Combining transcriptome and metabolome analyses to reveal the response of maize roots to Pb stress

As a major food crop, maize (Zea mays L.) is facing a serious threat of lead (Pb) pollution. Research into its Pb tolerance is crucial for ensuring food security and human health, however, the molecular mechanism underlying the response to Pb remains incompletely understood. Here, we investigated the transcriptomic and metabolome of two maize lines (BY001, a Pb-resistant line; BY006, a Pb-sensitive line) under different concentrations of Pb stress (0, 500, 1000, 2000 and 3000 mg/L). The results showed that BY001 performed well, whereas the BY006 exhibited minimal development of lateral roots upon exposure to high concentration of Pb. The antioxidant enzyme activity of BY001 remained relatively stable, while that of BY006 declined significantly. Transcriptomic analysis revealed that under high concentration of Pb stress, BY001 produced 5057 differentially expressed genes, whereas BY006 produced 3374. Functional annotation showed that these genes were primarily involved in carbohydrate metabolism, root growth, and plant resistance to external Pb stress. Further untargeted metabolomics indicated that Pb stress triggered distinct alterations in the levels of 47 diverse metabolite types across 13 distinct classes, particularly amino acids, carbohydrates, and organic acids. A conjoint omics analysis suggested that the pathways of starch and sucrose metabolism, as well as cutin, suberin, and wax biosynthesis in BY001, play a key role in the Pb resistance. These findings elucidate the biological mechanisms employed by maize to counter the effects of Pb stress, and provide a basis for breeding of maize cultivars with low Pb accumulation or tolerance.