Fine mapping and candidate gene identification of a novel male-sterile gene Brmy1 in Chinese cabbage

Chinese cabbage ( Brassica rapa L. ssp. pekinensis ) is an economically valuable vegetable crop characterized by pronounced heterosis. Male-sterile lines are ideal materials for hybrid seed production, and identifying novel male-sterile genes is crucial for the development of elite germplasm and the improvement of breeding efficiency in Chinese cabbage. In this study, a spontaneous male-sterile mutant, my1 , was obtained from the Chinese cabbage inbred line MRTY. Cytological observations showed that premature tapetal degeneration and abnormal microspore development resulted in pollen abortion in the my1 mutant. Transcriptome analysis revealed that the my1 phenotype may be associated with redox regulation and hormone signaling pathways. Genetic analysis showed that a recessive gene controlled the my1 trait. Fine mapping identified BrRBOHJ , encoding a respiratory burst oxidase, as a strong candidate gene for my1 . Multiple sequence variations were identified in the promoter and coding regions of BrRBOHJ in the my1 mutant, and its expression was barely detectable in my1 anthers compared with WT. BrRBOHJ was predominantly expressed in floral tissues, and reduced ROS levels were observed in my1 anthers. This study suggests that BrRBOHJ is associated with male sterility by affecting tapetal and microspore development, and provides a valuable male-sterile genetic resource for heterosis utilization in Chinese cabbage.