An mTERF domain protein functions in group II intron splicing in maize chloroplasts

Area of Science:

• Plant molecular biology
• Chloroplast gene expression
• RNA splicing mechanisms

Background:

• Mitochondrial transcription termination factor (mTERF) proteins are nucleic acid binders involved in gene expression.
• While mTERF functions are known in metazoans, their roles in plants, particularly in chloroplasts, remain largely uncharacterized.
• Plant mTERF proteins are numerous and target either mitochondria or chloroplasts, suggesting diverse roles.

Purpose of the Study:

• To investigate the molecular function of the maize mTERF protein, Zm-mTERF4, in chloroplasts.
• To determine if Zm-mTERF4 plays a role in RNA processing events within the chloroplast.
• To link the function of Zm-mTERF4 to observed plant developmental phenotypes.

Main Methods:

• Co-immunoprecipitation assays to identify Zm-mTERF4 interacting partners.
• Analysis of chloroplast intron splicing in wild-type and Zm-mterf4 mutant maize lines.
• Characterization of Zm-mTERF4 protein complexes using size-exclusion chromatography.
• Phenotypic analysis of Zm-mterf4 mutants, focusing on plastid ribosome content.

Main Results:

• Zm-mTERF4 was shown to promote the splicing of group II introns in chloroplasts.
• Splicing of specific chloroplast introns, including trnI-GAU, trnA-UGC, and rpl2, was impaired in Zm-mterf4 mutants.
• Zm-mTERF4 interacts with chloroplast introns and forms high molecular weight complexes with known splicing factors.
• Mutations in Zm-mTERF4 led to a loss of plastid ribosomes, correlating with splicing defects.

Conclusions:

• Zm-mTERF4 functions as a chloroplast RNA splicing factor, specifically promoting group II intron splicing.
• The findings expand the known functions of the mTERF protein family to include chloroplast RNA splicing.
• The conserved role of Zm-mTERF4 orthologs in chloroplast RNA splicing likely explains physiological defects observed in related plant mutants.