Abstract
Crosses that lead to heterosis have been widely used in the rapeseed (Brassica napus L.) industry. Cytoplasmic male sterility (CMS)/restorer-of-fertility (Rf) systems represent one of the most useful tools for rapeseed production. Several CMS types and their restorer lines have been identified in rapeseed, but there are few studies on the mechanisms underlying fertility restoration. Here, we performed morphological observation, map-based cloning, and transcriptomic analysis of the F2 population developed by crossing the CMS line WNJ01A with its restorer line Hui01. Paraffin-embedded sections showed that the sporogenous cell stage was the critical pollen degeneration period, with major sporogenous cells displaying loose and irregular arrangement in sterile anthers. Most mitochondrial electron transport chain (mtETC) complex genes were upregulated in fertile compared to sterile buds. Using bulked segregant analysis (BSA)-seq to analyze mixed DNA pools from sterile and fertile F2 buds, respectively, we identified a 6.25 Mb candidate interval where Rfw is located. Using map-based cloning experiments combined with bacterial artificial chromosome (BAC) clone sequencing, the candidate interval was reduced to 99.75 kb and two pentatricopeptide repeat (PPR) genes were found among 28 predicted genes in this interval. Transcriptome sequencing showed that there were 1679 DEGs (1023 upregulated and 656 downregulated) in fertile compared to sterile F2 buds. The upregulated differentially expressed genes (DEGs) were enriched in the Kyoto Encyclopedia of Genes and Genomes (KEGG) lysine degradation pathway and phenylalanine metabolism, and the downregulated DEGs were enriched in cutin, suberine, and wax biosynthesis. Furthermore, 44 DEGs were involved in pollen and anther development, such as tapetum, microspores, and pollen wall development. All of them were upregulated except a few such as POE1 genes (which encode Pollen Ole e I allergen and extensin family proteins). There were 261 specifically expressed DEGs (9 and 252 in sterile and fertile buds, respectively). Regarding the fertile bud-specific upregulated DEGs, the ubiquitin–proteasome pathway was enriched. The top four hub genes in the protein–protein interaction network (BnaA09g56400D, BnaA10g18210D, BnaA10g18220D, and BnaC09g41740D) encode RAD23d proteins, which deliver ubiquitinated substrates to the 26S proteasome. These findings provide evidence on the pathways regulated by Rfw and improve our understanding of fertility restoration.
Highlights
Rapeseed (Brassica napus L.) is one of the most important oil crops worldwide
After using The Arabidopsis Information Resource (TAIR) database to annotate the Differentially expressed genes (DEGs), we discovered that 44 DEGs (35 upregulated and 9 downregulated in fertile buds) were related to anther and pollen development (Supplementary Table 6)
The WNJ01A Cytoplasmic male sterility (CMS) line displayed a complete pollen abortion phenotype, and its fertility could be restored by the restorer line Hui01
Summary
Rapeseed (Brassica napus L.) is one of the most important oil crops worldwide. Crosses that lead to heterosis, involving significantly increased seed yield, have been widely used for rapeseed production in the past decades (Morrison et al, 2016; Shen et al, 2017). Plant CMS is generally caused by new chimeric open reading frames (ORFs) in the mitochondrial genome, and they are usually generated through mitochondrial genome rearrangement (Tang H. et al, 2017) These novel ORFs are usually homologous or co-transcribed with the genes encoding proteins of the mitochondrial electron transport chain (mtETC) complexes or ATP synthase, so these systems do not function normally (Bohra et al, 2016). Most cloned plant Rf genes encode pentatricopeptide repeat (PPR)-containing proteins (Kubo et al, 2020). These proteins are RNA-binding factors that participate in mRNA processing after transport to a mitochondrion (Schmitz-Linneweber and Small, 2008). During the fertility restoration of CMS, they downregulate sterility genes by cleaving their transcripts or inhibiting their translation (Gaborieau et al, 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
