Complex regulatory network of ZmbZIP54-mediated Pb tolerance in maize

Lead (Pb) is highly toxic and widely distributed in the soil, causing adverse effects on plant growth and yield formation. Herein, the combination of transmission electron microscope (TEM), energy dispersive X-ray Spectroscopy (EDS), and comparative transcriptome analyses was conducted to reveal the cytological mechanism and regulatory network of in the ZmbZIP54-mediated Pb tolerance in maize. As results, ZmbZIP54 helped in Pb²⁺ retention in the cell wall and intercellular space, inhibiting Pb²⁺ entering the cells and reducing its toxic effects on cell ultrastructure. Meanwhile, ZmbZIP54 was involved in the transition between the HCl-extracted and CH₃COOH-extracted Pb speciations. At the molecular level, ZmbZIP54 affected the macromolecule metabolism, thus decreasing Pb accumulation in the roots. Moreover, ZmZIFL1 and NRT1/PTR were the direct targets of ZmbZIP54, which participated in heavy metal binding, nitrogen uptaking, and IAA transport and thus mediated Pb transport, Pb speciation transition, and antioxidant enzyme activation. Collectively, we proposed a model to explain the complex regulatory network mediated by ZmbZIP54 and its target genes in maize tolerance to Pb stress.