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

Area of Science:

• Plant molecular biology
• Organelle gene expression
• RNA biology

Background:

• RNA editing in chloroplasts and mitochondria is essential for proper gene function.
• The MORF (Mitochondrial and Organellar RNA editing Factor) family proteins are key components of the hypothetical editosomes responsible for this process.
• MORF2 and MORF9 are known to be involved in editing most sites in Arabidopsis chloroplasts.

Purpose of the Study:

• To identify interacting proteins within chloroplast editosomes.
• To elucidate the role of MORF2 and MORF9 in RNA editing.
• To investigate the interaction between MORF2 and MORF9.

Main Methods:

• Immunoprecipitation and mass spectrometry assays using transgenic Arabidopsis lines expressing MORF2-4xMYC and MORF9-4xMYC.
• Blue-Native PAGE analysis of chloroplast protein complexes.
• RNA immunoprecipitation and RNA electrophoretic mobility shift assays (RNA-EMSA).

Main Results:

• MORF2 and MORF9 co-immunoprecipitate, indicating they exist in the same complex.
• Blue-Native PAGE reveals MORF2 and MORF9 are part of a ~140 kDa complex in chloroplasts.
• MORF2 and MORF9 are tightly associated with the ndhD-1 RNA editing site but do not directly bind the transcript.
• Editing of the ndhD-1 site is impaired in both morf2 and morf9 mutants.

Conclusions:

• The MORF2-MORF9 heterodimer represents a core component of chloroplast editosomes.
• These MORF proteins are essential for RNA editing activity.
• MORF2 and MORF9 are not directly responsible for recognizing RNA editing sites, suggesting other factors are involved in target selection.