Plant-Pathogen Effectors: Cellular Probes Interfering with Plant Defenses in Spatial and Temporal Manners

Abstract

Plants possess large arsenals of immune receptors capable of recognizing all pathogen classes. To cause disease, pathogenic organisms must be able to overcome physical barriers, suppress or evade immune perception, and derive nutrients from host tissues. Consequently, to facilitate some of these processes, pathogens secrete effector proteins that promote colonization. This review covers recent advances in the field of effector biology, focusing on conserved cellular processes targeted by effectors from diverse pathogens. The ability of effectors to facilitate pathogen entry into the host interior, suppress plant immune perception, and alter host physiology for pathogen benefit is discussed. Pathogens also deploy effectors in a spatial and temporal manner, depending on infection stage. Recent advances have also enhanced our understanding of effectors acting in specific plant organs and tissues. Effectors are excellent cellular probes that facilitate insight into biological processes as well as key points of vulnerability in plant immune signaling networks.

Direct and Indirect Visualization of Bacterial Effector Delivery into Diverse Plant Cell Types during Infection

“…Pathogen effectors are virulence factors that suppress diverse aspects of plant immunity and thus can be excellent cellular probes for investigating plant innate immune responses (Toruño et al, 2016). Here, we developed the GFP strand system to facilitate investigation of effector delivery and function during natural infection.…”

“…An important aspect of pathogenicity is the delivery of pathogen proteins, termed effectors, into host cells (Toruño et al, 2016). Effectors can modulate host metabolism, shut down host defense signaling, and suppress cell death (Toruño et al, 2016).…”

“…An important aspect of pathogenicity is the delivery of pathogen proteins, termed effectors, into host cells (Toruño et al, 2016). Effectors can modulate host metabolism, shut down host defense signaling, and suppress cell death (Toruño et al, 2016). Gram-negative bacterial pathogens such as the foliar pathogen Pseudomonas syringae and the vascular pathogen Ralstonia solanacearum use the type III secretion system (TTSS), a proteinaceous needle-like structure, to directly deliver effectors inside host cells (Chang et al, 2014).…”

Identification of Rehmannia glutinosa L. NB-ARC family proteins and their typical changes under consecutive monoculture stress

“…Previous studies have revealed that the expression of pathogenic effectors is closely related to the stage and (Toruño et al 2016). For example, the specific effectors, C. higginsianum effectors, either inhibit or promote cell death after undergoing threefold increase of expression during infection of Colletotrichum higginsianum in Arabidopsis (Kleemann et al 2012).…”

Tracking the Bacterial Type III Secretion System: Visualization of Effector Delivery Using Split Fluorescent Proteins

“…These effectors have multiple, nefarious functions that help the pathogen thrive in its host (reviewed in Toruñ o et al, 2016). Effectors target conserved host processes including pathways for entry into the host (for example, regulation of stomatal aperture in plants, perception of pathogens, regulation of cell death, transcription, RNA interference, defensive proteases, and other enzymes such as chitinases).…”