Peptidyl-prolyl isomerase Cyclophilin 71 promotes SERRATE phase separation and miRNA processing in Arabidopsis [mRNA-Seq]

MicroRNAs (miRNAs) play an important role in gene regulation. In Arabidopsis thaliana, mature miRNAs are processed from primary miRNA transcripts by Dicing complex, which contains DCL1, SE and HYL1 and forms nuclear dicing bodies (D-bodies) through SE phase separation. Here we report that Cyclophilin 71 (CYP71), a peptidyl-prolyl isomerase (PPIase), positively regulates miRNA processing. We show that CYP71 directly interacts with SE and enhances its phase separation, thereby promoting the formation of D-body and increasing the activity of Dicing complex. We further show that the PPIase activity is important for the function of CYP71 in miRNA production. Our findings reveal orchestration of miRNA processing by a cyclophilin protein and suggest the involvement of proline cis-trans isomerization, a structural mechanism, in SE phase separation and miRNA processing. To evaluate the impact of CYP71 mutations on miRNA and miRNA target gene expression profile, we performed small RNA-seq and mRNA-seq in triplicate using 2-week-old Col-0, cyp71-2, cyp71-3 seedlings.