[Wan-Hsing Cheng] Nuclear-encoded CFM6 involved in mitochondrial intron splicing

Mitochondria derived from α-proteobacteria by endosymbiosis act as the cellular powerhouse in eukaryotic host cells. Most genes involved in regulation of mitochondrial gene expression were transferred to the nuclear genome during evolution. Therefore, functional mitochondria demand for various post transcriptional regulations from nuclear-encoded RNA binding proteins. In Arabidopsis, mitochondrial genome possesses 23 group II introns, which interrupt the expression of the genes encoding components of respiratory chain and mitochondrial ribosome. These degenerative group II introns have lost the ability to self-splice and require numerous nuclear-encoded proteins as splicing cofactors. Efficiently spliced these introns are important for the functional respiration and ATP synthesis. The research team in Dr. Wan-Hsing Cheng lab at the Institute of Plant and Microbial Biology found that CFM6 (CRM Family Member 6), a CRM-domain containing protein, functions specifically in the splicing of intron 4 of mitochondrial nad5. As nad5 encodes a subunit of mitochondrial respiratory complex I, splicing failure in cfm6 mutant led to the loss of complex I activity and to its improper assembly. Moreover, dysfunction of complex I resulted in abnormal mitochondrial morphology, stunted growth, curled leaves and sterility in the mutant plants. Taken together, our results indicate that CFM6 is a newly discovered splicing factor of nad5 transcript in Arabidopsis mitochondria. This study provides an important insight into the understanding the regulatory mechanisms of mitochondrial gene expression in plant cells. These findings are currently published in Plant Cell Physiol. The first author of this work is Dr. Wei-Chih Lin, a former Ph. D. student of IPMB-AS and Institute of Plant Biology-NTU Program.