systemic acquired resistance (sar) background on sar molecular changes associated with sar role of...
TRANSCRIPT
Systemic acquired resistance (SAR)
Background on SAR
Molecular changes associated with SAR
Role of SA and other signaling molecules
Role of NPR1 (non-expresser of pathogenesis related genes 1)
Roles of TGA and WRKY transcription factors
Role of chromatin remodeling in SAR
What do we know about SAR?
Systemic acquired resistance
Baker et al. 1997. Science. 276:726
Systemic acquired resistance
Systemic acquired resistance was first recognized as a significant phenomenon in the early 1900s.At that time, it was recognized that infection of plants with “necrotizing” pathogens (causing HR)often results in enhanced resistance to subsequent infections by a variety of fungal, bacterial andviral pathogens. This physiological immunity was termed systemic acquired resistance (SAR).
SAR confers a broad spectrum type of resistance
SAR is effective against some but not all pathogens:
Tobacco: Phytophthora parasitica, Cercospora nicotianae, Peronospora tabacinaTobacco mosaic virus, Tobacco necrosis virus,Pseudomonas syringae pv. tabaci, Erwinia carotovora
Not effective against: Botrytis cinerea or Alternaria alternata
Arabidopsis: Phytophthora parasitica Turnip crinkle virus Pseudomonas syringae pv. tomato DC3000
Systemic acquired resistance was associated with the coordinated induction of a set of SAR genesencoding proteins known as Pathogenesis-related (PR) proteins (Van Loon and Gianinazzi (early 1970s).
(1979) White found that acetyl salicylic acid application sufficient to induce PR gene expressionand enhanced resistance to tobacco mosaic virus in tobacco plant. Discovery came out theinterest in developing chemical control methods for viral infection. After that several groups wenton to show that salicylic acid application on tobacco leaves mimics pathogen induced expressionof PR genes and pathogen resistance in treated tissues.
(1990) Two groups one led by Klessig and Raskin and another led by Metrauxfound that salicylic acid accumulates in cucumber and tobacco plants prior to pathogen infection, butbefore the onset of resistance.
The work by these and many others led to the hypothesis that salicylic acid (SA) is the endogenoussignal molecule that is required for the induction of systemic acquired resistance.
(1993/1994) The group headed by Ryals made tobacco plants that could not accumulate SA and found that these plants were defective in their ability to develop systemic acquired resistance.This work demonstrated a central role for SA in establishing systemic acquired resistance.The group also demonstrated that these tobacco plants were defective in their ability to accumulate PR proteins.
(1997) Cloning of NPR1, a key regulator of SAR
Some key events in understanding regulation of SAR
PR (Pathogenesis-Related) proteins
Proteins secreted predominantly into intercellular spaces in response to wounding or infection.
Soluble at pH 3
Basic homologs also found (in vacuole).
Proteinase resistant (but not proteinase inhibitors).
Some are developmentally expressed as part of normal plant development in absence of wound or
infection (e.g. flowering).
PR proteins first identified as major proteins induced by necrotizing pathogens(pathogens that induced the hypersensitive response)
Acidic gel Basic gel
All tobaccoPR proteins
PR proteins
Proteins first isolatedfrom apoplast ofTMV-infected tobacco.
Induced by many other pathogens.
Some PR proteins are also induced byabiotic stresses.
Traditional PR protein gels
old
nom
en
clatu
re
PR genes induced after HR or SA treatment
What do PR proteins do?
Sels et al. (2008) Plant Physiol. Biochem. 46:941-950Also van Loon et al. (2006) Annu. Rev. Phytopathol. 44:135-162
Some are members of large gene families – e.g. PR-1
van Loon et al. (2006) Annu. Rev. Phytopathol. 44:135-162
Constitutive expression of chitinase PR protein confersresistance to Rhizoctonia solani
Brogue et al. (1991) Science 254, 1194-1196
Control Line 373
230238329373
548
18 days after growth in R. solani-laden sand 11 d.a.g. in R. solani sand
Application of salicylic acid mimics SAR
(1979) White found that the application of aspirin, salicylic acid, and benzoic acid resulted in enhanced resistance to TMV. Used 3 tobacco cultivars that contained the N resistance gene that confers HR to TMV. Found > 90% reduction in lesion number in treated leaves versus water control.
Lesi
ons
obta
ined a
fter
seco
nd inocu
lati
on
SA
SA accumulation is associated with acquisition of resistance
Science (1993) 261, 754-756.
Central role of SA in SAR
PR-1
PR-2
PR-3
PR-1 mRNA
Central role for SA in defense continued
Enhanced susceptibility
Loss of resistance
INA induces resistancein presence of nahG
Mobile inducers of SAR
Kachroo. 2013. Curr. Opin. Plant Biol. 16:527
What is the mobile systemic signal(s) for SAR?
Methylsalicylate – meSA
SABP2 (meSA esterase) is required for SAR
Park et al. Science 318:113-116
What is the mobile systemic signal(s) for SAR?
Methylsalicylate – meSA
SAMT1 (SA methyltransferase) is required for SAR
Park et al. Science 318:113-116
What is the mobile systemic signal(s) for SAR?
Methylsalicylate – meSA
meSA induces SAR in systemic tissues expressing SABP2 (MeSA esterase)
Park et al. Science 318:113-116
A role of glycerol-3-phosphate in SAR
Reduced SAR in gly1 and gli1 mutants G3P levels increase in response to pathogenin local and systemic tissues
Chanda et al. (2011) Nat. Genet. 43:421-427
Exogenous G3P restores SAR in gli1 and gly1 plants
A role of glycerol-3-phosphate in SAR
Chanda et al. (2011) Nat. Genet. 43:421-427
G3P conferred SAR is dependent on DIR1DIR1 is a proposed lipid transporter protein
Chanda et al. (2011) Nat. Genet. 43:421-427
DIR1 is needed for G3P transport
Azeleic acid
Model for azeleic acid induced systemic acquired resistance
Yu et al. 2013. Cell Rep. 3:1266
Abietaine diterpenoid dehydroabietinal (DA)
Chaturvedi et al. 2012. Plant J. 71:161
Signaling steps between SA and PR protein expressionand disease resistance.
The Arabidopsis NPR1 Gene That ControlsSystemic Acquired Resistance Encodesa Novel Protein Containing Ankyrin RepeatsHui Cao, Jane Glazebrook, Joseph D. Clarke, Sigrid Volko, and Xinnian Dong (1997) Cell 88, 57–63,
Previously: Linked a PR protein promoter called BGL2 to GUS.
Screened thousands of mutant transgenic BGL2-GUS plants forABSENCE of GUS activity induced by SA treatment.
Using standard Arabidopsis genetic mapping methods, identified asingle mutant gene, npr1. Phenotype: Complete absence of GUS activity in response to SA Absence of PR-1, PR-5, BGL2 expression in response to SA Is now susceptible to Peronospora parasitica and to Pseudomonas syringae pv maculicola (Psm).
Cao et al. (1997) Cell 88, 57–63,
Cloned NPR1 by standard 1990’s methods. Chromosome walking, YAC library…
Proof of cloning by transgenic comple-mentation of mutants w/ wildtype NPR1.
wt
none non-compl. NPR1
npr1-2
NPR1
genotype:
transgene:none
wt npr1-1 npr1-1 + NPR1
Psm
inocu
late
d
GU
Ssy
mpto
ms
Cao et al. (1997) Cell 88, 57–63,
Cao et al. (1997) Cell 88, 57–63,
NPR1 has ankyrin repeats
Ankyrin repeats arein lots of differentproteins.
Involved in protein-protein interactions.Especially in proteinsthat control trans-cription.
In NF-kB and I-kB inmammals. Inducedby many pathogens,stresses…
NPR1 is reduced to a monomer during plant defense
Mou et al., (2003) Cell, 113:935–944
Expression of PR-1 is associated with NPR1 monomerization
Mou et al., (2003) Cell, 113:935–944
Monomeric NPR1 localizes to the nucleus
Mou et al., (2003) Cell, 113:935–944
Zhou et al. (2000) MPMI 13:191–202
NPR1 interacts with TGA transcription factors in yeast two-hybrid assays
TGA transcription factors bind to TGACG sequences found in the promoter of genessuch as PR-1
NPR1 enhances TGA1 binding to the as-1 element underreducing conditions
Despres et al. (2003) Plant Cell. 15:2181–2191,
Recognize the motif: (T)(T)TGAC(C/T).Have the conserved WRKYGQK at N-terminal end.Have a novel zinc-finger-like motif.Bind DNA via divalent cation (probably zinc).Approx. 100 members of WRKY family in Arabidopsis.NPR1 has 3 WRKY motifs in its promoter:
TTGACTTGACTTGGCTCTGCTCGTCAA
WRKY transcription factors: another key group of transcriptionfactors that regulate plant defense responses
The WRKY superfamily of plant transcription factorsThomas Eulgem, Paul J. Rushton, Silke Robatzek and Imre E. Somssich(2000) Trends Plant Sci 5, 199-205.
Conserved amino acidsin WRKY proteins ofArabidopsis (red).
Putative Zn-finger ligandsare highlighted in black.
Eulgem et al. (2000) TIPS 5, 199-205.
Wang et al. (2006) PLoS Pathogens 2:1042-1050
Identification of direct transcriptional targets of NPR1
WRKY54, WRKY38, WRKY59, WRKY18, WRKY70, WRKY66, and WRKY53 are induced directly by NPR1.
Evidence that WRKY58 negatively regulates plant defense
Wang et al. (2006) PLoS Pathogens 2:1042-1050
WRKY70 and 54 negativelyregulate SA biosynthesis andpositively regulate SAR
Wang et al. (2006) PLoS Pathogens 2:1042-1050
Identification and Cloning of a Negative Regulatorof Systemic Acquired Resistance, SNI1,through a Screen for Suppressors of npr1-1Xin Li, Yuelin Zhang, Joseph D. Clarke, Yan Li,†and Xinnian Dong* Cell, 98, 329–339, 1999.
Screened for EMS mutants of npr1-1 plants containing BGL2-GUSreporter.Look for plants that turn blue in response to INA (SA analog) like NPR1 wild type plants. But which, of course still harbor the npr1-1 mutation.Found 11 loci that gave increased GUS, out of 7000 plants screened.
Li et al., Cell 98, 329–339.
Li et al., Cell 98, 329–339.
Li et al., Cell 98, 329–339.
SNI1 is similar to mouse Retinoblastoma (Rb). Rb is a tumor suppressor that represses function of E2F transcription factor
Li et al., Cell 98, 329–339.
93-95% of genes upregulated in sni1 mutants are induced by BTH
SNI1 represses transcription in yeast
Mosher et al. (2006) Plant Cell, 18:1750–1765
sni1 mutation alters gene expression – most genes also induced by BTH
Chromatin modifications at the PR-1 promoter in sni1 mutants
Mosher et al. (2006) Plant Cell, 18:1750–1765
Model for signal transduction in SAR
Fu. 2013. Annu. Rev. Plant Biol. 64:839