Molecular Dissection of TaLTP1 Promoter Reveals Functional Cis-Elements Regulating Epidermis-Specific Expression

Guiping Wang,Silong Sun,Guanghui Yu,Hongwei Wang,Yongchao Hao,Xinxin Cheng,Jinxiao Zhao

doi:10.3390/ijms21072261

Guiping Wang, Silong Sun + Show 5 more

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https://doi.org/10.3390/ijms21072261

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Abstract

Plant epidermis serves important functions in shoot growth, plant defense and lipid metabolism, though mechanisms of related transcriptional regulation are largely unknown. Here, we identified cis-elements specific to shoot epidermis expression by dissecting the promoter of Triticum aestivum lipid transfer protein 1 (TaLTP1). A preliminary promoter deletion analysis revealed that a truncated fragment within 400 bp upstream from the translation start site was sufficient to confer conserved epidermis-specific expression in transgenic Brachypodium distachyon and Arabidopsis thaliana. Further, deletion or mutation of a GC(N4)GGCC motif at position −380 bp caused a loss of expression in pavement cells. With an electrophoretic mobility shift assay (EMSA) and transgenic reporter assay, we found that a light-responsive CcATC motif at position −268 bp was also involved in regulating pavement cell-specific expression that is evolutionary conserved. Moreover, expression specific to leaf trichome cells was found to be independently regulated by a CCaacAt motif at position −303 bp.

Highlights

Plant epidermis, representing the boundary between plants and their external environment, regulates the exchange of gas, water and nutrients and serves as a protective barrier [1,2]
We demonstrated that an expression cassette, comprised of the 898 bp upstream of the Triticum aestivum lipid transfer protein 1 (TaLTP1) translational start site fused to a GUS reporter gene, drives ubiquitous expression in the epidermal cell layer throughout the transgenic plant life cycle, especially in young growing shoot [20]
Quantitative and histochemical GUS analysis of TaLTP1 promoter deletion constructs showed that pavement cell and trichome expression are independently regulated by different TaLPT1 promoter cis-elements, wherein the quantitative expression in leaves was mainly attributable to that in pavement cells (Figure 1)

Summary

Introduction

Plant epidermis, representing the boundary between plants and their external environment, regulates the exchange of gas, water and nutrients and serves as a protective barrier [1,2]. In A. thaliana, regulatory networks with R2R3 Myb proteins (GL1/WER), bHLH-type transcription factors (GL3/EGL3), homeodomain-leucine zipper transcription factors (GL2) and a WD40 protein (TTG1) have been constructed for trichome and root hair formation [8]. Though ground epidermal cells cover most of the plant surface, little is known about their differentiation and its transcriptional regulation. The L1 box, which can be bound by homeodomain-leucine zipper IV transcription factors, has been demonstrated to be involved in regulating embryo epidermis gene expression [10,11]. Detailed dissection of the AtML1 promoter suggested that different cis-elements, rather than the L1 box, contribute to gene expression regulation at different developmental stages [10]. The MtML1 promoter from Medicago truncatula contributed epidermis-specific regulation in plant shoot, but functional cis-element analysis was not reported [12]

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