Endophytic Colonization of Beauveria bassiana Enhances Drought Stress Tolerance in Tomato via the “Water Spender” Pathway

Drought stress is one of the most important climate-related factors affecting crop production. Tomatoes (Solanum lycopersicum L.) are economically important crop which are highly sensitive to drought. The entomopathogenic fungus Beauveria bassiana is a widely used biological insecticide,which can form symbiotic relationships with plants via endophytic colonization, increasing plant biomass and the ability to resist biotic stress. An increase in the water absorption capacity and relative water content of tomato roots as well as the number, length, and width of tomato leaves stomata were observed after B. bassiana colonization via root irrigation. Meanwhile, peroxidase activity and proline content increased significantly, while malondialdehyde reduced significantly. Expression levels of key genes related to stomatal development, as well as drought tolerance pathways such as jasmonic acid, ascorbate peroxidase, redox homeostasis, nitrogen metabolism, carotenoid biosynthesis, and fatty acid biosynthesis also increased significantly. These results indicate that colonization of B. bassiana enhances the water absorption capacity of tomato seedlings as well as the rate of transpiration via increase the number and size of stomata and improved drought tolerance in tomato seedlings significantly and increases drought tolerance in tomato via the “water spender” pathway, which provide a new strategy for improving crop resistance to drought stress.