Fine mapping and cloning of the sterility gene Bra2Msin non-heading Chinese cabbage (Brassica rapassp. chinensis)

The application of a male-sterile line is an ideal approach for hybrid seed production in non-heading Chinese cabbage (Brassica rapassp. chinensis). However, the molecular mechanisms underlying male sterility in B. rapaare still largely unclear. We previously obtained the natural male sterile line WS24-3 of non-heading Chinese cabbage and located the male sterile locus, Bra2Ms, on the A2 chromosome. Cytological observations revealed that the male sterility of WS24-3 resulted from disruption of the meiosis process during pollen formation. Fine mapping of Bra2Msdelimited the locus within a physical distance of about 129 kb on the A2 chromosome of B. rapa. The Bra039753gene encodes a plant homeodomain (PHD)-finger protein and is considered a potential candidate gene for Bra2Ms. Bra039753was significantly downregulated in sterile line WS24-3 compared to the fertile line at the meiotic anther stage. Sequence analysis of Bra039753identified a 369 bp fragment insertion in the first exon in male sterile plants, which led to an amino acid insertion in the Bra039753 protein. In addition, the 369 bp fragment insertion was found to cosegregate with the male sterility trait. This study identified a novel locus related to male sterility in non-heading Chinese cabbage, and the molecular marker obtained in this study will be beneficial for the marker-assisted selection of excellent sterile lines in non-heading Chinese cabbage and other Brassicacrops.