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Map-based cloning reveals the complex organization of the BnRf locus and leads to the identification of BnRf b, a male sterility gene, in Brassica napus

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Key message

Sequencing of BAC clones reveals the complex organization of the BnRf locus and allowed us to clone BnRf b , which encodes a nucleus-localized chimeric protein BnaA7.mtHSP70-1-like.


The male sterility in an extensively used genic male sterility (GMS) line (9012A) in Brassica napus was regarded to be conferred by BnMs3/Bnms3 and the multiallelic BnRf locus including three alleles. We previously mapped BnRf to a 13.8 kb DNA fragment on the B. napus chromosome A7. In the present study, we isolated bacterial artificial chromosome clones individually covering the restorer allele BnRf a and the male-sterile allele BnRf b, and revealed that the candidate regions of BnRf a and BnRf b show complex structural variations relative to the maintainer allele BnRf c. By analyzing the recombination events and the newly developed markers, we delimited BnRf a to a 35.9 kb DNA fragment that contained seven predicted open-reading frames (ORFs). However, genetic transformation of the ORF G14 from both the male-sterile and restorer lines into wild-type Arabidopsis plants led to a stable male-sterile phenotype matching a 9012A-derived GMS line (RG206A); moreover, the male sterility caused by G14 could be fully recovered by the restorer gene BnMs3. These facts indicate that BnRf b corresponds to G14 while BnRf a likely associates with another flanking ORF. G14 encodes a nucleus-localized chimeric protein designated as BnaA7.mtHSP70-1-like. Ectopic expression of G14 in Arabidopsis negatively regulates some vital genes responsible for tapetum degeneration, and delayed programmed cell death of tapetum and led to the developmental arrest of tetrads. Our work not only presents new insights on the hereditary model of sterility control but also lays a solid foundation for dissecting the molecular basis underlying male sterility and restoration in 9012A.

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Special thanks are shown to Dr Meizhong Luo for help in construction of the BAC clone library. This work was funded by the National Natural Science Foundation of China (No. 31070279, 31170166 and 31201267) and China Postdoctoral Science Foundation (2013M531706).

Author contribution statement

ZD conducted most of the experiments, including the fine mapping, BAC clone screening, genetic transformation, expression analysis and evolutionary analysis. XL and ZW characterized the cytological and histochemical phenotypes of anther development of B. napus and Arabidopsis plants, including preparation of cross sections, TUNEL assays, lipid accumulation, and callose staining. LW, FD, YF and FC prepared mapping populations. GY initiated the project. DH designed and supervised the study, analyzed the data, and wrote the paper.

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Correspondence to Dengfeng Hong.

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The experiments comply with the current laws of the countries in which they were performed.

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Communicated by I. Parkin.

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Deng, Z., Li, X., Wang, Z. et al. Map-based cloning reveals the complex organization of the BnRf locus and leads to the identification of BnRf b, a male sterility gene, in Brassica napus . Theor Appl Genet 129, 53–64 (2016). https://doi.org/10.1007/s00122-015-2608-8

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  • Bacterial Artificial Chromosome
  • Male Sterility
  • Bacterial Artificial Chromosome Clone
  • Bacterial Artificial Chromosome Library
  • Tapetal Cell