Discovery of a novel repeated RNA-binding motif conserved in diverse uncharacterized proteins of photosynthetic organisms
Final Report Abstract
We aimed at studying the role of HCF145 and other TMR proteins in RNA binding. We demonstrated that HCF145 binds 5 nucleotides downstream of the psaA 5’ end and protects the RNA against 5’-> 3’ exonucleases most likely indirectly by inducing masking of the 5’ end. In vivo association of HCF145 with the psbN and ycf2 RNAs has a minor role as revealed by transplastomic studies in tobacco. Viable mutants of HCF145-L containing a ligand-binding domain closely related to those in HCF145 were generated and are presently transformed with a GFP-tagged version to identify the ligand, which is suspected to be identical or at least closely related to the one of HCF145. We could show that the plastid UMP kinase is not related to the function of HCF145 in the specific stabilization the psaA-psaB-rps14 mRNA as reported before (Hein et al. 2009) but beside its discovered enzymatic function it most likely has a moonlighting function in the regulation of the metabolism of several plastid group II introns. Thus, the plastid transcript pattern in pumpkin is similar to that in mutants generally affected in plastid gene expression, i.e. transcription and/or translation. Our work provides clear evidence for a novel RNA binding family containing multiple repeats with a conserved but partially scattered signature predicted to form a superhelical structure. High quality purification of several representative TMR proteins was achieved for the initiation of crystallographic studies. The cyanobacterial origin of the TMR motif as well as localization studies in P. patens and Arabidopsis imply that TMR proteins are generally located within the chloroplast. TMR proteins tend to form homomultimers and recognize similar target RNAs owing to their conserved signature in contrast to the degenerated code of PPR proteins. Accordingly, TMR mutants of P. patens show an effect on photosynthesis. Three TMR mutants of C. merolae and corresponding localization and functional studies are under investigation.
Publications
- (2015) High Chlorophyll Fluorescence 145 binds to and stabilizes the psaA 5’ UTR via a newly defined repeat motif in Embryophyta. Plant Cell. 27, 2600-261
Manavski N., Torabi S., Lezhneva L., Arif M.A., Frank W. and Meurer J.
(See online at https://doi.org/10.1105/tpc.15.00234) - (2017) Pale Cress binds to plastid RNAs and facilitates the biogenesis of the 50S ribosomal subunit. Plant J. 92, 400-413
Meurer J., Schmid L.M., Stoppel R., Leister D., Brachmann A. and Manavski N.
(See online at https://doi.org/10.1111/tpj.13662) - (2018) RNA-stabilization factors in chloroplasts of vascular plants. Essays Biochem. 62, 51-64
Manavski N., Schmid L.M. and Meurer J.
(See online at https://doi.org/10.1042/EBC20170061) - (2019) PUMPKIN, the sole plastid UMP kinase, associates with group II introns and alters their metabolism. Plant Physiol. 179, 248-264
Schmid L.M., Ohler L., Möhlmann T., Brachmann A., Muiño J.M., Leister D., Meurer J. and Manavski N.
(See online at https://doi.org/10.1104/pp.18.00687)
