Overexpression of Maize Expansin Gene ZmEXPA6 Improves Salt Tolerance of Arabidopsis thaliana

Maize is a globally vital crop for both grain and forage production. Its cultivation and growth are significantly restricted by salt stress. Expansins are non-enzymatic plant cell wall proteins that play pivotal roles in growth, development, and stress responses by mediating cell wall loosening. We identified ZmEXPA6, an α-expansin gene, as exhibiting high expression levels in maize roots under salt stress. In this study, the ZmEXPA6 gene was cloned and functionally characterized. Heterologous overexpression of ZmEXPA6 promoted root elongation and enhanced salt tolerance of Arabidopsis thaliana. Under salt stress, the ZmEXPA6 overexpression lines exhibited elevated levels of anthocyanin (61.70%, 59.70%), proline (16.39%, 15.11%), soluble sugars (11.97%, 8.68%), and soluble proteins (14.83%, 13.74%) compared to the WT. Concurrently, the expression of genes associated with anthocyanin and proline biosynthesis was markedly up-regulated in these overexpression lines. The ZmEXPA6 overexpression lines exhibited elevated activities of SOD (23.81%, 23.51%), CAT (13.86%, 10.93%), and POD (4.27%, 1.39%) compared to the WT, along with significantly reduced accumulation of MDA (23.47%, 24.48%), O2− (21.9%, 19.8%), and H2O2 (27.61%, 18.07%). These results indicate that ZmEXPA6 is involved in the growth and development of Arabidopsis thaliana and improves its salt tolerance through enhanced osmotic adjustment and elevated antioxidant capacity.