The roles of ABA in plant-pathogen interactions.

Defence against abiotic and biotic stresses is crucial for the fitness and survival of plants under adverse or suboptimal growth conditions. The phytohormone abscisic acid (ABA) is not only important for mediating abiotic stress responses, but also plays a multifaceted and pivotal role in plant immunity. This review presents examples demonstrating the importance of crosstalk between ABA and the key biotic stress phytohormone salicylic acid in determining the outcome of plant--pathogen interactions. We then provide an overview of how ABA influences plant defence responses against various phytopathogens with particular emphasis on the Arabidopsis--Pseudomonas syringae model pathosystem. Lastly, we discuss future directions for studies of ABA in plant immunity with emphasis on, its role in the crosstalk between biotic and abiotic stress responses, the importance of distinguishing direct and indirect effects of ABA, as well as the prospect of utilizing the recently elucidated core ABA signaling network to gain further insights into the roles of ABA in plant immunity.