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OsNOA1/RIF1 is a functional homolog of AtNOA1/RIF1: implication for a highly conserved plant cGTPase essential for chloroplast function

Hongjia Liu, Edward Lau, Maggie P. Y. Lam, Hung Chu, Sujuan Li, Guo Huang, Peng Guo, Junqi Wang, Liwen Jiang, Ivan K. Chu, Clive Lo and Yuezhi Tao
The New Phytologist
Vol. 187, No. 1 (July 2010), pp. 83-105
Published by: Wiley on behalf of the New Phytologist Trust
Stable URL: http://www.jstor.org/stable/40661494
Page Count: 23
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OsNOA1/RIF1 is a functional homolog of AtNOA1/RIF1: implication for a highly conserved plant cGTPase essential for chloroplast function
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Abstract

The bacterial protein YqeH is a circularly permuted GTPase with homologs encoded by plant nuclear genomes. The rice homolog OsNOA1/RIF1 is encoded by the single-copy gene Os02g01440. OsNOA1/RIF1 is expressed in different tissues and is light-inducible. The OsNOA1/RIF1-EYFP fusion protein was targeted to chloroplasts in transgenic Arabidopsis plants. In addition, the rice homolog was able to rescue most of the growth phenotypes in an Arabidopsis rif1 mutant. Rice (Oryza sativa) OsNOA1/RIF1 RNAi mutant seedlings were chlorotic with reduced pigment contents and lower photosystem II (PSII) efficiency. However, the expressions of the chloroplast-encoded genes rbcL, atpB, psaA and psbA were not affected. By contrast, reduced abundance of the chloroplast 16S rRNA was observed in the mutant. Quantitative ¡TRAQ-LC-MS/MS proteomics investigations revealed proteome changes in the rice mutant consistent with the expected functional role of OsNOA1/RIF1 in chloroplast translation. The RNAi mutant showed significantly decreased expression levels of chloroplast-encoded proteins as well as nuclearencoded components of chloroplast enzyme complexes. Conversely, upregulation of some classes of nonchloroplastic proteins, such as glycolytic and phenylpropanoid pathway enzymes, was detected. Our work provides independent indications that a highly conserved nuclearencoded cGTPase of likely prokaryotic origin is essential for proper chloroplast ribosome assembly and/or translation in plants.

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