The significance of cysteine synthesis for acclimation to high light conditions.

Anna Speiser,Karl-Josef Dietz,Mutsumi Watanabe,Markus Wirtz,RÃ¼diger Hell,Kazuki Saito,Stefan Haberland

doi:10.3389/fpls.2014.00776

Abstract

Situations of excess light intensity are known to result in the emergence of reactive oxygen species that originate from the electron transport chain in chloroplasts. The redox state of glutathione and its biosynthesis contribute importantly to the plant's response to this stress. In this study we analyzed the significance of cysteine synthesis for long-term acclimation to high light conditions in Arabidopsis thaliana. Emphasis was put on the rate-limiting step of cysteine synthesis, the formation of the precursor O-acetylserine (OAS) that is catalyzed by serine acetyltransferase (SERAT). Wild type Arabidopsis plants responded to the high light condition (800 μmol m−2 s−1 for 10 days) with synthesis of photo-protective anthocyanins, induction of total SERAT activity and elevated glutathione levels when compared to the control condition (100 μmol m−2 s−1). The role of cysteine synthesis in chloroplasts was probed in mutant plants lacking the chloroplast isoform SERAT2;1 (serat2;1) and two knock-out alleles of CYP20-3, a positive interactor of SERAT in the chloroplast. Acclimation to high light resulted in a smaller growth enhancement than wild type in the serat2;1 and cyp20-3 mutants, less induction of total SERAT activity and OAS levels but similar cysteine and glutathione concentrations. Expression analysis revealed no increase in mRNA of the chloroplast SERAT2;1 encoding SERAT2;1 gene but up to 4.4-fold elevated SERAT2;2 mRNA levels for the mitochondrial SERAT isoform. Thus, lack of chloroplast SERAT2;1 activity or its activation by CYP20-3 prevents the full growth response to high light conditions, but the enhanced demand for glutathione is likely mediated by synthesis of OAS in the mitochondria. In conclusion, cysteine synthesis in the chloroplast is important for performance but is dispensable for survival under long-term exposure to high light and can be partially complemented by cysteine synthesis in mitochondria.

Highlights

Reactive oxygen species (ROS) play a dual role in plants since they function as regulators and if excessively produced as harmful reactive metabolites
Wild type Arabidopsis plants responded to the high light condition (800 μmol m−2 s−1 for 10 days) with synthesis of photo-protective anthocyanins, induction of total serine acetyltransferase (SERAT) activity and elevated glutathione levels when compared to the control condition (100 μmol m−2 s−1)
In this study we investigated whether cysteine synthesis in the chloroplast has a specific role for high light acclimation in Arabidopsis, since it provides the thiol-harboring building block for glutathione

Summary

Introduction

Reactive oxygen species (ROS) play a dual role in plants since they function as regulators and if excessively produced as harmful reactive metabolites. The effects on growth of high light and the associated excess excitation energy in chloroplasts have been discussed in literature extensively (Foyer et al, 2009; Suzuki et al, 2012; Szechynska-Hebda and Karpinski, 2013). Among these responses are morphological changes of the leaves (Eckardt et al, 1997), accumulation of anthocyanins as scavengers of evolving ROS (Chalker-Scott, 1999; Gould et al, 2002; Vanderauwera et al, 2005; Zeng et al, 2010) and the expression of high light-induced genes (Alsharafa et al, 2014). A well-characterized excess light-induced gene is APX2 that encodes for ascorbate-peroxidase 2, as part of the ascorbate-glutathione ROS detoxification cycle (Rossel et al, 2006; Foyer and Noctor, 2011; Noctor et al, 2011)

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Conclusion