Enhanced lanthanum stress tolerance of the transgenic <i>Arabidopsis</i> expressing <i>CnMT2</i> from <i>Chrysanthemum naktongense</i>

The rare earth element lanthanum (La) as a heavy metal can cause stress damage to plants at high concentrations. Metallothioneins (MTs) are low molecular weight proteins rich in cysteine and play significant roles in detoxification of metal ion stress in plants. In this study, we identified a novel function of CnMT2 from Chrysanthemum naktongense. Two MT homologous genes, namely CnMT2 and CnMT3, were cloned from the wild plant species C. naktongense, which exhibits high resistance to the rare earth element lanthanum (La). qRT-PCR analysis revealed that in C. naktongense, the highest expression level of CnMT2 occurred in roots. Its expression in stems, leaves, or shoot tips was also detected. Low expression levels of CnMT3 occurred in all tissues, with relatively higher expression levels in roots. LaCl 3 stress treatment could induce the expression of both CnMT2 and CnMT3, resulting in differential expression patterns between shoots and roots. Transgenic Arabidopsis seeds overexpressing CnMT2 exhibited increased resistance to LaCl 3 and H 2 O 2 during germination. Transgenic seedlings also exhibited growth enhancement with prolonged LaCl 3 stress, accompanied by significantly elevated enzyme activities of catalase and peroxidase. Our data revealed that CnMT2 from C. naktongense was able to enhance plant resistance to lanthanum and antioxidative capacity. Overall, the study unveiled a new function of CnMT2 in C. naktongense, which can be potentially used for engineering genotypes for phytoremediation.