Genome-Wide Identification of Metal Tolerance Protein Genes in Populus trichocarpa and Their Roles in Response to Various Heavy Metal Stresses.

Yongfeng Gao,Fengming Yang,Jikai Liu,Lin Zhang,Yongbin Ou,Zihao Chen,Wang Xie,Yinan Yao,Zhuoxi Peng

doi:10.3390/ijms21051680

Yongfeng Gao, Fengming Yang + Show 7 more

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https://doi.org/10.3390/ijms21051680

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Abstract

Metal tolerance proteins (MTPs) are plant divalent cation transporters that play important roles in plant metal tolerance and homeostasis. Poplar is an ideal candidate for the phytoremediation of heavy metals because of its numerous beneficial attributes. However, the definitive phylogeny and heavy metal transport mechanisms of the MTP family in poplar remain unknown. Here, 22 MTP genes in P. trichocarpa were identified and classified into three major clusters and seven groups according to phylogenetic relationships. An evolutionary analysis suggested that PtrMTP genes had undergone gene expansion through tandem or segmental duplication events. Moreover, all PtrMTPs were predicted to localize in the vacuole and/or cell membrane, and contained typical structural features of the MTP family, cation efflux domain. The temporal and spatial expression pattern analysis results indicated the involvement of PtrMTP genes in poplar developmental control. Under heavy metal stress, most of PtrMTP genes were induced by at least two metal ions in roots, stems or leaves. In addition, PtrMTP8.1, PtrMTP9 and PtrMTP10.4 displayed the ability of Mn transport in yeast cells, and PtrMTP6 could transport Co, Fe and Mn. These findings will provide an important foundation to elucidate the biological functions of PtrMTP genes, and especially their role in regulating heavy metal tolerance in poplar.

Highlights

Heavy metal pollution is becoming a more and more serious problem globally
By using the sequences of 12 AtMTP proteins as queries, we identified a total of 22 Metal tolerance proteins (MTPs) genes in P. trichocarpa genome, three more than previous results [20]
We summarized the PtrMTP genes in each tissue with expression changes over four times: In root, Cd enhanced the expression of PtrMTP11.1; Cu increased the expression levels of PtrMTP8.1 and PtrMTP10.3, but decreased the expression levels of PtrMTP9; Mn repressed the expression levels of PtrMTP9 and PtrMTP10.3; Ni repressed the expression levels of PtrMTP10.3, but Zn enhanced its expression

Summary

Introduction

Heavy metal pollution is becoming a more and more serious problem globally. It poses a grave risk for food and environmental safety, as well as human health [1]. Some plants have hyperaccumulation and/or hypertolerance characteristics for specific heavy metals, and are excellent candidates for phytoremediation to reduce environmental heavy metal pollutant levels. These plants must possess a distinct system that contributes to the high capacity of heavy metal enrichment and tolerance, including metal uptake, efflux, chelation, translocation, intracellular sequestration and storage; among these, the metal transporters play a crucial role [3,4]. Since the identification of Cupriavidus metallidurans in 1995, increasing numbers of CDF genes have been cloned, functionally investigated and classified into three clusters: Zn-CDF, Fe/Zn-CDF and Mn-CDF [5,6]

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