Genome-Wide Identification and Characterization of Circular RNAs Involved in High Night Temperature Stress at the Filling Stage of Rice.

High night temperatures seriously threaten the normal growth of rice, especially during the filling stage. Studies have shown that circRNAs play crucial roles in regulating plant stress response. Here, 3670 circRNAs were identified from a rice heat-tolerant line and a heat-sensitive line under high night temperature stress at the filling stage. 546 circRNAs showed conservation among the plant species, and 396 circRNAs owned potential protein translation abilities. The expression of the circRNAs was verified using PCR and sequencing. Further, 103 and 118 circRNAs were separately found to be differentially expressed in these two rice lines. The regulatory relationship of circRNA-parental gene pairs and the circRNA-miRNA-mRNA ceRNA network was constructed to reveal the function of these circRNAs. Functional enrichment analysis indicated that these circRNAs are involved in heat stress-related biological processes and metabolic pathways. Finally, 28 circRNAs showed significant relative expression changes between the heat-tolerant line and heat-sensitive line, being possibly involved in the differential heat sensitivity phenotype. Sixteen circRNA-parental gene pairs and nine circRNA-20 miRNA-242 mRNA ceRNA regulatory networks were additionally obtained and partially validated by qRT-PCR. Functional analysis of these regulated genes indicated that high night temperature-responsive circRNAs were involved in various heat-related biological processes, such as transcription regulation, nutrient metabolism, stress response, hormone regulation, redox processes, chloroplast regulation, and protein folding, which are discussed in detail here. This study provides new insights into the potential role of circRNAs responding to high night temperature stress at the filling stage of rice and provides new ideas for rice heat-tolerance breeding.