Identification and characterization of circular RNAs involved in the fertility stability of cotton CMS-D2 restorer line under heat stress.

Background: As a vital type of noncoding RNAs, circular RNAs (circRNAs) play important roles in plant growth and development and stress response. However, little is known about the biological roles of circRNAs in regulating the stability of male fertility restoration for cytoplasmic male sterility (CMS) conditioned by Gossypium harknessii cytoplasm (CMS-D2) cotton under high-temperature (HT) stress. Results: In this study, RNA-sequencing and bioinformatics analysis were performed on pollen grains of isonuclear alloplasmic near-isogenic restorer lines NH [N(Rf1rf1)] and SH [S(Rf1rf1)] with obvious differences in fertility stability under HT stress at two environments. A total of 967 circRNAs were identified, with 250 differentially expressed under HT stress. We confirmed the back-splicing sites of eight selected circRNAs using divergent primers and Sanger sequencing. Tissue-specific expression patterns of five differentially expressed circRNAs (DECs) were also verified by RT-PCR and qRT-PCR. Functional enrichment and metabolic pathway analysis revealed that the parental genes of DECs were significantly enriched in fertility-related biological processes such as pollen tube guidance and cell wall organization, as well as the Pentose and glucuronate interconversions, Steroid biosynthesis, and N-Glycan biosynthesis pathways. Moreover, we also constructed a putative circRNA-mediated competing endogenous RNA (ceRNA) network consisting of 21 DECs, eight predicted circRNA-binding miRNAs, and their corresponding 22 mRNA targets, especially the two ceRNA modules circRNA346-miR159a-MYB33 and circRNA484-miR319e-MYB33, which might play important biological roles in regulating pollen fertility stability of cotton CMS-D2 restorer line under HT stress. Conclusions: Through systematic analysis of the abundance, characteristics and expression patterns of circRNAs, as well as the potential functions of their parent genes, our findings suggested that circRNAs and their mediated ceRNA networks acted vital biological roles in cotton pollen development, and might be also essential regulators for fertility stability of CMS-D2 restorer line under heat stress. This study will open a new door for further unlocking complex regulatory mechanisms underpinning the fertility restoration stability for CMS-D2 in cotton. [ABSTRACT FROM AUTHOR]