Abstract
BackgroundBrassica 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.ResultsEleven 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.ConclusionsThe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-1037) contains supplementary material, which is available to authorized users.
Highlights
Brassica napus (AACC) is self-compatible, its ancestor species Brassica rapa (AA) and Brassica oleracea (CC) are self-incompatible
S-1300 and 11 F1 hybrids, S-locus receptor kinase gene (SRK) genes and BnSCR-1300 transcripts were present at high levels, while expression of the
The recessive SC in eight accessions is caused by the loss of function of BnSCR-7 and BnSCR-6 in pollen
Summary
Brassica napus (AACC) is self-compatible, its ancestor species Brassica rapa (AA) and Brassica oleracea (CC) are self-incompatible. Expression and cloning of SRK and SCR genes and genetic analysis were carried out to dissect bases of recessive SC in B.napus. Brassica napus (AACC) is an amphidiploid species developed from B. rapa (AA) and B. oleracea (CC). B. rapa and B. oleracea are self-incompatible, but B. napus is self-compatible. Elucidating how self-incompatibility (SI) was lost and self-compatibility (SC) was acquired has profound consequences for understanding the origin of B. napus as well as trait changes during the evolutionary process of plant polyploidization. S-locus cysteine-rich protein (SCR) gene [3,4] (SP11, referred to as SCR hereafter). The SRK-SCR interaction is haplotype-specific and only occurs between the receptor and ligand encoded in the same S-locus haplotype [6,7,8]
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