Effect of Exogenous Cadaverine Phosphate on Plant Growth, Photosynthesis, and Gene Expression of Lettuce Seedlings

Excessive use of treatment chemicals and fertilizers poses a severe threat to agricultural productivity. The development of novel biobased foliar agents is the best environmentally and economically viable option to promote plant growth and alleviate salt stress toxicity. The potential role of cadaverine phosphate (CP) in the productivity, photosynthesis, and transcriptional expression in lettuce (Lactuca sativa L. var. ramosa Hort.) seedlings grown in saline and non-saline soils in the greenhouse was investigated. Under normal growth conditions, the application of 1 g L⁻¹ CP promoted lettuce growth in pot experiments, but this effect was not evident under salt-stress conditions. After 24 h of spraying with CP, the net photosynthetic rate increased significantly by 75 and 46.5% under normal and saline conditions, respectively, compared with the distilled water control. RNA-seq analysis revealed 486 and 104 differentially expressed genes (DEGs) in the shoots and roots at 6 h and 31 and 117 DEGs at 24 h, respectively. Kyoto Encyclopedia of Genes and Genomes enrichment analysis showed that CP could regulate genetic expression in association with sesquiterpenoid and triterpenoid biosynthesis, phenylpropanoid biosynthesis, cyanoamino acid metabolism, plant hormone signal transduction, mitogen-activated protein kinase signaling pathway, and photosynthesis. Overall, CP enhanced the photosynthetic capacity, induced stress alleviation genes, and consequently achieved a growth-promoting effect on lettuce. This study provides insights into the molecular mechanisms underlying plant growth promotion by CP, which may be useful for enhancing the stability of biofertilizer applications in plants.