MORF2 tightly associates with MORF9 to regulate chloroplast RNA editing in Arabidopsis.

RNA editing in chloroplasts and mitochondria is performed by hypothetical editosomes. The MORF family proteins are essential components of these editosomes. In Arabidopsis, MORF2 and MORF9 are involved in the editing of most sites in chloroplasts. In this work, we performed immunoprecipitation and mass spectrometry assays of transgenic lines expressing MORF2-4xMYC and MORF9-4xMYC to identify interacting proteins. We found that MORF2 and MORF9 are present in the same complex. Blue-Native PAGE analysis of chloroplast protein complexes also revealed that both MORF2 and MORF9 are part of a complex of approximately 140 kDa, suggesting the existence of tight MORF2-MORF9 interaction in chloroplasts. The editing of ndhD-1 (ndhD-C2) site was reported to be blocked in both morf2 and morf9. RNA immunoprecipitation assays showed that MORF2 and MORF9 are tightly associated with the editing site of ndhD-1. However, in an RNA-EMSA assay MORF2 and MORF9 could not directly bind to transcripts harboring the editing site of ndhD-1. Taken together, these results indicate that the MORF2-MORF9 heterodimer is the core members of editosomes in chloroplasts, while they are not responsible for RNA editing site recognition.