Overexpression of TaSIM provides increased drought stress tolerance in transgenic Arabidopsis

https://doi.org/10.1016/j.bbrc.2019.03.007Get rights and content

Highlights

  • TaSIM is expressed in the stamens, pistils, roots, stems and leaves of wheat.

  • ABRE and CRT/DRE cis-acting elements are present in the TaSIM promoter, which is induced by stress, PEG and ABA.

  • Transgenic Arabidopsis overexpressing TaSIM has a low water loss rate, accumulates relatively high contents of soluble sugars and proline, and expresses RD22 and RD29A, thereby enhancing Arabidopsis tolerance to drought stress.

Abstract

Drought is the most serious meteorological disaster affecting wheat production. Members of the R2R3-MYB gene subfamily play a crucial role in the regulation of the wheat drought stress response. In this study, the function of polyethylene glycol (PEG)-induced expression of the wheat R2R3-MYB gene TaSIM in response to drought stress was characterized. β-Glucuronidase (GUS) histochemical staining revealed that the TaSIM promoter can drive the expression of the GUS gene in the flowers, roots, stems and rosette leaves. Moreover, TaSIM was expressed in the stamens, pistils, roots, stems and leaves of wheat. The TaSIM promoter contains a known stress-responsive cis-acting element and is inducible by stress, PEG and abscisic acid (ABA). Under drought stress, compared with wild-type (WT) Arabidopsis, transgenic Arabidopsis overexpressing TaSIM presented significantly lower leaf water loss rates and increased survival. Moreover, the content of soluble sugars and proline and the expression of stress-related genes (RD29A and RD22) in transgenic Arabidopsis overexpressing TaSIM were higher than those in WT Arabidopsis under drought stress. Our results indicate that TaSIM plays a positive role in the drought stress response and can be used as a candidate gene for the genetic engineering of wheat drought resistance.

Introduction

Drought has become a worldwide problem that severely hinders agricultural production. In arid and semiarid regions, drought caused by water deficit is the main environmental factor that restricts plant growth [1]. Plants can sense drought stress and respond to avoid harm. Drought can induce changes by affecting three different interactions in plants: altering gene expression (upregulation, downregulation, coexpression); altering protein synthesis, transport and degradation; and altering metabolic pathways, leading to changes in metabolites. These changes comprehensively regulate plant resistance to drought stress [2]. Transcription factors regulate functional gene expression and signal transduction. To date, hundreds of transcription factors have been isolated from various higher plant species. The expression of many genes related to drought stress is regulated by a few transcription factors. Overexpression of these transcription factor genes (DREB, NAC, bZIP, WRKY, NF-Y and MYB) can improve the ability of plants to adapt to drought stress [2].

MYB proteins are among the most numerous members of plant transcription factors [3]. According to differences of the MYB domain repetition number, MYB proteins can be divided into four categories: MYB1R, R2R3-MYB, R1R2R3-MYB and 4RMYB [3]. At present, research on MYB family genes involved in abiotic stress is still concentrated mainly on the R2R3-MYB subfamily, including OsMYB4, OsMYB48-1 OsMYB55, AtMYB2, AtMYB15, AtMYB41, AtMYB44, AtMYB61 and AtMYB96 [2]. However, members of the MYB1R and R1R2R3-MYB subfamilies have also been shown to be involved in abiotic stress responses. Two MYB1R transcription factors, potato StMYB1R-1 [4] and rice MYBS3 [5], are positive regulators of drought stress and cold stress, respectively. OsMYB3R-2, a rice R1R2R3-MYB gene, is involved in the response to salt, freezing, and drought stress [6]. These studies suggest that members of the MYB1R, R2R3-MYB and R1R2R3-MYB subfamilies of MYB transcription factors may be involved in the response to abiotic stress.

With the largest area and the second largest total output, wheat is the largest food crop worldwide [2]. Common wheat (Triticum aestivum L.) is the most widely grown species, accounting for more than 90% of the total wheat area worldwide, and drought is the most important abiotic stress factor affecting wheat production [1]. Previous studies have identified several MYB transcription factors involved in the wheat drought stress response. For example, under polyethylene glycol (PEG) stress, the expression of 11 wheat MYB genes was downregulated, whereas that of 5 MYB genes was upregulated [7]. Overexpression of TaMYB30-B increases the tolerance of transgenic Arabidopsis to drought stress by upregulating the stress response genes RD29A and ERD1 and increasing the content of proline and soluble sugars, which reduces the malondialdehyde (MDA) content [8]. Likewise, TaMYBsm1-D can also enhance Arabidopsis drought resistance by activating stress response genes and altering physiological indicators of stress [9]. Overexpression of TaMYB31 enhances the drought tolerance of transgenic Arabidopsis by upregulating the expression of stress response genes and wax biosynthesis genes [10]. Transgenic Arabidopsis plants overexpressing TaMYB33 exhibit a strong ability to detoxify reactive oxygen species (ROS) and to regain osmotic balance, thus improving salt and drought tolerance [11]. Similarly, overexpression of TaODORANT1 increases the tolerance to salt and drought stress in transgenic tobacco [12]. Transgenic tobacco overexpressing TaMyb1D exhibits increased resistance to oxidative and drought stress [13]. Moreover, TaPIMP1 positively regulates the response to drought stress in wheat [14] and increases the resistance of transgenic tobacco to drought, oxidative and salt stress [15]. TaMYB2A [16] and TaMYB19 [17] are positive regulators of drought, salt and low temperature stress. However, at least 84 MYB genes are present in wheat [10], but the biological functions of many MYB genes remain unclear. Their role in the drought stress response superficially needs to be further studied.

In our previous studies, we reported that PEG induced TaSIM gene expression [18], but the function of this gene in the drought stress response has not been elucidated. In this study, the expression patterns of TaSIM in different tissues of wheat were characterized. By the use of transformed Arabidopsis, the promoter of TaSIM was cloned and found to be induced by stress, PEG and abscisic acid (ABA). Overexpression of TaSIM improved the tolerance of transgenic Arabidopsis to drought stress by increasing the expression of stress response genes and the level of osmotic adjustment substances. Our results indicate that TaSIM can be used as a candidate gene for the genetic engineering of wheat drought resistance.

Section snippets

Plant materials

In this study, Xinchun 6, the main spring wheat variety planted in Xinjiang, was used as the experimental material. Wheat seedlings were cultured in water at 20 °C for 3 weeks. The roots, stems, and leaves of 3-week-old seedlings as well as pistils and stamens from mature plants grown in the field were harvested separately for subsequent experiments.

Cloning and analysis of cis-acting elements of the TaSIM promoter

Wheat leaf genomic DNA was extracted according to the procedure of an efficient plant genomic DNA extraction kit (Tiangen, Beijing, China). A

Expression pattern of TaSIM in different tissues

To analyze the expression pattern of TaSIM in different tissues, the CaMV35S promoter in pCAMBIA3301 was replaced with a 3000 bp promoter upstream of TaSIM, and the vector was transformed into Arabidopsis. GUS staining analysis of homozygous T3 transgenic Arabidopsis was then performed. The GUS histochemical staining was visible in the flowers, roots, stems and rosette leaves of pTaSIM:GUS transgenic Arabidopsis plants (Fig. 1A), indicating that the TaSIM promoter can drive the expression of

Discussion

ABA is a broad-spectrum phytohormone that not only regulates stomatal opening, growth and development but also coordinates various stress signal transduction pathways [20]. Transcription factors can be divided into two categories on the basis of their ABA signaling pathways during plant stress tolerance: ABA-dependent and ABA-independent pathways [21]. Studies have shown that wheat MYB transcription factors participate in not only the stress response of ABA-dependent pathways but also the

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Funding

This work was supported by the National Natural Science Foundation of China (31360264, 31660295 and 31860295).

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