Evidence for a Role of Chloroplastic m-Type Thioredoxins in the Biogenesis of Photosystem II in Arabidopsis

Abstract

Chloroplastic m-type thioredoxins (TRX m) are essential redox regulators in the light regulation of photosynthetic metabolism. However, recent genetic studies have revealed novel functions for TRX m in meristem development, chloroplast morphology, cyclic electron flow, and tetrapyrrole synthesis. The focus of this study is on the putative role of TRX m1, TRX m2, and TRX m4 in the biogenesis of the photosynthetic apparatus in Arabidopsis (Arabidopsis thaliana). To that end, we investigated the impact of single, double, and triple TRX m deficiency on chloroplast development and the accumulation of thylakoid protein complexes. Intriguingly, only inactivation of three TRX m genes led to pale-green leaves and specifically reduced stability of the photosystem II (PSII) complex, implying functional redundancy between three TRX m isoforms. In addition, plants silenced for three TRX m genes displayed elevated levels of reactive oxygen species, which in turn interrupted the transcription of photosynthesis-related nuclear genes but not the expression of chloroplast-encoded PSII core proteins. To dissect the function of TRX m in PSII biogenesis, we showed that TRX m1, TRX m2, and TRX m4 interact physically with minor PSII assembly intermediates as well as with PSII core subunits D1, D2, and CP47. Furthermore, silencing three TRX m genes disrupted the redox status of intermolecular disulfide bonds in PSII core proteins, most notably resulting in elevated accumulation of oxidized CP47 oligomers. Taken together, our results suggest an important role for TRX m1, TRX m2, and TRX m4 proteins in the biogenesis of PSII, and they appear to assist the assembly of CP47 into PSII.

Two distinct redox cascades cooperatively regulate chloroplast functions and sustain plant viability

“…What is the significance of chloroplast redox regulation in vivo? To address this question, a number of studies using FTR (48,49), Trx (24,35,(50)(51)(52)(53), or NTRC (15,16,27,54) mutant plants have been reported even during the last few years. Most of these studies focused on the in vivo function of individual redox-mediator proteins.…”

Thioredoxin and NADPH-Dependent Thioredoxin Reductase C Regulation of Tetrapyrrole Biosynthesis

“…In contrast, oxidized proteins with disulfide bridges or bound sulfenic acids cannot bind AMS. AMS-labeled proteins migrate more slowly on nonreducing SDS-PAGE gels than unlabeled proteins (Kobayashi et al, 1997;Ikegami et al, 2007;Karamoko et al, 2011;Wang et al, 2013). CHLM has three Cys residues (Cys-111, Cys-115, and Cys-177).…”

“…Using tobacco rattle virus-based virus-induced gene silencing (VIGS), we generated Arabidopsis seedlings with inactivated TRX ms expression (Wang et al, 2013) to examine the physiological impact of TRX ms deficiency on Chl biosynthesis. Due to the functional redundancy of the three TRX m genes, only triple TRX m-silencing plants showed a pale-green phenotype compared with the VIGS-GFP(Col-0) control plants (Fig.…”

“…However, Arabidopsis mutants with a deficiency of TRX f and pea (Pisum sativum) plants with TRX f gene silencing did not exhibit macroscopic changes in leaf pigmentation, whereas a palegreen phenotype was observed when both the TRX f and TRX m genes were silenced simultaneously (Luo et al, 2012). Interestingly, we previously found that Arabidopsis plants with virus-induced TRX m1, TRX m2, and TRX m4 silencing (VIGS-TRX m2m4/m1) had pale-green leaves and a strongly reduced Chl content compared with control plants (Wang et al, 2013). This observation led to the suggestion that these TRX m variants play an important role in the Arabidopsis TBS pathway.…”

“…Functional genetic analyses have shown that TRX m4 knockout mutants were affected in cyclic electron flow around PSI (Courteille et al, 2013), while a TRX m3 knockout mutant was affected in meristem development (BenitezAlfonso et al, 2009). Arabidopsis (Arabidopsis thaliana) lines with combined silencing of TRX m1, m2, and m4 were defective in the biogenesis of PSII (Wang et al, 2013). A recent study suggested that TRX m plays a more important role than TRX f in the activation of Fru-1,6-bisphosphatase (FBPase) and sedoheptulose-1,7-bisphosphatase during carbon assimilation (Okegawa and Motohashi, 2015).…”