MS5 Mediates Early Meiotic Progression and Its Natural Variants May Have Applications for Hybrid Production in Brassica napus

Abstract

During meiotic prophase I, chromatin undergoes dynamic changes to establish a structural basis for essential meiotic events. However, the mechanism that coordinates chromosome structure and meiotic progression remains poorly understood in plants. Here, we characterized a spontaneous sterile mutant MS5 b MS5 b in oilseed rape (Brassica napus) and found its meiotic chromosomes were arrested at leptotene. MS5 is preferentially expressed in reproductive organs and encodes a Brassicaspecific protein carrying conserved coiled-coil and DUF626 domains with unknown function. MS5 is essential for pairing of homologs in meiosis, but not necessary for the initiation of DNA double-strand breaks. The distribution of the axis elementassociated protein ASY1 occurs independently of MS5, but localization of the meiotic cohesion subunit SYN1 requires functional MS5. Furthermore, both the central element of the synaptonemal complex and the recombination element do not properly form in MS5 b MS5 b mutants. Our results demonstrate that MS5 participates in progression of meiosis during early prophase I and its allelic variants lead to differences in fertility, which may provide a promising strategy for pollination control for heterosis breeding.

Identification and Analysis of MS5d: A Gene That Affects Double-Strand Break (DSB) Repair during Meiosis I in Brassica napus Microsporocytes

“…Xin et al (2016) demonstrated that the loss of the MS5 a gene resulted in abortive meiosis in the B. napus line Rs1046A; the phenotypic defects in microsporocytes resembled those of TE5A. We found that ms5 d and MS5 a , both of which originated from Bra018456, exhibit the same sequences.…”

“…Functional divergence of genes from common ancestors can result in three distinct evolutionary fates: gene silencing with negative mutations, or pseudogenization; partition of ancestral function, or subfunctionalization; and acquisition of new function, or neofunctionalization (Force et al, 1999; Conant and Wolfe, 2008; Liu and Adams, 2010). Thus, we propose that MS5 d was derived from the neofunctionalization of its ancestor, whereas MS5 b originated from gene silencing with negative mutations of the same ancestor of MS5 d (Xin et al, 2016). These findings provide an interesting system in which to study the divergence of functional genes in paleoploid Brassica species.…”

“…Male sterility is the most effective and economical pollination control system for utilization of heterosis in rapeseed breeding. Previous studies have described the genetic male gene MS5 , which has three different alleles ( MS5 a , MS5 b , and MS5 c ) that lead to observed differences in fertility in Brassica napus (Lu et al, 2013; Xin et al, 2016). Plants carrying the BnMs5 b BnMs5 b or BnMs5 b BnMs5 c genotypes were sterile, whereas plants homozygous for the BnMs5 c or BnMs5 a allele were fertile (Lu et al, 2013).…”

“…Relative to the sequence of MS5 a , an 8,115-bp Mutator-like transposable element (MULE) insertion was detected in MS5 b . Loss of MS5 a function had no effect on normal meiotic chromosome configuration at leptotene, but it resulted in abnormal chromosome morphology and cytokinesis during the following stages in MS5 b MS5 b microspore mother cells (MMCs; Xin et al, 2016). Functional analyses demonstrated that MS5 was essential for homologous pairing in meiosis but not for the initiation of DNA DSBs.…”

“…Functional analyses demonstrated that MS5 was essential for homologous pairing in meiosis but not for the initiation of DNA DSBs. Further analysis revealed that different expression levels of MS5 and its allelic variants caused differences in fertility (Xin et al, 2016). …”