LcSHMT4 from Sheepgrass Improves Tolerance to Cadmium and Manganese and Enhances Cd and Mn Accumulation in Grains

Heavy metal contamination is a serious environmental problem worldwide, with substantial negative ecological and economic effects. Serine hydroxymethyltransferase (SHMT) is a key metabolic and photorespiratory enzyme in plant cells, and it is also involved in stress responses. In this study, <i>LcSHMT4</i> was isolated from sheepgrass (<i>Leymus chinensis</i> (Trin.) Tzvel) after transcriptome sequence analysis. The transcript levels of <i>LcSHMT4</i> in sheepgrass seedlings increased under Cd and Mn stresses, and subcellular localization analysis in tobacco leaves revealed that its encoded protein localizes at the mitochondria. Transgenic yeast and rice lines overexpressing <i>LcSHMT4</i> showed increased tolerance to Cd and Mn, compared with that of their controls. In addition, compared with the control, transgenic rice overexpressing <i>LcSHMT4</i> accumulated more Cd and Mn in brown rice grains. The transcript levels of genes encoding Cd or Mn transporters were increased in the <i>LcSHMT4</i>-overexpressing transgenic rice lines. We speculate that LcSHMT4 may enhance Cd and Mn tolerance by increasing the activities of antioxidant enzymes and the glutathione content and increase heavy metal accumulation by inducing the expression of genes encoding transporters. These results highlight useful genetic resources and provide a theoretical basis for further research on heavy metal tolerance and the phytoremediation of heavy-metal-contaminated soil.