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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

Identification of host factors recruited byplant pathogens

Ester Buiate


Instructor - Dr. AardraKachroo

what are host factors
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
the effector proteins
  • Avirulence genes encodedbypathogensthat cause infection
  • Effectorproteinscansuppress host defenseresponses(Nomuraet al.,2006)
pamps and mamps
  • Provides a basal resistance
  • Pathogen-Associated Molecular Patterns
    • Chitin: fungalcellwalls
    • Flagellin: bacteria
  • PAMP RecognitionReceptors (PRRs)
    • Plant receptors that recognize PAMPs
resistance pathway

Jones & Dangl, 2006 Nature

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


  • Infectsmayzeandteosinte
  • Modelorganism

Picture: TheAmericanPhytopathologicalSociety

type ii secretory system
Type II Secretory System


Talbot, Nature 2007

ustilago maydis and pep1
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

ustilago maydis and pep12
Ustilagomaydisand Pep1


Fungal hyphae inside plant

SG200 pep1

Mutant was arrested

ustilago maydis and pep13
Ustilagomaydisand Pep1

Insertion of RFP on citoplasm and GFP on Pep1

A- media culture B – penetration of maize epidermis C,D,E – intracellularly growth

ustilago maydis and pep14
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
ustilago maydis and pep15
Ustilagomaydisand Pep1
  • How Pep1 works?
    • Pep1 could active other effector proteins
    • Pep1 could interfere with plant signalling
tobacco mosaic virus
  • Infectstobacco, tomatoandothersolanaceous
  • Firstvirusdiscovered

Picture: TheAmericanPhytopathologicalSociety

tobacco mosaic virus1
  • 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

tobacco mosaic virus degradation of ataf21
TobaccoMosaicVirusdegradationof ATAF2

Reduction of ATAF2 levels

tobacco mosaic virus degradation of ataf22
TobaccoMosaicVirusdegradationof ATAF2

ATAF2 mRNA levels are high

tobacco mosaic virus degradation of ataf23
TobaccoMosaicVirusdegradationof ATAF2

Proteasome inhibitor increased ATAF2 level

tobacco mosaic virus2
  • Interactionbetweenpathogenreplicaseand host NAC protein ATAF2
    • Low GFP in infectedtissues
  • Virus-directedproteindegradation

Disrupt host defenses



  • Infects a wide range ofplantsandcrops
  • Modelorganism
  • Tomatobacterialspeck

Picture: K. Loeffler and A. Collmer, Cornell University

type iii secretion system
Type III secretion system
  • Proteinofbacteriathatinjectseffectorproteinsfromthepathogenintothe host cell

Picture: Universityof Kansas, Dr. Tang

pseudomonas syringae
  • Mutation in aneffector gene (HopM1)
    • No symptoms, lowbacterialpopulation
  • PlantswithhopM1complementedthevirulencedefect
  • TheyfoundA. thalianaHopMinteractors(AtMIN)
    • AtMINencondes a proteinthat is crucial for vesicletrafficking system
pseudomonas syringae1

DC3000 – wild type

∆CEL – lacks HopM

hrcC – secretion defective

pseudomonas syringae2

Inoculation with a trafficking inhibitor

DC3000 – wild type

∆CEL – lacks HopM

hrcC – secretion defective

  • 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

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