<i>SOS3-3</i> Enhances the Salt Tolerance of Tomato Plants by Regulating ROS Balance

Salt stress affects the growth, metabolism, yield, and quality of crops. To adapt to high-salt environments, plants form various regulatory mechanisms. <i>Salt over sensitive</i> (<i>SOS</i>) is the key gene of SOS signal transduction pathway. As a member of the SOS3 subfamily, the function of <i>SOS3-3</i> under salt stress has not been reported. To verify the function of <i>SOS3-3</i> and the morphological and physiological parameters, the expression of genes related to stress were compared between the <i>SOS3-3</i> overexpressed (OE<i>SOS3-3</i>) and silenced tomato (V<i>SOS3-3</i>) at control and 10 days’ NaCl treatment. The results showed that, compared with the control (Ve), the plants of V<i>SOS3-3</i> were shorter under salt stress, with curled leaves and abscission. The fresh and dry weights, <i>F_v</i>/<i>F_m</i>, total chlorophyll content, antioxidant enzyme activities, and proline content of V<i>SOS3-3</i> significantly decreased, while the relative conductivity, hydrogen peroxide (H₂O₂), and Malondialdehyde (MDA) content of V<i>SOS3-3</i> plants significantly increased compared to that of WT, respectively. Compared to the wild-type (WT), OE<i>SOS3-3</i> plants were less damaged by salt stress, with significantly higher plant height, fresh and dry weights, <i>F_v</i>/<i>F_m</i>, total chlorophyll content, antioxidant enzyme activity, and proline content. However, the relative conductance, H₂O₂, and MDA content were significantly lower in OE<i>SOS3-3</i> than WT. The expression levels of <i>SOS1</i>, <i>SOS2</i>, <i>LKT1</i> (ion transport-related gene), <i>APX1</i> (ROS signaling pathway-related gene), <i>P5CS</i> (osmoregulation-related gene), and <i>ABF4</i> (ABA signaling pathway-related gene) were significantly lower in V<i>SOS3-3</i> than Ve, but significantly higher in OE<i>SOS3-3</i> than in WT. These results suggested that <i>SOS3-3</i> regulate salt tolerance by influencing physiological and biochemical changes and the expression of genes related to stress response. This study revealed the mechanism of <i>SOS</i> family participating in regulating tomato salt tolerance, providing a theoretical basis for improving tomato salt tolerance.