Identification of a male sterile gene Ms in Brassica rapa L

Male sterile lines are important for hybrid seed production in Brassica rapa . In our previous study, we obtained a multiple-allele inherited male sterile line of Chinese cabbage. To identify the male sterile gene Ms in B. rapa , we used B. rapa L. var. chinensis (‘AB03’; MsMs ) and B. rapa var. purpuraria (‘AB04’; Ms f Ms f ) as parents to construct an F 2 segregating population, and mapped the Ms gene on chromosome A07 between single sequence repeat (SSR) markers SSRY17 and SSRY22, which flank the gene at genetic distances of 0.11 cM and 0.31 cM, respectively. The interval between the two markers was 231.3 kb and comprised 21 genes. Whole-genome resequencing and sequence comparison revealed that only one gene, Bra015018 , harbored an insertion–deletion (InDel) in an exon in the mapped interval. This InDel led to premature termination of translation due to generation of the stop codon TGA. Bra015018 was homologous to AT1G34355 , which encoded a forkhead-associated (FHA) domain-containing protein that was related to plant growth and floral development. Genotyping revealed that male sterility was fully co-segregated with the InDel. qRT-PCR analysis showed that Bra015018 was specifically expressed in the stamen. Consequently, we predicted that Bra015018 was a candidate gene of Ms .