Identification and Characterization of Circular RNAs in Brassica rapa in Response to Plasmodiophora brassicae

Plasmodiophora brassicae is a soil-borne pathogen that attacks the roots of cruciferous plants and causes clubroot disease. CircRNAs are noncoding RNAs, widely existing in plant and animal species. Although knowledge of circRNAs has been updated continuously and rapidly, information about circRNAs in the regulation of clubroot disease resistance is extremely limited in Brassica rapa. Here, Chinese cabbage (BJN 222) containing clubroot resistance genes (CRa) against P. brassicae Pb4 was susceptible to PbE. To investigate the mechanism of cicRNAs responsible for clubroot disease resistance in B. rapa, circRNA-seq was performed with roots of 'BJN 222' at 0, 8, and 23 days post-inoculated (dpi) with Pb4 and PbE. A total of 231 differentially expressed circRNAs were identified between the groups. Based on the differentially expressed circRNAs, the circRNA-miRNA-mRNA network was constructed using the target genes directly or indirectly related to plant resistance. Upregulated novel_circ_000495 suppressed the expression of miR5656-y, leading to the upregulation of Bra026508, which might cause plant resistance. Our results provide new insights into clubroot resistance mechanisms and lay a foundation for further studies exploring complex gene regulation networks in B. rapa.

Automated summary

In this study, circRNA-seq was performed to investigate the role of circRNAs in clubroot disease resistance in Brassica rapa. Differentially expressed circRNAs were identified and a circRNA-miRNA-mRNA network was constructed. One upregulated circRNA was found to suppress the expression of a miRNA and upregulate a gene, possibly leading to plant resistance. These findings provide new insights into clubroot resistance mechanisms and lay the foundation for further studies on complex gene regulation networks in B. rapa.