The walnut transcription factor JrGRAS2 contributes to high temperature stress tolerance involving in Dof transcriptional regulation and HSP protein expression

Kaiheng Ma,Guiyan Yang,Xiangqian Gao,Caixia Jia,Dapei Li,Zhenggang Xu,Meizhi Zhai

doi:10.1186/s12870-018-1568-y

Abstract

BackgroundGRAS transcription factor (TF) family is unique and numerous in higher plants with diverse functions that involving in plant growth and development processes, such as gibberellin (GA) signal transduction, root development, root nodule formation, and mycorrhiza formation. Walnut tree is exposed to various environmental stimulus that causing concern about its resistance mechanism. In order to understand the molecular mechanism of walnut to adversity response, a GRAS TF (JrGRAS2) was cloned and characterized from Juglans regia in this study.ResultsA 1500 bp promoter fragment of JrGRAS2 was identified from the genome of J. regia, in which the cis-elements were screened. This JrGRAS2 promoter displayed expression activity that was enhanced significantly by high temperature (HT) stress. Yeast one-hybrid assay, transient expression and chromatin immunoprecipitation (Chip)-PCR analysis revealed that JrDof3 could specifically bind to the DOFCOREZM motif and share similar expression patterns with JrGRAS2 under HT stress. The transcription of JrGRAS2 was induced by HT stress and up-regulated to 6.73-~11.96-fold in the leaf and 2.53-~4.50-fold in the root to control, respectively. JrGRAS2 was overexpressed in Arabidopsis, three lines with much high expression level of JrGRAS2 (S3, S7, and S8) were selected for HT stress tolerance analysis. Compared to the wild type (WT) Arabidopsis, S3, S7, and S8 exhibited enhanced seed germination rate, fresh weight accumulation, and activities of catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and glutathione-S-transferase (GST) under HT stress. In contrast, the Evans blue staining, electrolyte leakage (EL) rates, hydrogen dioxide (H2O2) and malondialdehyde (MDA) content of transgenic seedlings were all lower than those of WT exposed to HT stress. Furthermore, the expression of heat shock proteins (HSPs) in S3, S7, and S8 was significant higher than those in WT plants. The similar results were obtained in JrGRAS2 transient overexpression walnut lines under normal and HT stress conditions.ConclusionsOur results suggested that JrDof3 TF contributes to improve the HT stress response of JrGRAS2, which could effectively control the expression of HSPs to enhance HT stress tolerance. JrGRAS2 is an useful candidate gene for heat response in plant molecular breeding.

Highlights

GRAS transcription factor (TF) family is unique and numerous in higher plants with diverse functions that involving in plant growth and development processes, such as gibberellin (GA) signal transduction, root development, root nodule formation, and mycorrhiza formation
Identification and High temperature (HT) stress response of JrGRAS2 promoter A 1500 bp promoter segment of JrGRAS2 was identified from the J. regia genome that was located in the 874811-870000 (NW_017443591.1) region of the walnut genome [41]
The JrGRAS2 promoter fragment was inserted into pCAMBIA1301 vector and transformed into Arabidopsis and walnut plants, which were further stained to reveal that the promoter caused GUS expression in the leaves and roots

Summary

Introduction

GRAS transcription factor (TF) family is unique and numerous in higher plants with diverse functions that involving in plant growth and development processes, such as gibberellin (GA) signal transduction, root development, root nodule formation, and mycorrhiza formation. Walnut tree is exposed to various environmental stimulus that causing concern about its resistance mechanism. High temperature (HT) stress is one of the most important limiting factors to plant growth and productivity [1]; warming surface temperatures and increasing frequency and duration of widespread droughts threaten the health of natural forests and agricultural crops [2]. A decrease in individual grain weight resulted in significant reduction in rice grain production per unit area [9]. Zhao et al (2017) point out that without effective adaptation, CO2 fertilization, and genetic improvement, each degree-Celsius increase in global mean temperature would, on average, reduce global yields of maize by 7.4%, wheat by 6.0%, rice by 3.2%, and soybean by 3.1% [10]. The damage caused by HT to plants should not be underestimated

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