Suppression of Plant Resistance Gene-Based Immunity by a Fungal Effector

Abstract

The innate immune system of plants consists of two layers. The first layer, called basal resistance, governs recognition of conserved microbial molecules and fends off most attempted invasions. The second layer is based on Resistance (R) genes that mediate recognition of effectors, proteins secreted by pathogens to suppress or evade basal resistance. Here, we show that a plant-pathogenic fungus secretes an effector that can both trigger and suppress R gene-based immunity. This effector, Avr1, is secreted by the xylem-invading fungus Fusarium oxysporum f.sp. lycopersici (Fol) and triggers disease resistance when the host plant, tomato, carries a matching R gene (I or I-1). At the same time, Avr1 suppresses the protective effect of two other R genes, I-2 and I-3. Based on these observations, we tentatively reconstruct the evolutionary arms race that has taken place between tomato R genes and effectors of Fol. This molecular analysis has revealed a hitherto unpredicted strategy for durable disease control based on resistance gene combinations.

Leaf endophytes and Populus genotype affect severity of damage from the necrotrophic leaf pathogen, Drepanopeziza populi

“…The idea of plant symbionts as ''vaccines'' was first suggested long ago (Beauv- v www.esajournals.org erie 1901), and is now referred to as systemic acquired resistance (SAR) or induced systemic resistance (ISR; Van Wees et al 2008). This mechanism could also potentially work in the opposite direction: leaf endophytes could increase disease severity by suppressing plant genetic resistance (Houterman et al 2008). Similarly, systemic acquired susceptibility (SAS) to one pathogen can be caused by prior infection by another pathogen (Bonello et al 2008).…”

Multiple Avirulence Loci and Allele-Specific Effector Recognition Control thePm3Race-Specific Resistance of Wheat to Powdery Mildew

“…Further evidence for genetic interactions that go beyond the simple gene-for-gene model was found in the interaction of Fusarium oxysporum with the I resistance genes in tomato. The Avr1 effector induces resistance in the presence of the I-1 gene but suppresses the resistance function of the I-2 and I-3 resistance genes (Houterman et al, 2008). In the same pathosystem, two additional specific suppressors of I gene function were identified in the pathogen, indicating the requirement of two fungal genes for immunity conferred by one resistance gene (Gawehns et al, 2014;Ma et al, 2015).…”

Analysis of Two in Planta Expressed LysM Effector Homologs from the FungusMycosphaerella graminicolaReveals Novel Functional Properties and Varying Contributions to Virulence on Wheat

“…This has led to plants evolving disease resistance proteins able to detect perturbations to virulence targets that then activate a second line of defense described as effector-triggered immunity (ETI; Boller and He, 2009). This subsequent level of immunity can itself be suppressed through pathogen effector functions (Houterman et al, 2008), giving rise to the "zigzag" model for interactions of plant pathogens with the plant defense machinery (Jones and Dangl, 2006). ETI frequently conforms to a gene-for gene model (Flor, 1971) whereby single genes/loci in the pathogen interact with single dominant genes/loci in the plant, giving rise to immunity.…”