Abstract
A first line of defense against pathogen attack for both plants and animals involves the detection of microbe-associated molecular patterns (MAMPs), followed by the induction of a complex immune response. Plants, like animals, encode several receptors that recognize different MAMPs. While these receptors are thought to function largely redundantly, the physiological responses to different MAMPs can differ in detail. Responses to MAMP exposure evolve quantitatively in natural populations of Arabidopsis thaliana, perhaps in response to environment specific differences in microbial threat. Here, we sought to determine the extent to which the detection of two canonical MAMPs were evolving redundantly or distinctly within natural populations. Our results reveal negligible correlation in plant growth responses between the bacterial MAMPs EF-Tu and flagellin. Further investigation of the genetic bases of differences in seedling growth inhibition and validation of 11 candidate genes reveal substantial differences in the genetic loci that underlie variation in response to these two MAMPs. Our results indicate that natural variation in MAMP recognition is largely MAMP-specific, indicating an ability to differentially tailor responses to EF-Tu and flagellin in A. thaliana populations.
Highlights
Pathogens pose a constant threat to their hosts
We sought to determine whether plants evolve distinct or shared responses to two canonical microbe associated molecular patterns (MAMPs) within natural populations
We comprehensively tested the extent of functional redundancy in the response of 186 genotypes of Arabidopsis thaliana to variants of each of two classes of bacterial signals, flagellin and elongation factor Tu (EF-Tu)
Summary
While lacking the adaptive immune system present in mammals, plants have evolved a two-tiered immune system of considerable specificity. The first tier of defense involves the recognition of microbe associated molecular patterns (MAMPs) that are common to many microbes. Plants recognize MAMPs, such as the elongation factor Tu (EF-Tu) and flagellin, or their epitopes elf and flg, by specialized receptors that allow the plant to discriminate self versus non-self and induce signaling cascades that result in defense responses [1, 2]. The second tier of the plant immune system involves the recognition of specific microbial strains (in contrast to semi-universal microbial patterns) via the activity of resistance proteins. The specificity of the immune system in distinguishing specific microbes was previously thought to lie primarily in the activity of resistance proteins. Recent studies have challenged this paradigm in demonstrating both qualitative and quantitative variation in MAMP perception [3]
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