Heavy Metal Stress-Associated Proteins in Rice and Arabidopsis: Genome-Wide Identification, Phylogenetics, Duplication, and Expression Profiles Analysis

Abstract

Heavy metal exposure is a serious environmental stress in plants. However, plants have evolved several strategies to improve their heavy metal tolerance. Heavy metal-associated proteins (HMPs) participate in heavy metal detoxification. Here, we identified 46 and 55 HMPs in rice and <i>Arabidopsis</i>, respectively, and named them OsHMP 1-46 and AtHMP 1-55 according to their chromosomal locations. The HMPs from both plants were divided into six clades based on the characteristics of their heavy metal-associated domains (HMA). The HMP gene structures and motifs varied greatly among the different classifications. The HMPs had high collinearity and were segmentally duplicated. A <i>cis</i>-element analysis revealed that the HMPs may be regulated by different transcription factors. An expression profile analysis disclosed that only eight OsHMPs were constitutive in rice tissues. Of these, the expression of <i>OsHMP37</i> was far higher than that of the other seven genes while <i>OsHMP28</i> was expressed exclusively in the roots. For <i>Arabidopsis</i>, nine <i>AtHMP</i>s presented with very high transcript levels in all organs. Most of the selected <i>OsHMP</i>s were differentially expressed in various tissues under different heavy metal stresses. Only <i>OsHMP09, OsHMP18</i>, and <i>OsHMP22</i> showed higher expression levels in all tissues under different heavy metal stresses. In contrast, most of the selected <i>AtHMP</i>s had nearly constant expression levels in different tissues under various heavy metal stresses. The <i>AtHMP20, AtHMP23, AtHMP25, AtHMP31, AtHMP35, AtHMP46</i> expression levels under different heavy metal stresses were higher in the leaves and roots. The foregoing discoveries elucidated HMP evolution in monocotyledonous and dicotyledonous plants and may helpful functionally characterize HMPs in the future.