Genome-Wide Characterization and Expression Analysis of Soybean TGA Transcription Factors Identified a Novel TGA Gene Involved in Drought and Salt Tolerance.

Bo Li,Jin-Dong Fu,Ying Liu,Ming Chen,Long-Guo Jin,You-Zhi Ma,Xi-Yan Cui,Wei-Jun Zheng,Dong-Hong Min,Jin-Hao Lan,Zhao-Shi Xu,Yong-Bin Zhou

doi:10.3389/fpls.2019.00549

Abstract

The TGA transcription factors, a subfamily of bZIP group D, play crucial roles in various biological processes, including the regulation of growth and development as well as responses to pathogens and abiotic stress. In this study, 27 TGA genes were identified in the soybean genome. The expression patterns of GmTGA genes showed that several GmTGA genes are differentially expressed under drought and salt stress conditions. Among them, GmTGA17 was strongly induced by both stress, which were verificated by the promoter-GUS fusion assay. GmTGA17 encodes a nuclear-localized protein with transcriptional activation activity. Heterologous and homologous overexpression of GmTGA17 enhanced tolerance to drought and salt stress in both transgeinc Arabidopsis plants and soybean hairy roots. However, RNAi hairy roots silenced for GmTGA17 exhibited an increased sensitivity to drought and salt stress. In response to drought or salt stress, transgenic Arabidopsis plants had an increased chlorophyll and proline contents, a higher ABA content, a decreased MDA content, a reduced water loss rate, and an altered expression of ABA- responsive marker genes compared with WT plants. In addition, transgenic Arabidopsis plants were more sensitive to ABA in stomatal closure. Similarly, measurement of physiological parameters showed an increase in chlorophyll and proline contents, with a decrease in MDA content in soybean seedlings with overexpression hairy roots after drought and salt stress treatments. The opposite results for each measurement were observed in RNAi lines. This study provides new insights for functional analysis of soybean TGA transcription factors in abiotic stress.

Highlights

Abiotic stress, such as drought and high salinity, greatly affect plant growth and development
Full-length proteins and conserved domains of 10 Arabidopsis TGAs were used as BLAST query sequences against the soybean genome database
A total of 27 non-redundant, putative TGA genes were identified in the soybean genome, which named GmTGA01-GmTGA27 according to the Gene ID number (Table 1)

Summary

Introduction

Abiotic stress, such as drought and high salinity, greatly affect plant growth and development. Changes in gene expression are the earliest responses in plants, and a number of stressresponsive genes have been noted to have important functions in drought and salt resistance. Among these genes, transcription factors are very important as the proteins they typically encode control the transcription of downstream genes (Singh et al, 2002; Li et al, 2008). Tobacco TGA1a was the first TGA transcription factor cloned from plants and is characterized by the conserved basic region/leucine zipper domain (Katagiri et al, 1989). For TGA proteins, the primary structure of the bZIP domain is conserved, containing an invariant motif N-x7R/K-x9-L-x6-L-x6-L in the N-terminus, and a bZIP-D box, the motif Yx2RL[RQ]ALSS[LS]W, represents the signature domain of group D in the C-terminus (Jakoby et al, 2002)

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Discussion

Conclusion