Molecular mechanisms underpinning the multiallelic inheritance of <i>MS5</i> in <i>Brassica napus</i>

Abstract

SUMMARY The Brassica ‐specific gene MS5 mediates early meiotic progression, and its allelic variants contribute to a valuable genic male sterility three‐line hybrid production system in rapeseed ( Brassica napus L.). However, the underlying mechanisms of its triallelic inheritance are poorly understood. Herein, we show that the restorer allele MS5 a and the maintainer allele MS5 c are both necessary for male fertility in B. napus . The functional divergence of MS5 a and MS5 c is strongly related to sequence variations in their coding regions and less strongly to their promoter regions. The male‐sterile allele MS5 b encodes a chimeric protein containing only the complete MS5 coiled‐coil (CC) domain, having lost the MS5 superfamily domain. Both MS5 a and MS5 c can form homodimers in the nucleus via the CC domain. MS5 b can interact competitively with MS5 a or MS5 c to form non‐functional heterodimers. Owing to the close transcript levels of MS5 b and MS5 c in MS5 b MS5 c , these heterodimers induced a dominant‐negative effect of MS5 b on MS5 c , resulting in a male‐sterile phenotype. The extremely high transcript abundance of MS5 a maintains sufficient MS5 a homodimers in MS5 a MS5 b , causing the recovery of male sterility. These findings provide substantial genetic and molecular evidence to improve our understanding of the mechanisms underlying the multiallelic inheritance of MS5 , and enable the construction of a solid foundation for improved use of the MS5 ‐controlled GMS system in Brassica species.