The CsHSP17.2 molecular chaperone is essential for thermotolerance in Camellia sinensis

Mingle Wang,Xuan Chen,Zhongwei Zou,Kang Sun,Qinghui Li,Xinghui Li

doi:10.1038/s41598-017-01407-x

Mingle Wang, Xuan Chen + Show 4 more

Open Access

https://doi.org/10.1038/s41598-017-01407-x

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Abstract

Small heat shock proteins (sHSPs) play important roles in responses to heat stress. However, the functions of sHSPs in tea plants (Camellia sinensis) remain uncharacterized. A novel sHSP gene, designated CsHSP17.2, was isolated from tea plants. Subcellular localization analyses indicated that the CsHSP17.2 protein was present in the cytosol and the nucleus. CsHSP17.2 expression was significantly up-regulated by heat stress but was unaffected by low temperature. The CsHSP17.2 transcript levels increased following salt and polyethylene glycol 6000 treatments but decreased in the presence of abscisic acid. The molecular chaperone activity of CsHSP17.2 was demonstrated in vitro. Transgenic Escherichia coli and Pichia pastoris expressing CsHSP17.2 exhibited enhanced thermotolerance. The transgenic Arabidopsis thaliana exhibited higher maximum photochemical efficiencies, greater soluble protein proline contents, higher germination rates and higher hypocotyl elongation length than the wild-type controls. The expression levels of several HS-responsive genes increased in transgenic A. thaliana plants. Additionally, the CsHSP17.2 promoter is highly responsive to high-temperature stress in A. thaliana. Our results suggest that CsHSP17.2 may act as a molecular chaperone to mediate heat tolerance by maintaining maximum photochemical efficiency and protein synthesis, enhancing the scavenging of reactive oxygen species and inducing the expression of HS-responsive genes.

Highlights

Heat shock (HS) is induced by a higher temperature, which is approximately 10–15 °C above the optimal growth temperature[1, 2]
Sequence alignments with the deduced CsHSP17.2 protein sequence and those of other plant small HSPs (sHSPs) indicated that CsHSP17.2 contains a conserved 90-amino-acid C-terminal α-crystallin domain[5], which can be further divided into two homologous regions, namely, consensus region I and consensus region II (Fig. S1a)
Since the first sHSP was discovered in Drosophila melanogaster, numerous sHSPs have been identified in various plant species[5, 30]

Summary

Introduction

Heat shock (HS) is induced by a higher temperature, which is approximately 10–15 °C above the optimal growth temperature[1, 2]. In addition to HS, the expression of sHSP genes can be induced by other abiotic stress, including salinity[12], low temperature[13] and drought[14]. Overexpression of AsHSP17, a new sHSP gene from creeping bentgrass (Agrostis stolonifera), negatively regulate plant responses to adverse environmental stresses in transgenic A. thaliana[22]. High-temperatures are likely the most important abiotic stress for tea plants because they can considerably affect crop quality and yield. Pre-experimental results revealed that CsHSP17.2 (GenBank accession number: KU244518) was more highly expressed following exposure to HS than the other HS-inducible genes. These results suggested that CsHSP17.2 affected heat tolerance in C. sinensis. The results of this study may lead to a more thorough characterization of the molecular basis of thermotolerance in C. sinensis

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