Identification and Analysis of MS5 ^d: A Gene That Affects Double-Strand Break (DSB) Repair during Meiosis I in Brassica napus Microsporocytes

Here, we report the identification of the Brassica-specific gene MS5 ^d, which is responsible for male sterility in Brassica napus. The MS5 ^d gene is highly expressed in the microsporocyte and encodes a protein that localizes to the nucleus. Light microscopy analyses have demonstrated that the MS5 ^d gene affects microsporocyte meiosis in the thermosensitive genic male sterility line TE5A. Sequence comparisons and genetic complementation revealed a C-to-T transition in MS5 ^d, encoding a Leu-to-Phe (L281F) substitution and causing abnormal male meiosis in TE5A. These findings suggest arrested meiotic chromosome dynamics at pachytene. Furthermore, immunofluorescence analyses showed that double-strand break (DSB) formation and axial elements were normal but that DSB repair and spindle behavior were aberrant in TE5A meiocytes. Collectively, our results indicate that MS5 ^d likely encodes a protein required for chromosomal DSB repair at early stages of meiosis in B. napus.