Exonic Circular RNAs Are Involved in Arabidopsis Immune Response Against Bacterial and Fungal Pathogens and Function Synergistically with Corresponding Linear RNAs.

Circular RNAs (circRNAs) are a group of covalently closed RNAs, and their biological function is largely unknown. In this study, we focused on circRNAs that are generated from exon back-splicing (exonic circRNAs). The linear RNA counterparts encode functional proteins so that we can compare and investigate the relationship between circular and linear RNAs. We compared circRNA expression profiles between untreated and -infected and identified and experimentally validated differentially expressed exonic circRNAs by multiple approaches. We found that exonic circRNAs are preferentially enriched in biological processes that associate with biotic and abiotic stress responses. We discovered that circR194 and circR4022 are involved in plant response against infection, whereas circR11208 is involved in response against infection. Intriguingly, our results indicate that these exonic circRNAs function synergistically with their corresponding linear RNAs. Furthermore, circR4022 and circR11208 also play substantial roles in tolerance to salt stress. This study extends our understanding of the molecular functions of plant circRNAs.