Abstract

DnaJ proteins act as essential molecular chaperones in protein homeostasis and protein complex stabilization under stress conditions. The roles of a tomato (Lycopersicon esculentum) chloroplast-targeted DnaJ protein (LeCDJ1), whose expression was upregulated by treatment at 4 and 42 °C, and with high light, NaCl, polyethylene glycol, and H2O2, were investigated here using sense and antisense transgenic tomatoes. The sense plants exhibited not only higher chlorophyll content, fresh weight and net photosynthetic rate, but also lower accumulation of reactive oxygen species and membrane damage under chilling stress. Moreover, the maximal photochemistry efficiency of photosystem II (PSII) (F v/F m) and D1 protein content were higher in the sense plants and lower in the antisense plants, and the photoinhibitory quenching was lower in the sense plants and higher in the antisense plants, suggesting that the inhibition of PSII was less severe in the sense plants and more severe in the antisense plants compared with the wild type. Furthermore, the PSII protein complexes were also more stable in the sense plants. Interestingly, the sense plants treated with streptomycin (SM), an inhibitor of organellar translation, still showed higher F v/F m, D1 protein content and PSII stability than the SM-untreated antisense plants. This finding suggested that the protective effect of LeCDJ1 on PSII was, at least partially, independent of D1 protein synthesis. Furthermore, chloroplast heat-shock protein 70 was identified as the partner of LeCDJ1. These results indicate that LeCDJ1 has essential functions in maintaining PSII under chilling stress.

Highlights

  • Photosystem II (PSII) is a large pigment–protein complex in the thylakoid membrane that performs the key reactions of photosynthesis (Shi et al, 2012)

  • The maximal photochemistry efficiency of photosystem II (PSII) (Fv/Fm) and D1 protein content were higher in the sense plants and lower in the antisense plants, and the photoinhibitory quenching was lower in the sense plants and higher in the antisense plants, suggesting that the inhibition of PSII was less severe in the sense plants and more severe in the antisense plants compared with the wild type

  • The denatured protein complexes were electroblotted onto polyvinylidene fluoride (PVDF) membranes, probed with D1 antibody, LeCDJ1 was isolated from a tomato cDNA library representing the expression patterns of genes affected by chilling

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Summary

Introduction

Photosystem II (PSII) is a large pigment–protein complex in the thylakoid membrane that performs the key reactions of photosynthesis (Shi et al, 2012). It exists mainly in dimeric form with the monomer containing at least 27–28 subunits (Rochaix, 2011). Chilling stress is one of the most significant environmental stresses on agricultural plants. Numerous studies have shown that chilling stress inhibits PSII activity (Li et al, 2010; Duan et al, 2012). Plants exposed to chilling stress show reduced metabolic rates (Partelli et al, 2009)

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