Functional divergence of MdMYB123 and its truncated variant modulates Cd uptake and detoxification in apple

Cadmium (Cd) is a globally distributed environmental contaminant that accumulates in agricultural soils, threatening crop productivity and food safety. In this study, we investigated the roles of the apple transcription factor MdMYB123 and its truncated variant, mdmyb123, in Cd tolerance. Cd exposure significantly induced the expression of both genes. Functional analyses in overexpressing apple lines revealed opposite roles: MdMYB123-overexpression (OE) enhanced Cd tolerance, whereas mdmyb123-oe increased Cd sensitivity. Compared to the wild type, MdMYB123-OE plants accumulated less Cd and exhibited lower malondialdehyde (MDA) and reactive oxygen species (ROS) levels, accompanied by stronger activation of antioxidant enzymes (SOD, POD, and CAT). Conversely, mdmyb123-OE lines showed higher Cd accumulation, increased oxidative stress, and reduced antioxidant activity. Transcriptome analysis identified MdALMT1 and MdtDT as downstream targets. Yeast one-hybrid, GUS/LUC reporter, and ChIP-qPCR assays confirmed that both MdMYB123 and mdmyb123 bind to the CAACTG motif in the promoters of MdALMT1 and MdtDT, however, only the MdMYB123 activated their transcription. Functional validation in yeast and Arabidopsis demonstrated that overexpression of MdALMT1 and MdtDT enhanced Cd tolerance. Collectively, our findings demonstrate that MdMYB123 improves Cd tolerance by activating genes involved in vacuolar sequestration and limiting Cd uptake, suggesting its potential utility for breeding or engineering Cd-safe apple cultivars.