Abstract
The recessive genetic male sterility (RGMS) system plays a key role in the production of hybrid varieties in self-pollinating B. napus plants, and prevents negative cytoplasmic effects. However, the complete molecular mechanism of the male sterility during male-gametogenesis in RGMS remains to be determined. To identify transcriptomic changes that occur during the transition to male sterility in RGMS, we examined the male sterile line WSLA and male fertile line WSLB, which are near-isogenic lines (NILs) differing only in the fertility trait. We evaluated the phenotypic features and sterility stage using anatomical analysis. Comparative RNA sequencing analysis revealed that 3,199 genes were differentially expressed between WSLA and WSLB. Many of these genes are mainly involved in biological processes related to flowering, including pollen tube development and growth, pollen wall assembly and modification, and pollen exine formation and pollination. The transcript profiles of 93 genes associated with pollen wall and anther development were determined by quantitative RT-PCR in different flower parts, and classified into the following three major clades: 1) up-regulated in WSLA plants; 2) down-regulated in WSLA plants; and 3) down-regulated in buds, but have a higher expression in stigmas of WSLA than in WSLB. A subset of genes associated with sporopollenin accumulation were all up-regulated in WSLA. An excess of sporopollenin results in defective pollen wall formation, which leads to male sterility in WSLA. Some of the genes identified in this study are candidates for future research, as they could provide important insight into the molecular mechanisms underlying RGMS in WSLA.
Highlights
Brassica napus (L.) is an important worldwide source of vegetable oil and biofuel, and a nutrient-rich source of protein for livestock feed [1, 2]
A phenotypic characterization comparison of the WSLA and WSLB lines showed that the flowers and floral development appeared normal in WSLA (Fig 1A, 1C and 1E), but that the anthers and filaments of WSLA were shorter than those of the WSLB line (Fig 1B and 1F) and the stigmas and ovaries of WSLA were longer than those of WSLB (Fig 1D and 1F)
To characterize the cytology of the developing buds in WSLA and WSLB, we performed a histochemical analysis of stamens (< 4 mm) at stage 7 and stage 12, according to the previous report [45]
Summary
Brassica napus (L.) (rapeseed) is an important worldwide source of vegetable oil and biofuel, and a nutrient-rich source of protein for livestock feed [1, 2]. Pollen development and pollination affect the number of seeds formed and the quality and yield of crops. Male sterile plants are useful tools for hybrid seed production, as these plants are unable to self-pollinate and depend on pollen from another line for seed production. GMS, which offers advantages over CMS, such as complete male sterility and the absence of negative cytoplasmic effects, has been widely used in the production of hybrid rapeseed varieties [4]. Recessive genetic male sterility (RGMS), which is controlled by recessive gene(s), are easy to breed, since most lines can function as restorers. Two near-isogenic lines (NILs), WSLA and WSLB, the latter of which exhibits RGMS, have been used for rapeseed heterosis and Yuyou 27 (No 2012002), which is widely grown in China, is based on this system. Despite the commercial success of Yuyou 27, the mechanism underlying male sterility in this line was unclear
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