Integrated physiological, transcriptomic and metabolomic analysis revealed heterosis for cadmium tolerance in maize

Heterosis refers to the phenomenon whereby the performance of F 1 hybrids exceeds their parents in yield and stress tolerance, yet the underlying mechanism under abiotic stress remains further elucidated in maize. This study conducted an integrated physiological, transcriptomic, and metabolomic analysis for the hybrid Zhengdan958 (ZD958) and its parents under cadmium (Cd) stress. ZD958 exhibited consistently superior performance across all morphological traits under Cd stress. Additionally, ZD958 demonstrated significant heterosis in the activity of superoxide dismutase and catalase under Cd stress. Further analysis revealed 904 unique differentially expressed genes in ZD958 under Cd stress, and weighted gene co-expression network analysis of these genes identified two modules. Metabolomic analysis identified 902 metabolites, and the differentially accumulated metabolites in ZD958 primarily enriched in phenylpropanoid biosynthesis, glycerophospholipid metabolism, and glycosylphosphatidylinositol-anchor biosynthesis. Analysis of non-additive expression (NAE) genes identified one gene under both control and Cd stress, which was also specifically down-regulated in ZD958 under Cd stress. Analysis of allele-specific expression (ASE) genes identified 12 genetically over-dominant genes in ZD958. Integrated analysis highlighted the critical roles of phenylpropanoid biosynthesis and starch and sucrose metabolism in the heterosis of ZD958 to Cd stress. Our study would deepen the understanding of the mechanism underlying heterosis to Cd stress, and offer potential target genes for improving Cd tolerance in maize.