Homologous RXLR effectors from Hyaloperonospora arabidopsidis and Phytophthora sojae suppress immunity in distantly related plants.
ABSTRACT Diverse pathogens secrete effector proteins into plant cells to manipulate host cellular processes. Oomycete pathogens contain large complements of predicted effector genes defined by an RXLR host cell entry motif. The genome of Hyaloperonospora arabidopsidis (Hpa, downy mildew of Arabidopsis) contains at least 134 candidate RXLR effector genes. Only a small subset of these genes is conserved in related oomycetes from the Phytophthora genus. Here, we describe a comparative functional characterization of the Hpa RXLR effector gene HaRxL96 and a homologous gene, PsAvh163, from the soybean pathogen Phytophthora sojae. HaRxL96 and PsAvh163 are induced during early stages of infection and carry a functional RXLR motif that is sufficient for protein uptake into plant cells. Both effectors can suppress immune responses in soybean. HaRxL96 suppresses immunity in Nicotiana benthamiana, while PsAvh163 induces an HR-like cell death response in Nicotiana that is dependent on RAR1 and Hsp90.1. Transgenic Arabidopsis plants expressing HaRxL96 or PsAvh163 exhibit elevated susceptibility to virulent and avirulent Hpa as well as decreased callose deposition in response to non-pathogenic P. syringae. Both effectors interfere with defense marker gene induction, but do not affect salicylic acid biosynthesis. Together, these experiments demonstrate that evolutionarily conserved effectors from different oomycete species can suppress immunity in plant species that are divergent from the source pathogen's host. © 2012 The Authors. The Plant Journal © 2012 Blackwell Publishing Ltd.
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ABSTRACT: Plant growth and response to environmental cues are largely governed by phytohormones. The plant hormones ethylene, jasmonic acid, and salicylic acid (SA) play a central role in the regulation of plant immune responses. In addition, other plant hormones, such as auxins, abscisic acid (ABA), cytokinins, gibberellins, and brassinosteroids, that have been thoroughly described to regulate plant development and growth, have recently emerged as key regulators of plant immunity. Plant hormones interact in complex networks to balance the response to developmental and environmental cues and thus limiting defense-associated fitness costs. The molecular mechanisms that govern these hormonal networks are largely unknown. Moreover, hormone signaling pathways are targeted by pathogens to disturb and evade plant defense responses. In this review, we address novel insights on the regulatory roles of the ABA, SA, and auxin in plant resistance to pathogens and we describe the complex interactions among their signal transduction pathways. The strategies developed by pathogens to evade hormone-mediated defensive responses are also described. Based on these data we discuss how hormone signaling could be manipulated to improve the resistance of crops to pathogens.Frontiers in Plant Science 01/2013; 4:155.
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ABSTRACT: A wide diversity of pathogens and mutualists of plant and animal hosts, including oomycetes and fungi, produce effector proteins that enter the cytoplasm of host cells. A major question has been whether or not entry by these effectors can occur independently of the microbe or requires machinery provided by the microbe. Numerous publications have documented that oomycete RxLR effectors and fungal RxLR-like effectors can enter plant and animal cells independent of the microbe. A recent re-examination of whether the RxLR domain of oomycete RxLR effectors is sufficient for microbe-independent entry into host cells, concluded that the RxLR domains of P. infestans Avr3a and of P. sojae Avr1b alone are NOT sufficient to enable microbe-independent entry of proteins into host and non-host plant and animal cells. Here we present new, more detailed data that unambiguously demonstrate that the RxLR domain of Avr1b does show efficient and specific entry into soybean root cells, and also into wheat leaf cells, at levels well above background non-specific entry. We also summarize host cell entry experiments with a wide diversity of oomycete and fungal effectors with RxLR or RxLR-like motifs that have been independently carried out by the six different labs that co-authored this letter. Finally we discuss possible technical reasons why specific cell entry may have been not detected.Molecular Plant-Microbe Interactions 04/2013; · 4.31 Impact Factor