MORF2 is a key effector of plastidial retrograde signaling for stress response and plant morphogenesis beyond RNA editing

Multiple Organellar RNA Editing Factor 2 (MORF2) was previously discovered to be involved in chloroplast RNA editing. However, the albino and unviable phenotype of the T-DNA insertion mutants, morf2-1 and morf2-2, seems to be inconsistent with many other viable chloroplast RNA editing mutants, suggesting that MORF2 has other biological functions beyond RNA editing. To discover new biological functions of MORF2, we applied a novel inducible Clustered Regularly Interspaced Short Palindromic Repeat interference (iCRISPRi) approach to quantitatively monitor early transcriptome changes upon the gradient reduction of MORF2 by RNA-Seq analysis. P1-12 is an Arabidopsis transgenic line in a Col-0 background transformed with a dCas9-KRAB transcription repressor driven by a Dexamethasone (Dex)-inducible promoter and a sgRNA gene containing a protospacer specific to -2 to +18 nt of the transcription start site of MORF2. Upon 0.025 microM and 0.25 microM Dex treatment, dCas9-KRAB expression is induced at different levels resulting in a gradient suppression of MORF2 in P1-12. KRAB indicates the Arabidopsis transgenic line in a Col-0 background only transformed with a dCas9-KRAB transcription repressor driven by a Dex-inducible promoter.