Transcriptomic reprogramming underlies melatonin-mediated enhancement of cadmium tolerance and lateral root growth in...

Soil contamination by heavy metals, particularly cadmium (Cd), poses a serious threat to sustainable soybean (Glycine max) production and food safety. Melatonin (MT) has been reported to enhance plant tolerance to abiotic stress; however, the molecular mechanisms underlying MT-mediated Cd tolerance and cultivar-specific responses in soybean remain largely unclear. Here, comparative transcriptome analysis, weighted gene co-expression network analysis (WGCNA) and physio-biochemical assays were integrated to investigate the regulatory mechanisms of MT-mediated Cd tolerance in soybean. Exogenous melatonin (exMT) application significantly reduced Cd accumulation in roots and shoots by 40% and 38%, respectively, while concomitantly enhancing the antioxidant system. Moreover, treatment with 10 μM exMT markedly improved plant growth, increasing primary root length, stem length, lateral root number, chlorophyll content and fresh weight by 14, 49, 16, 63 and 18%, respectively. WGCNA revealed that Cd stress triggered a core regulatory network involving MYB36, the senescence-related gene SRG1, the peroxidase gene PRX5, the polyamine oxidase gene PPO and the mitochondrial phosphate transporter gene PiC, which collectively contributed to Cd-induced toxicity. In contrast, integrated analyses identified a distinct regulatory module associated with MT-mediated Cd tolerance, including key genes such as DTX14, CSLA9 and ERF72. Furthermore, different soybean cultivars exhibited pronounced genotype-dependent Cd tolerance, which was closely correlated with endogenous MT levels. Our findings could advance understanding of the genetic basis of Cd tolerance and facilitate the breeding of low-Cd-accumulating soybean cultivars.