Ethylene: A Master Regulator of Plant–Microbe Interactions under Abiotic Stresses

The plant phytohormone ethylene regulates numerous physiological processes and contributes to plant–microbe interactions. Plants induce ethylene production to ward off pathogens after recognition of conserved microbe-associated molecular patterns (MAMPs). However, plant immune responses against pathogens are essentially not different from those triggered by neutral and beneficial microbes. Recent studies indicate that ethylene is an important factor for beneficial plant–microbial association under abiotic stress such as salt and heat stress. The association of beneficial microbes with plants under abiotic stresses modulates ethylene levels which control the expression of ethylene-responsive genes (ERF), and ERFs further regulate the plant transcriptome, epi-transcriptome, Na(+)/K(+) homeostasis and antioxidant defense mechanisms against reactive oxygen species (ROS). Understanding ethylene-dependent plant–microbe interactions is crucial for the development of new strategies aimed at enhancing plant tolerance to harsh environmental conditions. In this review, we underline the importance of ethylene in beneficial plant–microbe interaction under abiotic stresses.