Self/nonself perception and recognition mechanisms in plants: a comparison of self‐incompatibility and innate immunity

Abstract

SummaryAnalyses of emerging concepts indicate that parallels exist between selfincompatibility and pathogen recognition. In the case of surveillance of 'nonself', plant immune responses are triggered either by pattern recognition receptors (PRRs) that detect conserved pathogen-associated molecular patterns (PAMPs) or by resistance (R) proteins recognizing isolate-specific pathogen effectors. PAMP detection is an important component of innate immunity in plants and serves as an early warning system for the presence of potential pathogens and activation of plant defense mechanisms. In the Brassicaceae, the recognition of 'self' and self-incompatibility are components of a receptor-ligand based mechanism that utilizes an S receptor kinase (SRK) to perceive and reject 'self'-pollen. SRK is an S-domain receptor-like kinase (RLK), which in turn is part of the RLK family, some members of which represent PRRs involved in the detection of PAMPs. S-domain RLKs also occur in species that do not exhibit self-incompatibility and are up-regulated in response to wounding, PAMPs and pathogen recognition. Although evolution may have driven expansion of certain RLK families to serve roles in particular physiological processes, this may not exclude these receptor types from functioning in different programs. Recent findings on self/nonself recognition are reviewed and conceptual and mechanistic links between microbial recognition and self-incompatibility are discussed. IntroductionThe two separate mechanisms of innate immunity and selfincompatibility (SI) are remarkably similar. The similarities and differences between the two mechanisms in terms of functions, functional outcomes, selective processes, responses, recognition molecules, recognition receptors, and signal transduction and perception are summarized herein. In order to elucidate how innate immunity fits into the global picture of overlapping and complex plant defense mechanisms, a short overview is presented first. In addition, an overview of SI is given to elucidate the molecular and biochemical mode of SI in the Brassicaceae. This is followed by a discussion of the role of receptor-like kinases (RLKs) in defense mechanisms and SI. While the role of S-domain RLKs in SI within the Brassicaceae is well described, the role of these receptors in pathogen perception and defense is not widely recognized.Plant innate immunity, with its associated defense mechanisms, exhibits similar characteristics to the mammalian and insect mechanisms (Nürnberger et al., 2004;Zipfel & Felix, 2005). Although they express an apparent passivity associated with their sedentary lifestyle, and are simultaneously exposed to evolving pathogens as well as environmental stresses, plants have evolved a unique metabolic plasticity that allows them to perceive pathogens and unleash effective defense strategies. The innate immune system in plants is unable to acquire or specifically adapt like the animal adaptive immune system (Goldsby et al., 2000) and relies on a spectrum of predetermined receptors ex...

Similarities between Reproductive and Immune Pistil Transcriptomes of Arabidopsis Species

“…It is already known that recognition mechanisms in self-incompatibility systems and host-pathogen interactions share common characteristics regarding their morphological, genetic, and signaling pathways (Sanabria et al, 2008;Dresselhaus and Márton, 2009). Pistils are an ideal experimental model in which to systematically investigate the genetic basis of these two processes and in which to identify candidate genes mediating intraspecific and interspecific pollen recognition.…”

“…Previously, it has been suggested that the response of the pistil to foreign or incompatible pollen might bear similarities with the reaction to fungal invasion (Sanabria et al, 2008;Dresselhaus and Márton, 2009). To test this hypothesis, we used different Arabidopsis species to study the relationship between the immune response and pollination-associated processes at the transcriptomic level.…”

Tackling Drought Stress: RECEPTOR-LIKE KINASES Present New Approaches

“…It has been shown in a number of studies that RLKs and their peptide ligands play key roles in regulating vegetative growth and development, protection against pathogens, and reproductive success in generating seeds and fruits and hindering premature abscission (Afzal et al, 2008;Sanabria et al, 2008;De Smet et al, 2009;Tör et al, 2009;Zhao et al, 2009;Aalen, 2011;BoissonDernier et al, 2011;Gish and Clark, 2011;Nodine et al, 2011;Butenko and Aalen, 2012). The overall picture that emerges from many different studies is one of a bewilderingly complex set of RLKs that may be specific to the level of individual cells.…”

A domain swap approach reveals a role of the plant wall-associated kinase 1 (WAK1) as a receptor of oligogalacturonides

“…Besides inducing defense responses, OGs also affect several aspects of plant growth and development (5,12). Like hyaluronan fragments, OGs are regarded as host-or damage-associated molecular patterns (HAMPs or DAMPs) and their biological activity is related to their molecular size because OGs with a degree of polymerization (DP) between 10 and 15 are the most active (13,14). Notably, the "egg box" conformation is necessary for the biological activity of OGs (5,15).…”