Identification and characterization of rice circular RNAs responding to Xanthomonas oryzae pv. oryzae invasion.

Emerging role of circular RNAs (circRNAs) in various biological processes have advanced our knowledge of transcriptional and post-transcriptional gene regulation. To date, no research has been conducted to explore their roles in the rice- Xanthomonas oryzae pv. oryzae (Xoo) interaction. Therefore, we identified 3517 circRNAs from the highly virulent Xoo strain PXO99A-infected rice leaves using the ribosomal RNA (rRNA) depleted RNA-sequencing technique coupled with the CIRI2 and CIRCexplorer2 pipeline. Characterization analyses showed that these circRNAs were distributed across the whole genome of rice, and most circRNAs arised from exons (85.13 %), ranged from 200 bp to 1000 bp and were with a non-canonical GT/AG (including CT/AC equivalent) splicing signal. Functional annotation and enrichment analysis of the host genes that produced the DEcircRNAs suggested that these identified circRNAs might play an important role in reprogramming rice responses to PXO99A invasion, mainly by mediating photorespiration, chloroplast, peroxisome and diterpenoid biosynthesis. Moreover, 31 differentially expressed circRNAs (DEcircRNAs) were predicted to act as miRNA decoys in rice. The expression profile of 4 DEcircRNAs were validated by RT-qPCR with divergent primers, and the back-splicing sites of seven DEcircRNAs were verified by PCR analysis and Sanger sequencing. Collectively, these results inferred a potential functional role of circRNAs in the regulation of rice immunity and provide novel clues for revealing the molecular mechanisms of rice-PXO99A interaction.