Salicylic Acid Steers the Growth–Immunity Tradeoff

Plants possess an effective immune system to combat most microbial attackers. The activation of immune responses to biotrophic pathogens requires the hormone salicylic acid (SA). Accumulation of SA triggers a plethora of immune responses (like massive transcriptional reprogramming, cell wall strengthening, and production of secondary metabolites and antimicrobial proteins). A tradeoff of strong immune responses is the active suppression of plant growth and development. The tradeoff also works the opposite way, where active growth and developmental processes suppress SA production and immune responses. Here, we review research on the role of SA in the growth–immunity tradeoff and examples of how the tradeoff can be bypassed. This knowledge will be instrumental in resistance breeding of crops with optimal growth and effective immunity. The phytohormone salicylic acid (SA) stimulates plant immune responses to a broad range of plant pathogens.SA-induced immune responses contribute to the growth–immunity tradeoff: immune responses actively suppress growth and development and also the other way around, growth and developmental processes can suppress immunity.Immune signaling and growth-related processes directly affect SA biosynthesis and metabolism, to allow for a robust but transient immune response, after which growth and developmental processes are reactivatedThe growth–immunity tradeoff can be uncoupled by modifying signaling pathways downstream of SA.Bypassing the antagonism of SA on growth is a desirable trait for resistance breeding in crops, as this bypass can allow for sustainable resistance without yield losses.