A nuclear gene of Chlamydomonas reinhardtii, Tba1, encodes a putative oxidoreductase required for translation of the chloroplast psbA mRNA

Abstract

SummaryBiosynthesis of chloroplast proteins is to a large extent regulated post-transcriptionally, and a number of nuclear-encoded genes have been identified that are required for translation or stability of specific chloroplast mRNAs. A nuclear mutant of Chlamydomonas reinhardtii, hf261, deficient in the translation of the psbA mRNA, has reduced association of the psbA mRNA with ribosomes and is deficient in binding of the chloroplast localized poly (A) binding protein (cPAB1) to the psbA mRNA. Cloning of the hf261 locus and complementation of hf261 using a wt genomic clone has identified a novel gene, Tba1, for translational affector of psbA. Strains complemented with the wt Tba1 gene restore the ability of the psbA mRNA to associate with ribosomes, and restores RNA binding activity of cPAB1 for the psbA mRNA. Analysis of the Tba1 gene identified a protein with significant homology to oxidoreductases. The effect of Tba1 expression on the RNA binding activity of cPAB1, and on the association of psbA mRNA with ribosomes, implies that Tba1 functions as a redox regulator of cPAB1 RNA binding activity to indirectly promote psbA mRNA translation initiation. A model of chloroplast translation incorporating Tba1 and other members of the psbA mRNA binding complex is presented.

LOW PSII ACCUMULATION1 Is Involved in Efficient Assembly of Photosystem II inArabidopsis thaliana

“…Several mutants have also been isolated that have specific deficiencies in translation of psbA and psbC mRNA. Tba1 of Chlamydomonas encodes a putative oxidoreductase that functions as a redox regulator of cPAB1 RNA binding activity and, thus, indirectly promotes psbA mRNA translation initiation (Somanchi et al, 2005). The Tbc2 gene product, together with Tbc1 and Tbc3, is required for translation of psbC mRNA in Chlamydomonas (Auchincloss et al, 2002).…”

Expression of Plastid Genes: Organelle-Specific Elaborations on a Prokaryotic Scaffold

“…Light activates the initiation of psbA translation via the psbA 5# UTR (for review, see PeledZehavi and Danon, 2007). Genetic screens identified the Arabidopsis protein HCF173 (Schult et al, 2007) and the Chlamydomonas protein Tba1 (Somanchi et al, 2005) as being required specifically for psbA translation. HCF173 and Tba1 are unrelated, they are not PPR-like proteins, and their mechanisms of action are unknown.…”

The Metabolic Status Drives Acclimation of Iron Deficiency Responses in Chlamydomonas reinhardtii as Revealed by Proteomics Based Hierarchical Clustering and Reverse Genetics

“…The finding of a constant up-regulation of CYN37 under iron deficiency stress or PA conditions underpins this notion. TBA1 encodes a putative oxidoreductase required for translation of the chloroplast psbA mRNA (67). Up-regulation of chloroplast localized TBA1 may reflect high turnover of the D1 protein, thereby requiring increased translation of psbA RNA.…”