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Plant Defense: A Glimpse. By Wisuwat Songnuan. Outline. Background Systemic Acquired Resistance NPR1-TGAs That’s not all… Future. Background. Background Outline. Why study plant resistance? Pathogen Recognition Gene-for-gene interactions Hypersensitive Response (HR)

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plant defense a glimpse

Plant Defense: A Glimpse

By

Wisuwat Songnuan

outline
Outline
  • Background
  • Systemic Acquired Resistance
  • NPR1-TGAs
  • That’s not all…
  • Future
background outline
Background Outline

Why study plant resistance?

Pathogen Recognition

Gene-for-gene interactions

Hypersensitive Response (HR)

Systemic Acquired Resistance (SAR)

why study plant resistance
Why study plant resistance?
  • 80% of total calories consumed by human population come from only six crops: wheat, rice, maize, potatoes, sweet potatoes, and manioc (Raven, P.H. et al, 1999).
  • We lose 12% of total crop yields to pathogen infection– equivalent to nine hundred million tons worldwide annually (Krimsky S. and Wrubel R., 1996).
plants under attack
Plants under attack
  • Microorganisms: viruses, bacteria, fungi
  • Nematodes
  • Insects & a few others
  • Us?
what will you do
What will YOU do?
  • Lots of enemies, attacking from all sides
  • Huge body
  • Cannot escape
  • No “patrol”
  • (no NIH grant)
how they do it
How THEY do it
  • Right after plants are dead, they are rotten
  • No wasting energy for ‘just in case’ immunity
  • All through “signaling”
pathogen recognition
Pathogen recognition
  • Gene-for-gene hypothesis: Upon infection by a particular avirulent pathogen, a corresponding R gene recognizes the avr product and triggers the defense mechanism.
    • Why do pathogens still possess avr genes?
  • Non-host resistance: Resistance of all members of a host species against all members of pathogen species
resistance r genes
Resistance (R) Genes
  • Dominant
  • Many ID so far
  • 5 classes recognized
    • NBS: Nucleotide binding site
    • Leucine-zipper and leucine-rich repeat (LRR)
    • Toll/IL-1R (TIR)
    • Protein kinase (PK), receptor-like kinase (RLKs)
the popular ones
The popular ones…
  • Maize Hm1 (1992): toxin reductase
  • Tomato Pto (1993): Ser/Thr kinase
  • Arabidopsis RPS2:
  • Tobacco N:
  • Tomato Cf9
  • Flax L6
  • Rice Xa21
hypersensitive response hr
Hypersensitive Response (HR)
  • Burst of oxygen reactive species around infection site
  • Synthesis of antimicrobial phytoalexins
  • Accumulation of Salicylic Acid (SA)
  • Directly kill and damage pathogens
  • Strengthen cell walls, and triggers apoptosis
  • Restrict pathogen from spreading
  • Rapid and local
systemic acquire resistance sar
Systemic Acquire Resistance (SAR)
  • Secondary response
  • Systemic
  • Broad-range resistance
  • Leads to Pathogenesis-Related (PR) gene expression
  • Signals: SA, JA, ethylene
salicylic acid sa

COOH

OH

Salicylic Acid (SA)
  • Accumulates in both local and systemic tissues (not the systemic signal)
  • Removal of SA (as in nahG plants) prevents induction of SAR
  • Analogs: INA or BTH
mutants affecting sa synthesis
Mutants affecting SA synthesis
  • Elevated SA accumulation
    • dnd1 (defense, no death 1): increased SA, but reduced HR, DND1 gene encodes cyclic-nucleotide-gated ion channel
    • mpk4: constitutive SA accumulation
    • edr1 (enhanced disease resistance 1): defective MAPKKK
mutants affecting sa synthesis17
Mutants affecting SA synthesis
  • reduced SA accumulation
    • eds1 (enhanced disease susceptibility 1): lipase homolog
    • pad4 (phytoalexin deficient 4): another lipase homolog
    • sid1 and sid2 (salicylic acid induction-deficient): defects in chorismate pathway
mutant screen
Mutant Screen
  • Aimed at identifying regulatory genes of SAR
  • Strategy: Transform Arabidopsis with GUS reporter driven by SA- and INA-responsive promotor from BGL2 gene
    • npr1 (non-expresser of PR genes) mutant: reduced induction of reporter gene with or without SA, INA
    • cpr (constitutive expresser of PR genes) mutants: constitutively express reporter genes
npr1 non expresser of pr genes
NPR1: non-expresser of PR genes
  • Also known as NIM1 or SAI1
  • Positive regulator of SAR
  • Downstream of SA, upstream of PR genes
  • npr1 mutants are susceptible to various pathogens
  • Overexpression of NPR1 generates broad-spectrum resistance
  • Unique, but similar to Iκ-B (negative regulator of immunity in animals)
pathogen related pr genes
Pathogen-Related (PR) Genes
  • Antimicrobial properties
  • Many identified
  • Categorized according to activity
  • Examples
    • PR-2 : beta-1,3-glucanase
    • PR-3 : chitinase
    • PR-12: defensin
slide22
SAR

Avr

R gene

SA

NPR1

PR-1 PR-2 PR-5

SAR

structural features of npr1
Structural features of NPR1

npr 1-2

nim 1-2

npr 1-1

NLS

  • 593 amino acids, 67 kD
  • Two protein-protein interaction domains: BTB/POZ and Ankyrin repeats
  • Contains NLS
  • Multiple phosphorylation sites
  • No DNA binding domain

S S

BTB

ARD

tga factors
TGA Factors
  • Found to interact with NPR1 through yeast-two hybrid
  • bZIP transcription factors
  • Six members in Arabidopsis (TGA1-6)
  • Might be redundant
  • Bind to as-1 element
npr1 tga2 interaction
NPR1-TGA2 interaction
  • Direct visualisation
slide38
SAR

Avr

R gene

SA

TGA2

NPR1

PR-1 PR-2 PR-5

SAR

yeast two hybrid
Yeast-two hybrid

Figure 1 a-d

tga2 mrna accumulation
TGA2 mRNA accumulation

untreated

P.parasitica

INA

Figure 2

tga5 mrna accumulation

untreated

P.parasitica

INA

TGA5 mRNA accumulation

Figure 3a

slide50
SAR

Avr

R gene

SA

TGA2

NPR1

TGA5

PR-1 PR-2 PR-5

SAR independent

resistance

SAR

a few others
A few others
  • Ethylene-mediated response
  • Jasmonic acid-mediated response
  • Induced systemic resistance (ISR)
  • MAPK cascades
the future
The future
  • Still a lot to learn
  • 2010 project
  • The golden era