Sweetpotato bZIP Transcription Factor IbABF4 Confers Tolerance to Multiple Abiotic Stresses.

Wenbin Wang,Xiaoyun Jia,Sang-Soo Kwak,Yanxin Yang,Ho Soo Kim,Huan Yu,Xiangpo Qiu

doi:10.3389/fpls.2019.00630

Abstract

The abscisic acid (ABA)-responsive element binding factors (ABFs) play important regulatory roles in multiple abiotic stresses responses. However, information on the stress tolerance functions of ABF genes in sweetpotato (Ipomoea batatas [L.] Lam) remains limited. In the present study, we isolated and functionally characterized the sweetpotato IbABF4 gene, which encodes an abiotic stress-inducible basic leucine zipper (bZIP) transcription factor. Sequence analysis showed that the IbABF4 protein contains a typical bZIP domain and five conserved Ser/Thr kinase phosphorylation sites (RXXS/T). The IbABF4 gene was constitutively expressed in leaf, petiole, stem, and root, with the highest expression in storage root body. Expression of IbABF4 was induced by ABA and several environmental stresses including drought, salt, and heat shock. The IbABF4 protein localized to the nucleus, exhibited transcriptional activation activity, and showed binding to the cis-acting ABA-responsive element (ABRE) in vitro. Overexpression of IbABF4 in Arabidopsis thaliana not only increased ABA sensitivity but also enhanced drought and salt stress tolerance. Furthermore, transgenic sweetpotato plants (hereafter referred to as SA plants) overexpressing IbABF4, generated in this study, exhibited increased tolerance to drought, salt, and oxidative stresses on the whole plant level. This phenotype was associated with higher photosynthetic efficiency and lower malondialdehyde and hydrogen peroxide content. Levels of endogenous ABA content and ABA/stress-responsive gene expression were significantly upregulated in transgenic Arabidopsis and sweetpotato plants compared with wild-type plants under drought stress. Our results suggest that the expression of IbABF4 in Arabidopsis and sweetpotato enhances tolerance to multiple abiotic stresses through the ABA signaling pathway.

Highlights

Abiotic stresses such as drought, salinity, and high temperature severely affect plant growth, development, and productivity (Moore et al, 2009)
The relative expression level of IbABF4 in sweetpotato plants exposed to abscisic acid (ABA), polyethylene glycol (PEG), NaCl, and heat was measured by Quantitative Real-Time PCR (qRT-PCR) (Figure 2B)
In plants exposed to 10 μM ABA, the relative expression level of IbABF4 started increasing at 3 h, reaching a peak at 6 h, and declining over the following 12 h

Summary

Introduction

Abiotic stresses such as drought, salinity, and high temperature severely affect plant growth, development, and productivity (Moore et al, 2009). IbABF4 Increases Abiotic Stresses Tolerance involving transcription factors (TFs) that bind to conserved cis-acting elements in target gene promoters, activating their expression and leading to enhanced stress tolerance (Fujita et al, 2005). Numerous stress-responsive TFs, such as those belonging to the basic leucine zipper (bZIP), WRKY, MYB, basic helix-loop-helix (bHLH), and NAC families, have been well-characterized through genetic, molecular, and biochemical analyses (Wang et al, 2003; Golldack et al, 2011). Transgenic plants overexpressing these TFs show improved tolerance to different environmental stresses (Hossain M. et al, 2010). Overexpressing AtABF3 in alfalfa (Medicago sativa) reduces the transpiration rate and accumulation of reactive oxygen species, and increases tolerance to drought, salt, and oxidative stresses (Wang Z. et al, 2016)

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Discussion

Conclusion