Genome-Wide Identification of Natural Resistance-Associated Macrophage Protein (NRAMP) and Expression Analysis Under Heavy Metal Stress in Sorghum bicolor L.

The NRAMP (Natural Resistance-Associated Macrophage Protein) family plays a pivotal role as membrane transporters in plants' responses to heavy metal stress. This study identified 12 <i>NRAMP</i> genes in <i>Sorghum bicolor</i> (sorghum) and performed a comprehensive bioinformatics analysis. The <i>SbNRAMP</i> genes are distributed across seven sorghum chromosomes. In-depth analyses of gene structure, conserved motifs, collinearity, and phylogeny indicated that the <i>SbNRAMP</i> family is divided into three subfamilies, each exhibiting unique structural and motif characteristics. Collinearity analysis suggested that large-fragment duplications, rather than tandem duplications, were responsible for the expansion of the <i>SbNRAMP</i> family, resulting in a greater number of genes compared to <i>Arabidopsis thaliana</i> and rice. Transcriptome analysis of the aboveground and underground parts of sorghum seedlings under saline-alkali stress revealed that <i>SbNRAMP5</i> is a key hub gene exhibiting tissue-specific expression. Furthermore, qRT-PCR analysis following exposure to Cd, Mn, or Zn treatments revealed differential expression among the <i>SbNRAMP</i> genes. Subcellular localization predictions indicated that all twelve NRAMPs are primarily located in the plasma membrane, with nine to twelve transmembrane domains, consistent with their function in metal ion transport. Experimental evidence confirmed that <i>SbNRAMP6</i> is localized in the plasma membrane. These findings establish a foundation for a deeper understanding of the structure and function of the sorghum <i>NRAMP</i> gene family.