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Identification of host factors recruited by plant pathogens

Identification of host factors recruited by plant pathogens . Ester Buiate Physiology of Plant Health and Disease Instructor - Dr. Aardra Kachroo. What are host factors ?. Gene-for-gene hypothesis

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Identification of host factors recruited by plant pathogens

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  1. Identification of host factors recruited byplant pathogens Ester Buiate PhysiologyofPlantHealthandDisease Instructor - Dr. AardraKachroo

  2. What are host factors? • Gene-for-genehypothesis • For everyavirulence (Avr) gene in thepathogenthere is a resistance (R) gene in the host • Theinteractionbetweenthoseproteins leads to activationof host defense system, thatstopsthepathogengrowth

  3. Host factor

  4. Effectorprotein

  5. Theeffectorproteins • Avirulence genes encodedbypathogensthat cause infection • Effectorproteinscansuppress host defenseresponses(Nomuraet al.,2006)

  6. PAMPsandMAMPs • Provides a basal resistance • Pathogen-Associated Molecular Patterns • Chitin: fungalcellwalls • Flagellin: bacteria • PAMP RecognitionReceptors (PRRs) • Plant receptors that recognize PAMPs

  7. Resistancepathway Jones & Dangl, 2006 Nature

  8. How does effectors work? • Sctructural roles • Haustorialmatrix • Promotenutrientleakage to thepathogen • Supressresistanceresponse: • InhibitPAMPssignalingpathway • Celltraffcking

  9. Fungi

  10. Fungi Ustilagomaydis • Infectsmayzeandteosinte • Modelorganism Picture: TheAmericanPhytopathologicalSociety

  11. Type II Secretory System CanbeATP-dependent Talbot, Nature 2007

  12. Ustilagomaydisand Pep1 • Gene clusters upregulated during biotrophic development were mutated • None was essential for the initial development • Search for an effector gene that • Carry a secretion signal • Produced a novel protein Protein essential during prenetration 1

  13. Ustilagomaydisand Pep1 GFP RFP

  14. Ustilagomaydisand Pep1 SG200 Fungal hyphae inside plant SG200 pep1 Mutant was arrested

  15. Ustilagomaydisand Pep1 Insertion of RFP on citoplasm and GFP on Pep1 A- media culture B – penetration of maize epidermis C,D,E – intracellularly growth

  16. Ustilagomaydisand Pep1 • Pep1 does not affect saprophytic growth neither appressoria formation • Pep1 is essential for successful invasion of maize • Plant defense responses are downregulated after penetration • Pep1 is a pathogen effector absolutely required for the transition from saprophytic to biotrophic growth

  17. Ustilagomaydisand Pep1 • How Pep1 works? • Pep1 could active other effector proteins • Pep1 could interfere with plant signalling

  18. Virus

  19. TobaccoMosaicVirus • Infectstobacco, tomatoandothersolanaceous • Firstvirusdiscovered Picture: TheAmericanPhytopathologicalSociety

  20. TobaccoMosaicVirus • Are host dependent • Virus RNA are recognizedandinduce RNA interferencedefensepathways in the host Studyfocusedon TMV replicaseproteinand NAC domainprotein ATAF2, which is associatedwith host defenseresponsesandchanges in virusaccumulation

  21. TobaccoMosaicVirusdegradationof ATAF2 GFP expression with TMV

  22. TobaccoMosaicVirusdegradationof ATAF2 Reduction of ATAF2 levels

  23. TobaccoMosaicVirusdegradationof ATAF2 ATAF2 mRNA levels are high

  24. TobaccoMosaicVirusdegradationof ATAF2 Proteasome inhibitor increased ATAF2 level

  25. TobaccoMosaicVirus • Interactionbetweenpathogenreplicaseand host NAC protein ATAF2 • Low GFP in infectedtissues • Virus-directedproteindegradation Disrupt host defenses

  26. Bacteria

  27. Bacteria Pseudomonassyringae • Infects a wide range ofplantsandcrops • Modelorganism • Tomatobacterialspeck Picture: K. Loeffler and A. Collmer, Cornell University

  28. Type III secretion system • Proteinofbacteriathatinjectseffectorproteinsfromthepathogenintothe host cell Picture: Universityof Kansas, Dr. Tang

  29. Pseudomonassyringae • Mutation in aneffector gene (HopM1) • No symptoms, lowbacterialpopulation • PlantswithhopM1complementedthevirulencedefect • TheyfoundA. thalianaHopMinteractors(AtMIN) • AtMINencondes a proteinthat is crucial for vesicletrafficking system

  30. Pseudomonassyringae DC3000 – wild type ∆CEL – lacks HopM hrcC – secretion defective

  31. Pseudomonassyringae Inoculation with a trafficking inhibitor DC3000 – wild type ∆CEL – lacks HopM hrcC – secretion defective

  32. Bacteria • AtMIN encodes ARF GEF protein, that are crucial for vesicle trafficking system in eukaryotic cells • HopM1 probablyadapts to thatprotein, andtargets it to the host proteasome system Eliminating a component of vesicle traffic pathway is an effective strategy of avoiding the extracellular cell wall–associated host defense

  33. Conclusions • Understand effector proteins and their co-evolution with resistance genes • Howimmune system works • Newdisease management

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