Plastidial Thioredoxin z Interacts with Two Fructokinase-Like Proteins in a Thiol-Dependent Manner: Evidence for an Essential Role in Chloroplast Development in Arabidopsis and Nicotiana benthamiana    

Abstract

Here, we characterize a plastidial thioredoxin (TRX) isoform from Arabidopsis thaliana that defines a previously unknown branch of plastidial TRXs lying between x-and y-type TRXs and thus was named TRX z. An Arabidopsis knockout mutant of TRX z had a severe albino phenotype and was inhibited in chloroplast development. Quantitative real-time RT-PCR analysis of the mutant suggested that the expressions of genes that depend on a plastid-encoded RNA polymerase (PEP) were specifically decreased. Similar results were obtained upon virus-induced gene silencing (VIGS) of the TRX z ortholog in Nicotiana benthamiana. We found that two fructokinase-like proteins (FLN1 and FLN2), members of the pfkB-carbohydrate kinase family, were potential TRX z target proteins and identified conserved Cys residues mediating the FLN-TRX z interaction. VIGS in N. benthamiana and inducible RNA interference in Arabidopsis of FLNs also led to a repression of PEPdependent gene transcription. Remarkably, recombinant FLNs displayed no detectable sugar-phosphorylating activity, and amino acid substitutions within the predicted active site imply that the FLNs have acquired a new function, which might be regulatory rather than metabolic. We were able to show that the FLN2 redox state changes in vivo during light/dark transitions and that this change is mediated by TRX z. Taken together, our data strongly suggest an important role for TRX z and both FLNs in the regulation of PEP-dependent transcription in chloroplasts.

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

“…S9) (42, 43). Arsova et al demonstrated that Trx-z binds to two fructokinase-like proteins (FLNs) in a thiol-dependent manner, which is essential for plastid-encoded RNA polymerase (PEP)-dependent gene expression and proper chloroplast development (42). In accordance with this report, Trx-z and FLNs were identified as PEP complex components by proteomic studies (44,45).…”

The ROXY1 C-Terminal L**LL Motif Is Essential for the Interaction with TGA Transcription Factors

“…The CC-type class expanded exclusively and strongly during the evolution of land plants, suggesting that this class of GRXs might have been recruited to participate in the evolution of more complex land plants (Xing et al, 2006;Ziemann et al, 2009). Contrasting with wide-ranging roles of plant thioredoxins in chloroplast and mitochondrial processes, seed development and germination, and auxin signaling (Buchanan and Balmer, 2005;Reichheld et al, 2007;Arsova et al, 2010;Bashandy et al, 2010), the biological and physiological functions of plant GRXs have remained largely elusive. Recently, two CC-type GRX genes, ROXY1 and ROXY2, were functionally characterized, revealing their functions during Arabidopsis flower development Xing and Zachgo, 2008;).…”

A Functional Component of the Transcriptionally Active Chromosome Complex, Arabidopsis pTAC14, Interacts with pTAC12/HEMERA and Regulates Plastid Gene Expression

“…1C). This distinct location of pTAC14 is reminiscent of reports of thylakoid-associated proteins, including MPF1 (Jeong et al, 2003), PEND (Terasawa and Sato, 2009), sulfite reductase (Sekine et al, 2007), CND41 (Murakami et al, 2000), and other characterized TAC components, such as FSD3 , FLN1, and FLN2 (Arsova et al, 2010). These proteins were suggested to be tightly associated with plastid nucleoids.…”

“…pTAC14 Regulates PEP Activity in Chloroplast like those that are detected in other TAC mutants, such as ptac6 and ptac12 (Pfalz et al, 2006), atmurE (Garcia et al, 2008), trxz (Arsova et al, 2010), fln1 (Arsova et al, 2010), and fsd2 and fsd3 . Similarly, differently sized vesicles can be observed in the chloroplasts of these mutants.…”

“…They named 18 components, which were not studied in depth at that time, as pTACs (for plastid TAC proteins). Among the recent advances made in the study of TACs, several components responsible for the albino or pale-green phenotype have been described, such as heteromeric FSD2 and FSD3 , Whirly proteins (Maréchal et al, 2009), pTAC4/Vipp1 (Kroll et al, 2001;Aseeva et al, 2007), pTAC2/6/12 (Pfalz et al, 2006), AtMurE (Garcia et al, 2008), TRXz (Arsova et al, 2010), and FLN1 and FLN2 (Arsova et al, 2010). Recently, Chen et al (2010) found that HEMERA, previously called pTAC12, had a function in the nucleus, where it acted specifically in phytochrome signaling.…”