The Lipoxygenase Gene AfLOX4 of Amorpha Fruticosa L . is a Potential Regulator of Drought Stress Tolerance Pathways under Saline and Alkaline Conditions

Lipoxygenase (LOX, EC1.13.11.12) catalyzes the oxygenation of polyunsaturated fatty acids and further generates oxylipins via enzymatic or non-enzymatic pathways, thus participating in the regulation of growth and development, stress response, and other processes. The objective of this research was to characterize the function and evaluate the mechanism of lipoxygenase gene AfLOX4 ’s role in enhancing drought tolerance. Transcriptomic data were generated and analyzed for the LOX gene, under different concentrations of drought (polyethylene glycol-6000) (PEG6000) and abscisic acid (ABA) stress treatment, to determine their effects on the expression of the AfLOX4 gene and its role in plant physiology. The localization of the AfLOX4 protein was detected through protoplast transformation. The expression of AfLOX4 in Amorpha fruticosa tissues was determined by quantitative real-time PCR (qRT-PCR). Six LOX genes of A. fruticosa that showed an upregulated pattern under different concentrations of drought (PEG6000) stress were found via transcriptomic analysis and were named AfLOX1 ~ 6. The AfLOX4 protein was localized in the cytoplasm. AfLOX4 was expressed in the stems, roots, flowers, and leaves of Amorpha fruticosa L., and its expression level was the highest in leaves. The expression of AfLOX4 increased with the prolongation of stress time under different stresses. After ABA treatment, the germination rate of tobacco lines overexpressing AfLOX4 was significantly increased, while under NaHCO 3 stress, the tolerance of tobacco plants overexpressing AfLOX4 was higher than that of wild-type tobacco. The tobacco with overexpression of the AfLOX4 gene detected by the natural drought method had a higher survival rate in the drought stress recovery experiment, and improved the drought tolerance of tobacco. This study reveals the function of the AfLOX4 gene in resisting drought stress and lays a solid theoretical foundation for the genetic improvement of Amorpha fruticosa L. plant varieties, as well as improvement of resource utilization.