Abstract
Plant productivity is severely constrained by diverse pathogens, among which oomycetes represent some of the most destructive threats to global agriculture. These filamentous microorganisms cause devastating diseases, including potato late blight and downy mildew, leading to significant yield losses in major crops. Successful infection relies on the formation of haustoria through which oomycetes deliver numerous effector proteins that manipulate host cellular processes and suppress both pattern-triggered and effector-triggered immunity. To date, three major classes of oomycete effectors, including RXLR, Crinkler, and CHXC, along with a putative class YxSL [RK], have been identified in oomycetes. These effector molecules, along with the recently identified apoplastic effectors, play key roles in governing compatible and incompatible interactions and establishing disease in the host plant. Plants perceive these effectors by deploying multilayered immune strategies including plasma-membrane localized pattern-recognition receptors (PRRs) and intracellular NLR receptors that induce redox- and hormone-regulated defense pathways, and dynamic remodeling of transcriptional and metabolic networks. Understanding these effectors and how they manipulate host defense is a prerequisite for the generation of disease-resistant plants. In this review, we discuss the recent progress in the oomycete effectors, their secretion system, and their targets in the plant cells. By integrating pathogen strategies with host immune responses, we highlight how effector-mediated manipulation of plant signaling provides new opportunities for breeding and engineering broad-spectrum and durable resistance against oomycete pathogens.
