AlNAC4 Transcription Factor From Halophyte Aeluropus lagopoides Mitigates Oxidative Stress by Maintaining ROS Homeostasis in Transgenic Tobacco.

Jackson Khedia,Pradeep K Agarwal,Parinita Agarwal

doi:10.3389/fpls.2018.01522

Abstract

NAC proteins are a large family of plant-specific transcription factors which regulate both ABA-dependent and -independent gene expression. These transcription factors participate in biotic and abiotic stress-response through intricate regulation at transcriptional, post-transcriptional and post-translational levels. In the present study, AlNAC4 transcription factor was isolated from a salt excreting halophyte Aeluropus lagopoides. The AlNAC4 has an open reading frame of 936 bp, encoding a protein of 312 amino acid, with an estimated molecular mass of 34.9 kDa. The AlNAC4 showed close homology to monocot NACs in the phylogenetic tree. In silico analysis revealed that AlNAC4 possess the characteristic A-E subdomains within the NAC domain. The AlNAC4 showed sixteen post-translational phosphorylation sites. The AlNAC4 transcript was significantly upregulated with dehydration and H2O2 treatments, showing its role in osmotic and oxidative stress, respectively. The recombinant protein showed binding to mono as well as tandem repeats of NAC recognition sequence (NACRS) of the erd1 promoter. This is the first report mentioning that overexpression of AlNAC4 improved oxidative stress tolerance in tobacco transgenics. The transgenics maintained ROS homeostasis during H2O2 treatment. The transgenics showed regulation of stress-responsive genes including CAT, SOD, LEA5, PLC3, ERD10B, THT1 and transcription factors like AP2, ZFP during oxidative stress.Key Message: The AlNAC4 transcription factor from recretohalophyte Aeluropus showed regulation with abiotic stresses and binding to NACRS elements of erd1 promoter. The AlNAC4 tobacco transgenics showed improved growth with oxidative stress.

Highlights

The growth and development of sessile autotrophic plants is negatively affected by adverse environmental conditions
For stress tolerance study the seeds of tobacco wild type (WT) and T0 tobacco transgenic lines transformed with AlNAC4 gene (L33, L50 and L64) were germinated on Murashige and Skoog (1962) medium supplemented with NaCl (100, 200, and 300 mM) and mannitol (50, 100, 150, and 200 mM)
Phylogenetic relationships among some NAC proteins show that AlNAC4 gets clustered with stress-responsive MlNAC4, OsNAC4 and TaNAC4 proteins of the stress-related NAC (SNAC) group III (Figure 1B)

Summary

Introduction

The growth and development of sessile autotrophic plants is negatively affected by adverse environmental conditions. Plants manage stress-response via morphological, physiological and biochemical changes, involving expression of functional and regulatory genes for sustainable biological function (Hirayama and Shinozaki, 2010). The transcription factors (TFs) play a pivotal role in complex signaling network by regulating a large number of downstream genes (Zhang et al, 2011). The NACs are plant-specific TFs, involved in various biological processes including abiotic and biotic stress responses via both ABA-dependent and -independent stress signal transduction pathways (Nuruzzaman et al, 2013). The NAC TF coined by the initials of NAM (Petunia no apical meristem; Souer et al, 1996), ATAF1/2 (Arabidopsis thaliana transcription activation factor) and CUC2 (Arabidopsis cup-shaped cotyledon) proteins (Aida et al, 1997). The post-translational modifications like ubiquitination, dimerization, phosphorylation or proteolysis regulate NAC TFs activity (Kaneda et al, 2009; Miao et al, 2016)

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