Redox activity of thioredoxin z and fructokinase-like protein 1 is dispensable for autotrophic growth of Arabidopsis thaliana

Matthias Wimmelbacher,Frederik Börnke

doi:10.1093/jxb/eru122

Abstract

Redox modulation of protein activity by thioredoxins (TRXs) plays a key role in cellular regulation. Thioredoxin z (TRX z) and its interaction partner fructokinase-like protein 1 (FLN1) represent subunits of the plastid-encoded RNA polymerase (PEP), suggesting a role of both proteins in redox regulation of chloroplast gene expression. Loss of TRX z or FLN1 expression generates a PEP-deficient phenotype and renders the plants incapable to grow autotrophically. This study shows that PEP function in trx z and fln1 plants can be restored by complementation with redox-inactive TRX z C106S and FLN1 C105/106A protein variants, respectively. The complemented plants showed wild-type levels of chloroplast gene expression and were restored in photosynthetic capacity, indicating that redox regulation of PEP through TRX z/FLN1 per se is not essential for autotrophic growth. Promoter–reporter gene studies indicate that TRX z and FLN1 are expressed during early phases of leaf development while expression ceases at maturation. Taken together, our data support a model in which TRX z and FLN1 are essential structural components of the PEP complex and their redox activity might only play a role in the fine tuning of PEP function.

Highlights

Due to their sessile life style, plants have evolved a multitude of regulatory mechanisms that enable them to maintain their cellular homeostasis under constantly fluctuating environmental conditions
This study shows that plastid-encoded RNA polymerase (PEP) function in trx z and fln1 plants can be restored by complementation with redox-inactive Thioredoxin z (TRX z) C106S and fructokinase-like protein 1 (FLN1) C105/106A protein variants, respectively
A C106S mutation abolishes the interaction of TRX z with FLN1 and FLN2 while a C109S substitution has no effect on the interaction (Arsova et al, 2010)

Summary

Introduction

Due to their sessile life style, plants have evolved a multitude of regulatory mechanisms that enable them to maintain their cellular homeostasis under constantly fluctuating environmental conditions. Redox modification of proteins is one route through which redox signals can be translated into cellular responses. Depending on their oxidation state, cysteine residues within proteins can form inter- or intramolecular disulphide bonds which can profoundly influence protein conformation and activity. Redox modifications of cysteine residues are controlled by small disulphide oxidoreductases named thioredoxins (TRXs) and glutaredoxins (Schürmann and Buchanan, 2008; Meyer et al, 2009; König et al, 2012). TRXs are encoded by a gene family that is expanded in higher plants. The Arabidopsis thaliana genome codes for more than 20 typical TRX genes and about 30 TRXlike proteins (Meyer et al, 2007, 2012). The complexity is high in plastids, which contain 10 TRX isoforms

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