Functional characterization of chloroplast-targeted RbgA GTPase in higher plants
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Plant RbgA GTPase is targeted to chloroplasts and co-fractionated with chloroplast ribosomes, and plays a role in chloroplast rRNA processing and/or ribosome biogenesis.
Ribosome Biogenesis GTPase A (RbgA) homologs are evolutionarily conserved GTPases that are widely distributed in both prokaryotes and eukaryotes. In this study, we investigated functions of chloroplast-targeted RbgA. Nicotiana benthamiana RbgA (NbRbgA) and Arabidopsis thaliana RbgA (AtRbgA) contained a conserved GTP-binding domain and a plant-specific C-terminal domain. NbRbgA and AtRbgA were mainly localized in chloroplasts, and possessed GTPase activity. Since Arabidopsis rbgA null mutants exhibited an embryonic lethal phenotype, virus-induced gene silencing (VIGS) of NbRbgA was performed in N. benthamiana. NbRbgA VIGS resulted in a leaf-yellowing phenotype caused by disrupted chloroplast development. NbRbgA was mainly co-fractionated with 50S/70S ribosomes and interacted with the chloroplast ribosomal proteins cpRPL6 and cpRPL35. NbRbgA deficiency lowered the levels of mature 23S and 16S rRNAs in chloroplasts and caused processing defects. Sucrose density gradient sedimentation revealed that NbRbgA-deficient chloroplasts contained reduced levels of mature 23S and 16S rRNAs and diverse plastid-encoded mRNAs in the polysomal fractions, suggesting decreased protein translation activity in the chloroplasts. Interestingly, NbRbgA protein was highly unstable under high light stress, suggesting its possible involvement in the control of chloroplast ribosome biogenesis under environmental stresses. Collectively, these results suggest a role for RbgA GTPase in chloroplast rRNA processing/ribosome biogenesis, affecting chloroplast protein translation in higher plants.
KeywordsChloroplast abnormality Nicotiana benthamiana Ribosomal RNA processing Ribosome association Virus-induced gene silencing
This research was supported by the Cooperative Research Program for Agriculture Science & Technology Development [Project Numbers PJ01118901 (Systems & Synthetic Agrobiotech Center) and PJ01114701 (Plant Molecular Breeding Center)] from the Rural Development Administration (to H.-S. Pai), and the Basic Science Research Program (Project Number 2016-11-1224) from the National Research Foundation of Republic of Korea (to Y. Jeon).
Y.J. performed all of the experiments with the help of H.-K.A and Y.W.K. Y.J. and H.-S.P. designed the experiments, discussed the results, and wrote the manuscript.
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Conflict of interest
The authors declare that they have no conflict of interest.
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