NADPH-Thioredoxin Reductase C Mediates the Response to Oxidative Stress and Thermotolerance in the Cyanobacterium Anabaena sp. PCC7120.

Ana M Sánchez-Riego,Francisco J Florencio,Carla V Galmozzi,Alejandro Mata-Cabana

doi:10.3389/fmicb.2016.01283

Abstract

NADPH-thioredoxin reductase C (NTRC) is a bimodular enzyme composed of an NADPH-thioredoxin reductase and a thiioredoxin domain extension in the same protein. In plants, NTRC has been described to be involved in the protection of the chloroplast against oxidative stress damage through reduction of the 2-Cys peroxiredoxin (2-Cys Prx) as well as through other functions related to redox enzyme regulation. In cyanobacteria, the Anabaena NTRC has been characterized in vitro, however, nothing was known about its in vivo function. In order to study that, we have generated the first knockout mutant strain (ΔntrC), apart from the previously described in Arabidopsis. Detailed characterization of this strain reveals a differential sensitivity to oxidative stress treatments with respect to the wild-type Anabaena strain, including a higher level of ROS (reactive oxygen species) in normal growth conditions. In the mutant strain, different oxidative stress treatments such as hydrogen peroxide, methyl-viologen or high light irradiance provoke an increase in the expression of genes related to ROS detoxification, including AnNTRC and peroxiredoxin genes, with a concomitant increase in the amount of AnNTRC and 2-Cys Prx. Moreover, the role of AnNTRC in the antioxidant response is confirmed by the observation of a pronounced overoxidation of the 2-Cys Prx and a time-delay recovery of the reduced form of this protein upon oxidative stress treatments. Our results suggest the participation of this enzyme in the peroxide detoxification in Anabaena. In addition, we describe the role of Anabaena NTRC in thermotolerance, by the appearance of high molecular mass AnNTRC complexes, showing that the mutant strain is more sensitive to high temperature treatments.

Highlights

Cyanobacteria and chloroplasts possess redox systems that allow them to link the photosynthetic electron transport process with metabolism regulation through disulphide-mediated thiolbased redox mechanisms
The thioredoxin reduction function in cyanobacteria is performed by the Ferredoxin-thioredoxin reductase (FTR) and the NADPH-thioredoxin Reductase (NTR), receiving the reducing equivalents from the photosynthetic electron transport and the NADPH, respectively
The genome analysis of the cyanobacteria phylum revealed that, despite being photosynthetic organisms, not all species have genes coding for FTR, but all the analyzed ones have at least one for NTR (Florencio et al, 2006; Balsera et al, 2014)

Summary

Introduction

Cyanobacteria and chloroplasts possess redox systems that allow them to link the photosynthetic electron transport process with metabolism regulation through disulphide-mediated thiolbased redox mechanisms These systems are important to cope with ROS generation derived from molecular oxygen production (Lindahl et al, 2011; Balsera et al, 2014). To what was described for Mycobacterium leprae (Wieles et al, 1995), a new type of NTR fused to a Trx domain was identified in the chloroplast of rice and Arabidopsis thaliana (Serrato et al, 2004) This new NTR was named NADPH-thioredoxin reductase C (NTRC). Heat shock-regulated chaperone activity has been demonstrated for the Arabidopsis NTRC (Chae et al, 2013) in which a switch in the oligomerization state of the protein occurs from low to high molecular mass complexes

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Conclusion