ThNAC13, a NAC Transcription Factor from Tamarix hispida, Confers Salt and Osmotic Stress Tolerance to Transgenic Tamarix and Arabidopsis.

Liuqiang Wang,Mengzhu Lu,Yucheng Wang,Zhen Li

doi:10.3389/fpls.2017.00635

Abstract

NAC (NAM, ATAF1/2, and CUC2) proteins play critical roles in many plant biological processes and environmental stress. However, NAC proteins from Tamarix hispida have not been functionally characterized. Here, we studied a NAC gene from T. hispida, ThNAC13, in response to salt and osmotic stresses. ThNAC13 is a nuclear protein with a C-terminal transactivation domain. ThNAC13 can bind to NAC recognized sites and calmodulin-binding NAC (CBNAC) binding element. Overexpression of ThNAC13 in Arabidopsis improved seed germination rate and increased root growth and fresh weight gain under salt or osmotic stress. Transgenic T. hispida plants transiently overexpressing ThNAC13 and with RNAi-silenced ThNAC13 were generated for gain- and loss-of-function experiments. Following exposure to salt or osmotic stress, overexpression of ThNAC13 induced superoxide dismutase (SOD) and peroxidase (POD) activities, chlorophyll and proline contents; decreased the reactive oxygen species (ROS) and malondialdehyde levels; and reduced electrolyte leakage rates in both transgenic Tamarix and Arabidopsis plants. In contrast, RNAi-silenced ThNAC13 showed the opposite results in transgenic Tamarix. Furthermore, ThNAC13 induced the expression of SODs and PODs in transgenic Arabidopsis. These results suggest that ThNAC13 improves salt and osmotic tolerance by enhancing the ROS-scavenging capability and adjusting osmotic potential.

Highlights

Transcriptional regulation plays crucial roles in controlling plant biological processes and signaling pathways, and transcription factors interact with promoter elements of target genes to activate or repress their transcription (Pérez-Rodríguez et al, 2009; Shang et al, 2013)
Total RNA was isolated from leaves of T. hispida and Arabidopsis plants using a CTAB method (Chang et al, 1993)
The first-strand cDNA was synthesized using the PrimeScriptTM RT reagent Kit (TaKaRa, China), and the real-time RT-PCR was performed in the Opticon 2 System (Bio-Rad, Hercules, CA, USA) following the protocol described by Wang et al (2014b)

Summary

Introduction

Transcriptional regulation plays crucial roles in controlling plant biological processes and signaling pathways, and transcription factors interact with promoter elements of target genes to activate or repress their transcription (Pérez-Rodríguez et al, 2009; Shang et al, 2013). The Arabidopsis NAC016 can repress the transcripts of ABSCISIC ACID-RESPONSIVE ELEMENT BINDING PROTEIN 1 (AREB1), which is a key transcription factor in the ABA-dependent stress-signaling pathway, and promote responses to drought stress (Sakuraba et al, 2015). Hong et al (2016) demonstrated that ONAC022 expression was a response to abiotic stress, and transgenic rice overexpressing ONAC022 showed enhanced tolerance to drought and salt stresses by modulating the ABA signaling pathway. Overexpression of SNAC3 in transgenic rice conferred tolerance to high temperature, drought and oxidative stresses through modulation of ROS scavenging pathways. TaNAC29 and TaNAC67 are up-regulated under different abiotic stresses, and transgenic Arabidopsis plants expressing these genes showed increased salt and drought tolerance (Mao et al, 2014; Huang et al, 2015). A NAC-type transcription factor from chickpea, CarNAC4, induces the expression of genes involved in stress tolerance, including DREB2A, COR15A, RD29A, and KIN1, which increased tolerance to salt and drought stresses (Yu et al, 2016)

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