Abscisic Acid Enhances Trehalose Content via <i>OsTPP3</i> to Improve Salt Tolerance in Rice Seedlings

Salt stress is one of the major environmental stresses that imposes constraints to plant growth and production. Abscisic acid (ABA) has been well-proven to function as a central integrator in plant under salt stress, and trehalose (Tre) has emerged as an excellent osmolyte to induce salt tolerance. However, the interacting mechanism between ABA and Tre in rice seedlings under salt stress is still obscure. Here, we found that the application of exogenous Tre significantly promoted the salt tolerance of rice seedlings by enhancing the activities of antioxidant enzymes. In addition, the expression of <i>OsNCED3</i> was significantly induced by salt stress. The overexpression of the <i>OsNCED3</i> gene enhanced the salt tolerance, while the knockout of <i>OsNCED3</i> reduced the salt tolerance of the rice seedlings. Metabolite analysis revealed that the Tre content was increased in the <i>OsNCED3</i>-overexpressing seedlings and reduced in the <i>nced3</i> mutant. The application of both ABA and Tre improved the salt tolerance of the nced3 mutant when compared with the WT seedling. <i>OsTPP3</i> was found to be induced by both the ABA and salt treatments. Consistent with the <i>OsNCED3</i> gene, the overexpression of <i>OsTPP3</i> enhanced salt tolerance while the knockout of <i>OsTPP3</i> reduced the salt tolerance of the rice seedlings. In addition, the Tre content was also higher in the <i>OsTPP3</i>-overexpressing seedling and lower in the <i>tpp3</i> mutant seedling than the WT plant. The application of exogenous Tre also enhanced the salt tolerance of the <i>tpp3</i> mutant plant. Overall, our results demonstrate that salt-increased ABA activated the expression of <i>OsTPP3</i>, which resulted in elevated Tre content and thus an improvement in the salt tolerance of rice seedlings.