Overexpression of the Wheat Expansin Gene TaEXPA2 Improved Seed Production and Drought Tolerance in Transgenic Tobacco Plants.

Yanhui Chen,Meng Zhang,Shan Zhou,Xiangzhu Kong,Yangyang Han,Wei Wang,Zhi Min Yang

doi:10.1371/journal.pone.0153494

Yanhui Chen, Meng Zhang + Show 5 more

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https://doi.org/10.1371/journal.pone.0153494

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Abstract

Expansins are cell wall proteins that are grouped into two main families, α-expansins and β-expansins, and they are implicated in the control of cell extension via the disruption of hydrogen bonds between cellulose and matrix glucans. TaEXPA2 is an α-expansin gene identified in wheat. Based on putative cis-regulatory elements in the TaEXPA2 promoter sequence and the expression pattern induced when polyethylene glycol (PEG) is used to mimic water stress, we hypothesized that TaEXPA2 is involved in plant drought tolerance and plant development. Through transient expression of 35S::TaEXPA2-GFP in onion epidermal cells, TaEXPA2 was localized to the cell wall. Constitutive expression of TaEXPA2 in tobacco improved seed production by increasing capsule number, not seed size, without having any effect on plant growth patterns. The transgenic tobacco exhibited a significantly greater tolerance to water-deficiency stress than did wild-type (WT) plants. We found that under drought stress, the transgenic plants maintained a better water status. The accumulated content of osmotic adjustment substances, such as proline, in TaEXPA2 transgenic plants was greater than that in WT plants. Transgenic plants also displayed greater antioxidative competence as indicated by their lower malondialdehyde (MDA) content, relative electrical conductivity, and reactive oxygen species (ROS) accumulation than did WT plants. This result suggests that the transgenic plants suffer less damage from ROS under drought conditions. The activities of some antioxidant enzymes as well as expression levels of several genes encoding key antioxidant enzymes were higher in the transgenic plants than in the WT plants under drought stress. Collectively, our results suggest that ectopic expression of the wheat expansin gene TaEXPA2 improves seed production and drought tolerance in transgenic tobacco plants.

Highlights

The expansins are a multigene family that includes the α-expansin (EXPA), β-expansin (EXPB), expansin-like A, and expansin-like B subfamilies
The transgenic plants consistently had 1.5-fold to 1.8-fold higher levels of expansin activity than the WT plants (Fig 3C). These results demonstrated that the TaEXPA2 gene was successfully introduced into the tobacco plants and it substantially increased the activity of expansin
We examined the functions of TaEXPA2 in drought stress tolerance using our transgenic tobacco lines

Summary

Introduction

The expansins are a multigene family that includes the α-expansin (EXPA), β-expansin (EXPB), expansin-like A, and expansin-like B subfamilies. The amino acid sequences of the expansin proteins in these four subfamilies exhibit only 20–40% identity. EXPA and EXPB, the two major groups, share several conserved motifs and likely have similar, but different, functions [1]. Analysis of the gene structures and predicted amino acid sequences of rice and Arabidopsis expansins indicates that the α- and β-expansin genes evolved from one ancestral gene. The exon/intron organization is unchanged, but the length of each intron and the number of introns differs among the individual genes [2,3]. It is believed that the functions of the α- and β-expansin genes are similar and different in a number of ways. By contrast, increased in both transgenic Arabidopsis lines, but the mechanisms of this increase were different, as seen by the differing transcription levels of two stress-associated genes, COR15a and KIN1, hours after salt treatment [4]

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