Mapping of the male sterile mutant gene ftms in Brassica rapa L. ssp. pekinensis via BSR-Seq combined with whole-genome resequencing

Key message A male sterile mutant was created by 60 Co γ-rays of microspores isolated from Chinese cabbage DH line ‘FT’. A candidate gene for the male sterile trait was identified as Bra010198 . Male sterility is used for hybrid seed production in Chinese cabbage. In this study, we derived a male sterile mutant ( ftms ) from Chinese cabbage DH line ‘FT’ by irradiating microspores with 60 Co γ-rays and realized the rapid trait transformation from male fertility to sterility for creating valuable breeding materials. Genetic analysis indicated that the male sterile trait is controlled by a single recessive nuclear gene, ftms . Microspore development in mutant ftms was aborted at the tetrad stage and associated with severely retarded degeneration and vacuolation of tapetum. Using BSR-seq analysis, the candidate region for ftms was mapped on chromosome A05. A large F 2 population was created, and the region was narrowed to approximately 1.7-Mb between markers Indel20 and Indel14 via linkage analysis. The recombination frequency was extremely suppressed because the region was located on the chromosome A05 centromere. Whole-genome resequencing of mutant ftms and wild-type ‘FT’ aligned only one nonsynonymous SNP to Bra010198 ; this gene is a homolog of Arabidopsis KNS4/UPEX1, which encodes a putative β -(1,3)-galactosyltransferase that controls pollen exine development. Comparative sequencing verified the SNP position on the fifth exon of Bra010198 in mutant ftms . Further genotyping revealed that the male sterile phenotype was fully co-segregated with this SNP. Quantitative real-time PCR indicated that Bra0101918 specifically expressed in stamen. The data presented herein suggested that Bra010198 is a strong candidate gene for ftms . Hence, we developed a male sterile line for potential application in breeding and expanded the knowledge about the molecular mechanism underlying male sterility in Chinese cabbage.