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. Overall design: 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.