The growth–defense pivot: crisis management in plants mediated by LRR-RK surface receptors

• LRR-RKs are the largest receptor class in plants.
• Plant LRR-RKs have a unique activation mechanism.
• LRR-RKs are dual-specificity kinases.
• LRR-RKs signal through common and unique signaling components.

Plants must adapt to their environment and require mechanisms for sensing their surroundings and responding appropriately. An expanded family of more than 200 leucine-rich repeat (LRR) receptor kinases (LRR-RKs) transduces fluctuating and often contradictory signals from the environment into changes in nuclear gene expression. Two LRR-RKs, BRASSINOSTEROID INSENSITIVE 1 (BRI1), a steroid receptor, and FLAGELLIN SENSITIVE 2 (FLS2), an innate immune receptor that recognizes bacterial flagellin, act cooperatively to partition necessary growth–defense trade-offs. BRI1 and FLS2 share common signaling components and slightly different activation mechanisms. BRI1 and FLS2 are paradigms for understanding the signaling mechanisms of LRR-containing receptors in plants.