Functional Characterization of MeJA-Induced OjTIFY2 in Mediating Salt Stress Tolerance in Oenanthe javanica

The plant-specific transcription factor TIFY plays key roles in plant growth and development, including seed germination, signal transduction, and responses to environmental stimuli and plant hormones. However, few studies have investigated the function of the TIFY family in responding to salinity stress in water dropwort (Oenanthe javanica (Blume) D.C). Here, a total of 24 OjTIFY genes, named OjTIFY1-OjTIFY24, were identified in water dropwort. And their phylogenetic relationships, gene structure, chromosomal distribution, promoter regions, and collinearity patterns were comprehensively analyzed. We further identified a member, OjTIFY2, located in the nucleus and positively upregulated by exogenous MeJA. Meanwhile, we found that exogenous MeJA could alleviate the sensitivity of water dropwort to salt stress by regulating the activity of antioxidant enzymes and the content of osmotic regulatory substances. A transient overexpression experiment in water dropwort showed that OjTIFY2 enhanced its tolerance to salt stress. The qRT-PCR analysis showed that OjSOS1, OjSOS3, OjKAT1, OjP5CS, and OjHKT1 were significantly upregulated when OjTIFY2-overexpressing lines were subjected to salt stress. Then, the transgenic Arabidopsis overexpressing OjTIFY2 also exhibited tolerance to salt stress by increasing the activities of SOD, POD, and CAT, and the contents of proline and chlorophyll, and by reducing the contents of MDA and H₂O₂. We also found that OjTIFY2 positively regulates the expression of salt-stress-related genes AtSOS1, AtSOS3, AtKAT1, AtP5CS, and AtHKT1. These results suggest that OjTIFY2 acts as a positive regulator of salt tolerance in water dropwort by modulating ROS scavenging and the expression of salt-related genes.