Characterization of VuMATE1 Expression in Response to Iron Nutrition and Aluminum Stress Reveals Adaptation of Rice Bean (Vigna umbellata) to Acid Soils through Cis Regulation.

Meiya Liu,Wei Fan,Jianli Yang,Jiameng Xu,Shaojian Zheng,Heqiang Lou

doi:10.3389/fpls.2016.00511

Abstract

Rice bean (Vigna umbellata) VuMATE1 appears to be constitutively expressed at vascular system but root apex, and Al stress extends its expression to root apex. Whether VuMATE1 participates in both Al tolerance and Fe nutrition, and how VuMATE1 expression is regulated is of great interest. In this study, the role of VuMATE1 in Fe nutrition was characterized through in planta complementation assays. The transcriptional regulation of VuMATE1 was investigated through promoter analysis and promoter-GUS reporter assays. The results showed that the expression of VuMATE1 was regulated by Al stress but not Fe status. Complementation of frd3-1 with VuMATE1 under VuMATE1 promoter could not restore phenotype, but restored with 35SCaMV promoter. Immunostaining of VuMATE1 revealed abnormal localization of VuMATE1 in vasculature. In planta GUS reporter assay identified Al-responsive cis-acting elements resided between -1228 and -574 bp. Promoter analysis revealed several cis-acting elements, but transcription is not simply regulated by one of these elements. We demonstrated that cis regulation of VuMATE1 expression is involved in Al tolerance mechanism, while not involved in Fe nutrition. These results reveal the evolution of VuMATE1 expression for better adaptation of rice bean to acid soils where Al stress imposed but Fe deficiency pressure released.

Highlights

Multidrug and toxic compound extrusion (MATE) protein forms a large family of transporters in prokaryotes and eukaryotes where they perform a broad range of functions with diverse substrates (Omote et al, 2006)
We further demonstrate that cis-regulation is involved in Al-induced expression of VuMATE1, and the cis-acting elements involved in root-tip-specific and Al-inducible expression of VuMATE1 resided in promoter region between −1228 and −574 bp
We demonstrated that cis regulation is involved in the transcriptional regulation of VuMATE1 expression in adaptation to acid soils

Summary

Introduction

Multidrug and toxic compound extrusion (MATE) protein forms a large family of transporters in prokaryotes and eukaryotes where they perform a broad range of functions with diverse substrates (Omote et al, 2006). One role is involved in the translocation of iron (Fe) from the roots to the shoots, such as Ferric Reductase Deficient 3 (FRD3) in Arabidopsis (Durrett et al, 2007) and OsFRDL1 (for FRD3like 1) in rice (Oryza sativa; Yokosho et al, 2009) These proteins are mainly expressed in the pericycle where they transport citrate into the xylem. The second role for this sub-group of MATE proteins involves in Al3+ tolerance, such as HvAACT1 (Aluminum-activated citrate transporter 1) in barley (Hordeum vulgare; Furukawa et al, 2007) and SbMATE in sorghum (Sorghum bicolor; Magalhaes et al, 2007) These proteins are expressed in the root apices and they facilitate the Al3+-activated secretion of citrate which protects the growing root apices from Al3+ toxicity in acid soils. These findings are consistent with the hypothesis that the original functions of these genes are altered or extended by mutations to the coding or regulatory regions of the gene (Ryan and Delhaize, 2010)

Methods

Results

Conclusion