A naturally occurring insertion in BrEMS1 confers genic male sterility in turnip (Brassica rapa ssp. rapa)

To identify genes associated with genic male sterility (GMS) that are useful for hybrid breeding in Brassica crops, we analyzed the “ms77B” strain, which is a spontaneous turnip GMS mutant derived from a cv. 77B population. Previously, we reported that the GMS phenotype of ms77B is caused by a single gene with sterility as the recessive trait. To identify the causative gene of GMS in ms77B, we performed bulked segregant and transcriptome analyses with high-throughput sequencing and identified BrEMS1 as the most likely candidate. BrEMS1 is a single-copy gene homologous to Arabidopsis thaliana EMS1/EXS, which is essential for anther development. The BrEMS1 gene of ms77B has a long insertion (1460 bp) in the coding sequence, and RNA sequencing revealed that the gene is not transcribed beyond the insertion site. The region that is not transcribed because of the insertion contains sequences that encode multiple leucine-rich repeats and a catalytic kinase domain. Furthermore, genotyping of an F2 population revealed a complete correlation between the insertion and the male sterility phenotype. Together, our results indicate that the male sterility phenotype of ms77B is due to a null mutation of BrEMS1, which is essential for anther development.