A Novel Breeding Target for Salt-Tolerant Maize: ZmEXPA3 Overexpression Enhances Growth of Maize Under Both Non-Stressed and Salt Stress Conditions Through Cell-Wall Architecture Alteration

Expansins contribute to maize tolerance to salt stress, but the molecular mechanisms by which they function under high-salinity conditions remain poorly understood. In this research, the α-expansin gene <i>ZmEXPA3</i> was characterized. We obtained overexpression transgenic lines in maize and determined physiological and biochemical indices to elucidate its molecular role in salt stress. Our results confirmed that <i>ZmEXPA3</i> functioned as a positive salt tolerance regulator and was potentially regulated by abscisic acid (ABA) and methyl jasmonate (MeJA). ZmEXPA3 located to the cytoplasm and cell wall. Overexpression of <i>ZmEXPA3</i> achieved thicker cell wall and bigger cell size and thereby promoted biomass accumulation. The <i>ZmEXPA3-OE</i> lines showed a marked reduction in malondialdehyde (MDA) and H₂O₂ accumulation compared to the WT under salt stress. Overexpression of <i>ZmEXPA3</i> elevated the enzyme activity of peroxidase (POD) and superoxide dismutase (SOD) and proline accumulation and decreased the Na⁺/K⁺ ratio in roots. Transcriptome and Gene Ontology (GO) enrichment analysis of <i>ZmEXPA3-OE</i> lines and WT showed that many differentially expressed genes (DEGs) were enriched in cell-wall-related terms, plant hormone response, osmotic stress response, salt stress response, oxidoreductase activity, etc. Changes in these processes may be the primary reasons why <i>ZmEXPA3</i> overexpression promotes growth and salt tolerance.