Control of organelle gene expression by the mitochondrial transcription termination factor mTERF22 in Arabidopsis thaliana plants

Abstract

Mitochondria are key sites for cellular energy metabolism and are essential to cell survival. As descendants of eubacterial symbionts (specifically α-proteobacteria), mitochondria contain their own genomes (mtDNAs), RNAs and ribosomes. Plants need to coordinate their energy demands during particular growth and developmental stages. The regulation of mtDNA expression is critical for controlling the oxidative phosphorylation capacity in response to physiological or environmental signals. The mitochondrial transcription termination factor (mTERF) family has recently emerged as a central player in mitochondrial gene expression in various eukaryotes. Interestingly, the number of mTERFs has been greatly expanded in the nuclear genomes of plants, with more than 30 members in different angiosperms. The majority of the annotated mTERFs in plants are predicted to be plastid- or mitochondria-localized. These are therefore expected to play important roles in organellar gene expression in angiosperms. Yet, functions have been assigned to only a small fraction of these factors in plants. Here, we report the characterization of mTERF22 (At5g64950) which functions in the regulation of mtDNA transcription in Arabidopsis thaliana. GFP localization assays indicate that mTERF22 resides within the mitochondria. Disruption of mTERF22 function results in reduced mtRNA accumulation and altered organelle biogenesis. Transcriptomic and run-on experiments suggest that the phenotypes of mterf22 mutants are attributable, at least in part, to altered mitochondria transcription, and indicate that mTERF22 affects the expression of numerous mitochondrial genes in Arabidopsis plants.

The PPR-related splicing cofactor MSP1/EMB1025 protein, encoded by At4g20090, encode an essential protein that is required for the splicing ofnad1intron 1 and for the biogenesis of complex I in Arabidopsis mitochondria

“…In-vivo localizations by GFP-fusion protein assays were performed essentially as described previously (Shevtsov et al 2018b). A 450 nucleotide fragment of the 5'-terminus of MSP1 (At4g20090) was fused in-frame to eGFP, and cloned into pSAT6 vector (Tzfira et al 2005).…”

“…The cells were harvested by centrifugation, resuspended to a final concentration equivalent to A600 ~ 1.0 O.D. in transformation buffer (Shevtsov, et al 2018b). For localization analyses, 3~5 young leaves of N. benthamiana (4 to 6 week-old) were infiltrated with the Agrobacterium suspension using a 1 mL syringe (abaxial side, without a needle).…”

“…RNA extraction and analysis was performed essentially as described previously (Cohen, et al 2014, Keren et al 2011, Shevtsov, et al 2018b, Sultan, et al 2016, Zmudjak, et al 2013. In brief, RNA was prepared from 50 mg seedlings grown on MS-agar plates supplemented with 1% sucrose, following standard TRIzol Reagent protocols (Ambion, Thermo Fisher Scientific) with additional phenol/chloroform extraction procedure.…”

“…Oxygen consumption (i.e. O2 uptake) measurements were performed with a Clarke-type oxygen electrode, and the data feed was collected by Oxygraph-Plus version 1.01 software (Hansatech Instruments), as described previously (Shevtsov, et al 2018b). The electrode was calibrated with oxygen-saturated water and by the addition of excess sodium dithionite for complete depletion of the oxygen in water housed in the electrode chamber.…”

CyMIRA: The Cytonuclear Molecular Interactions Reference forArabidopsis

“…Mitochondrial transcription termination factors (mTERFs) are another sizeable family of organelle-targeted nucleic-acid binding proteins (Shevtsov, et al 2018). Similar to how we handled PPRs, we defined mTERFs as their own subcategory within the transcription and transcript maturation category, even though many individual mTERF genes await functional characterization.…”