Expression profiles of a cytoplasmic male sterile line of Gossypium harknessii and its fertility restorer and maintainer lines revealed by RNA-Seq

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The Gossypium harknessii background cytoplasmic male sterility (CMS) system has been used in cotton hybrid breeding in China. However, the mechanism underlying pollen abortion and fertility restoration in CMS remains to be determined. In this study, we used RNA-seq to identify critical genes and pathways associated with CMS in G. harknessii based CMS lines (588A), the near isogenic restorer lines (588R), and maintainer lines (588B). We performed an assembly of 80,811,676 raw reads into 89,939 high-quality unigenes with an average length of 698 bp. Among these, 72.62% unigenes were annotated in public protein databases and were classified into functional clusters. In addition, we investigated the changes in expression of genes between 588A and 588B (588R); the RNA-seq data showed 742 differentially expressed genes (DEGs) between 588A and 588B and 748 DEGs between 588A and 588R. They were mainly down-regulated in 588A and most of them distributed in metabolic and biosynthesis of secondary metabolites pathways. Further analysis revealed 23 pollen development related genes were differentially expressed between 588A and 588B. Numerous genes associated with tapetum development were down-regulated in 588A, implicating tapetum dysplasia may be a key reason for pollen abortion in CMS lines. Also, among DEGs between 588A and 588R, we identified two PPR genes which were highly up-regulated in restorer line. This study may provide assistance for detailed molecular analysis and a better understanding of harknessii based CMS in cotton.