Comparison of tolerant and susceptible cultivars revealed the roles of circular RNAs in rice responding to salt stress

As a newly characterized class of noncoding RNAs, circular RNAs (circRNAs) have been identified in many plant species, and play important roles in plant stress responses. However, little is known about how salt stress mediates the expression of circRNAs in rice. In this study, we identified circRNAs from root tissues of salt-susceptible recipient cultivar 93-11 and salt-tolerant introgression line 9L136. A total of 190 circRNAs were identified. Among them, 93 circRNAs were differentially expressed under salt stress in 93-11 (36 up- and 57 down-regulated) and 95 in 9L136 (46 up- and 49 down-regulated). Salt stress significantly decreased the average expression level of circRNAs in 93-11, but circRNA expression levels were slightly increased in 9L136, suggesting that circRNAs had different response patterns in these two cultivars. Function annotation and enrichment analysis indicated that, through cis-regulation and circRNA-miRNA-mRNA network regulation, those induced circRNAs were commonly involved in transcription, signal transduction, ion transportation, and secondary metabolism. Compared to 93-11, salt-induced circRNAs in line 9L136 targeted more stress response genes participating in transcription regulation, ion transportation, and signal transduction, which may contribute to the salt tolerance of 9L136. Summarily, this study revealed the common response of rice circRNAs to salt stress, and the possible circRNA-related salt tolerance mechanisms of 9L136.