HAU16008-07-2 - Disease Resistance Lecture 7 Tuesday Flax...

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1 www.cas.vanderbilt.edu/ bioimages/species/lius.htm Disease Resistance Lecture 7, Tuesday, November 04, 2008 Flax flower www.cas.vanderbilt.edu/ bioimages/species/lius.htm Host Plant Defense Response against Pathogens Flax flower Core Concepts and Topics : Lifestyles of pathogenic fungi: (obligate or non-obligate) biotroph versus necrotroph Innate resistance, primary and secondary Compatibility and incompatibility in pathgen-plant interactions Plant lines and pathogen races Genetics of pathogenicity of a toxin-producing necrotroph Genetics of plant defense by phytoalexin production Genetics of plant lines and fungal races in R gene-mediated resistance H.H. Flor and the gene-for-gene hypothesis Dominance of avirulence Molecular basis of gene-for-gene systems Direct versus indirect R-gene-Avirulence-gene interactions R genes as part of a surveillance system Avr gene and R gene diversity Readings: BIT16008-21-3 deWit, P.J.G.M. (2007) Cellular and Molecular Life Sciences 64:2726-2732 BIT16008-21-4 Bittel, P., and Robatzek, S. (2007) Current Opinion in Plant Biology 10:335-341
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2 Propagule = the form of a pathogen that propagates the infection -- spores or vegetative cells of bacteria, oomycetes and fungi -- virus particle (virion) Compatible interaction = successful and productive infection resulting from contact of a propagule with a plant part (typically several orders of magnitude increase in pathogen numbers) For almost all combinations of pathogen genotype and plant genotype, the interaction is incompatible (even with repeated contact) (no or limited pathogen increase; the pathogen is not successful) PRODUCTIVE INFECTIONS ARISE ONLY FROM SPECIFIC COMBINATIONS OF PATHOGEN GENOTYPE AND PLANT GENOTYPE For incompatible reactions, the incompatibility may be passive or may result from innate defense (defense not necessarily the result of actual infection, and not involving recombinational events to produce new nucleotide sequences as occurs in animal antibody production) Incompatibility is the norm Compare Non-host resistance Genotypic resistance Pathogen infection types Necrotroph Biotroph (obligate or non-obligate) Plant resistance types Constitutive defense (physical barriers, life cycle timing) Primary or basal innate defense (based on recognition of MAMPs) Secondary or genotypic innate defense (based on recognition of elicitors through R gene product action) Pathogen race and plant line (or variety; genotypic resistance) In many examples of genotypic resistance, several races of pathogen and several plant lines have been identified by testing for compatibility and incompatibility Only certain combinations of race of pathogen and line of plant result in a compatible interaction (successful infection) Some basics Modified from Jones and Dangl 2006 Nature Reviews 444:323-328 Current notions about plant pathogen resistance systems PAMP- triggered immunity (PTI) Elicitor- triggered immunity (ETI) Amplitude of defense Pathogen recognition receptors (PRRs) Actions of pathogen effectors MAMP = microbe-associated molecular pattern (examples bacterial flagellin,
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