname: Zhai
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Zhang
authors.forename: Yong
authors.initials: Y
authors.lastname: Yang
authors.affiliation: National Key Laboratory of Crop Genetic Improvement, National Center of Rapeseed Improvement in Wuhan, Huazhong Agricultural University, Wuhan 430070, People's Republic of China. yuanbeauty@mail.hzau.edu.cn.
authors.forename: Chaozhi
authors.initials: C
authors.lastname: Ma
authors.forename: Zhiquan
authors.initials: Z
authors.lastname: Liu
authors.forename: Changbin
authors.initials: C
authors.lastname: Gao
authors.forename: Guilong
authors.initials: G
authors.lastname: Zhou
authors.forename: Jinxing
authors.initials: J
authors.lastname: Tu
authors.forename: Jinxiong
authors.initials: J
authors.lastname: Shen
authors.forename: Tingdong
authors.initials: T
authors.lastname: Fu
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D029688:Brassica napus / Q000235:genetics*; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D006239:Haplotypes; D016254:Mutagenesis, Insertional; D010641:Phenotype; D011058:Pollen / Q000235:genetics*; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D012098:Reproduction / Q000235:genetics