Arabidopsis mTERF9 protein promotes chloroplast ribosomal assembly and translation by establishing ribonucleoprotein interactions in vivo

Abstract

The mitochondrial transcription termination factor proteins are nuclear-encoded nucleic acid binders defined by degenerate tandem helical-repeats of ∼30 amino acids. They are found in metazoans and plants where they localize in organelles. In higher plants, the mTERF family comprises ∼30 members and several of these have been linked to plant development and response to abiotic stress. However, knowledge of the molecular basis underlying these physiological effects is scarce. We show that the Arabidopsis mTERF9 protein promotes the accumulation of the 16S and 23S rRNAs in chloroplasts, and interacts predominantly with the 16S rRNA in vivo and in vitro. Furthermore, mTERF9 is found in large complexes containing ribosomes and polysomes in chloroplasts. The comprehensive analysis of mTERF9 in vivo protein interactome identified many subunits of the 70S ribosome whose assembly is compromised in the null mterf9 mutant, putative ribosome biogenesis factors and CPN60 chaperonins. Protein interaction assays in yeast revealed that mTERF9 directly interact with these proteins. Our data demonstrate that mTERF9 integrates protein-protein and protein-RNA interactions to promote chloroplast ribosomal assembly and translation. Besides extending our knowledge of mTERF functional repertoire in plants, these findings provide an important insight into the chloroplast ribosome biogenesis.

The core autophagy machinery is not required for chloroplast singlet oxygen-mediated cell death in the Arabidopsis thaliana plastid ferrochelatase two mutant

“…Three fts mutants have been shown to affect PENTATRICOPEPTIDE-REPEAT-CONTAINING PROTEIN 30 ( PPR30 ) and “ mitochondrial ” TRANSCRIPTION TERMINATION FACTOR 9 ( mTERF9 ) [ 16 ]. Both genes encode chloroplast-localized proteins predicted to be involved in post-transcriptional gene regulation; PPR30 belongs to the P-class of PPR proteins that regulate gene expression by directly affecting RNA transcript stability, processing, editing, and/or translation [ 21 ] and mTERF9 has been demonstrated to be required for assembly of the 30S ribosome subunit in chloroplasts [ 22 ]. As such, these results suggest a (currently unidentified) chloroplast genome-encoded factor(s) may be required to initiate the 1 O 2 signal.…”

YbeY, éminence grise of ribosome biogenesis

“…In line with the recurrent translational phenotypes, YbeY was found to interact with ribosomal components in bacteria [33,34,53], chloroplasts [54], and mitochondria [3,4], indicating that this association is deeply conserved and mechanistically important. The privileged contact site appears to be the protein uS11 residing in the SSU platform.…”

“…While YbeY does not interact stably with mature ribosomes [3,4,14,[55][56][57], it seems to recognise and transiently associate with certain SSU biogenesis intermediates [33,54], most prominently those containing the highly conserved assembly GTPase Era. YbeY and Era interact closely in mitochondria and bacteria [3,4,53,58], up to the point that the two proteins may be fused in one polypeptide in certain Firmicutes and Acidobacteria.…”

Research Progress in the Molecular Functions of Plant mTERF Proteins

“…In the former, the protein MDA1/mTERF5 promotes the transcription of chloroplast genes [7,45], whereas mTERF6 and mTERF8 are required for transcription termination in this organelle [33,46,47]. In the latter, BSM/RUG2/mTERF4, mTERF15, Zm-mTERF4, and ZmSmk3 participate in RNA splicing in chloroplasts or mitochondria [6,26,38,48], whereas mTERF9 promotes chloroplast ribosomal assembly and translation [51]. Colors of mTERF proteins and arrows refer to their activity as regulators of (i) transcription (blue), functioning as transcriptional pausing and stabilization (MDA1/mTERF5) or terminator (mTERF6 and mTERF8) factors of chloroplast genes (psbEFLJ polycistron, ndhA gene, and rpoA operon), (ii) group II intron splicing (red) of chloroplast (BSM/RUG2/mTERF4 and Zm-mTERF4) or mitochondria (mTERF15 and ZmSMK3) clpP, trnI, trnA, rpl2, rpl16, rps16, nad1, ndhB, nad1, nad2 and nad4 genes or (iii) translation (orange) of chloroplasts (mTERF9) promoting ribosomal assembly.…”

“…The mTERF9 protein, also known as TWIRT1 [69], is localized to chloroplasts [26,68]. In a very recent work, published this year, Méteignier and collaborators, who already contributed to elucidating the molecular mechanisms of MDA1/mTERF5 function [7], have performed a comprehensive analysis of the molecular function mTERF9 [51]. In this work, these authors find that the loss of function of mTERF9 causes a pleiotropic photosynthetic deficiency by comparing the PS I and PSII activity of the Arabidopsis mterf9 mutant and the WT.…”