Genome-Wide Characterization of Sedum plumbizincicola HMA Gene Family Provides Functional Implications in Cadmium Response

Abstract

Heavy-metal ATPase (<i>HMA</i>), an ancient family of transition metal pumps, plays important roles in the transmembrane transport of transition metals such as Cu, Zn, Cd, and Co. Although characterization of <i>HMAs</i> has been conducted in several plants, scarcely knowledge was revealed in <i>Sedum plumbizincicola</i>, a type of cadmium (Cd) hyperaccumulator found in Zhejiang, China. In this study, we first carried out research on genome-wide analysis of the <i>HMA</i> gene family in <i>S. plumbizincicola</i> and finally identified 8 <i>SpHMA</i> genes and divided them into two subfamilies according to sequence alignment and phylogenetic analysis. In addition, a structural analysis showed that <i>SpHMAs</i> were relatively conserved during evolution. All of the <i>SpHMAs</i> contained the <i>HMA</i> domain and the highly conserved motifs, such as DKTGT, GDGxNDxP, PxxK S/TGE, HP, and CPx/SPC. A promoter analysis showed that the majority of the <i>SpHMA</i> genes had cis-acting elements related to the abiotic stress response. The expression profiles showed that most <i>SpHMAs</i> exhibited tissue expression specificity and their expression can be regulated by different heavy metal stress. The members of Zn/Co/Cd/Pb subgroup (<i>SpHMA1</i>-<i>3</i>) were verified to be upregulated in various tissues when exposed to CdCl₂. Here we also found that the expression of <i>SpHMA7</i>, which belonged to the Cu/Ag subgroup, had an upregulated trend in Cd stress. Overexpression of <i>SpHMA7</i> in transgenic yeast indicated an improved sensitivity to Cd. These results provide insights into the evolutionary processes and potential functions of the <i>HMA</i> gene family in <i>S. plumbizincicola</i>, laying a theoretical basis for further studies on figuring out their roles in regulating plant responses to biotic/abiotic stresses.