过往文献抗逆抗病抗虫salicylates

Salicylates:

Defense

and

MoreSalicylates

–

plant

hormones

andpainkillersSalicylic

Acid

Acetylsalicylic

AcidASPIRINPhoto

credits:

Geaugagrrl;

Sten

PorNamed

forwhite

willowSalix

albaNamed

forSpiraea,

theformername

formeadowsweetHow

does

aspirin

work

in

people?Image

courtesy

cytochrome

c,

artfavorProtection

fromheart

attacks,strokes

andmaybe

cancer!ProstaglandinsPainFeverInflammationDecreasedplateletProstaglandins

are

afamily

of

lipid-derivedadhesionsignaling

moleculeswith

diverse

effectsCyclo-oxygenaseIts

main

effect

isto

limitprostaglandinproductionSalicylic

acid

is

used

to

treat

viralwarts,

e

and

sun-damaged

skinHigh

concentrationsof

SA

are

used

-

theeffect

is

mainly

dueto

removing

the

outerlayers

of

skinBefore

SAAfter

SAHow

do

salicylates

work

in

plants?SA’s

effects

in

plants

andanimals

are

unrelated

–plants

do

not

makeprostaglandins

and

theirepidermis

is

very

differentExpression

ofpathogen-induced

genesIncreasedsynthesis

of

SASignal

(e.g.Pathogen,

UV

light,developmental

cues)DEFENSEStress

responsesDevelopmentalresponsesIn

plants

SA’s

main

effect

is

to

alter

patterns

of

gene

expresMicroorganisms

are(hemi)biotrophic

or

necrotrophicCell

deathpanies

orprecedescolonization

bynecrotrophsBiotrophs

or

hemibiotrophscan

live

within

their

hosttissue

without

causing(immediate)

deathToxinPseudomonassyringae

inintercellular

spaceBestwick,

C.S.,

Brown,

I.R.,Bennett,M.,

and

Mansfield,

J.W.(1997).

Localizationof

hydrogen

peroxide

accumulation

during

the

hypersensitive

reaction

otoPseudomonassyringae

pvphaseolicola.

Plant

Cell

9:

209-221.Salicylates

participate

in

plantdefenses

to

biotrophic

pathogensTo

a

first

approximation,insectsand

necrotrophstrigger

jasmonateproduction,

andbiotrophs

triggersalicylate

productionJasmonatesSalicylatesTranscriptionalresponsesHistory

of

salicylate

researchNational

Library

ofMedicine;Raskin,

I.

(1992).

Salicylate,anew

planthormone.Plant

Physiol.

99Hippocrateswrote

about

theuse

of

willow

torelieve

pain

~2400

years

agoIn

1979

Whiteshowed

that

pre-treatment

of

a

leafwith

aspirin

or

SAconferredresistance

totobaccomosaicvirus

(TMV)In

1987endogenousSA

was

shown

to

beresponsiblefor

heatproduction

inArum

lilyflowersIn

1990

SA

wasshown

to

be

anendogenoussignal

in

defenseresponsesUntreatedsideSAtreatedCao,

H.,

Bowling,

S.A.,

Gordon,

A.S.,

and

Dong,

X.

(1994).

Characterization

ofanArabidopsismutantthat

is

nonresponsive

to

inducers

of

systemic

acquired

re

1592.

Rusterucci,

C.,

Aviv,

D.H.,

Holt,

B.F.,

III,

Dangl,

J.L.,

and

Parker,

J.E.

(2001).

The

disease

resistance

signaling

components

EDS1

and

PAD4

are

essenti

pathway

controlled

by

LSD1

in

Arabidopsis.

Plant

Cell

13:

2211-2224.

Delaney,

T.P.,

Uknes,

S.,

Vernooij,

B.,

Friedrich,

L.,

Weymann,

K.,

Negrotto,

D.,

Gaffne

Kessmann,

H.,

Ward,

E.

and

Ryals,

J.

(1994).

A

central

role

of

salicylic

acid

in

plant

disease

resistance.

Science.

266:

1247-1250

reprinted

with

permission

o

S.,

Knauf-Beiter,

G.,

Hengy,

G.,

Beckhove,

U.,

Kogel,

K.H.,

Oostendorp,

M.,

Staub,

T.,

Ward,

E.,

Kessmann,

H.,

and

Ryals,

J.

(1996).

Benzothiadiazole,

a

novel

systemic

acquired

resistance,

activates

gene

expression

and

disease

resistance

in

wheat.

Plant

Cell

8:

629-643.Tools

to

study

SA

and

disease

inplantsPathogengrowth

rateSA

analoguesPR-1

expression

(days

after

infection)Trypan

blue

stainsfungalstructures

within

the

plant

tissueand

dead

or

damaged

plant

cells.SA

treatment

slowspathogen

growthPathogen

infection

or

SA

treatmentinduces

PATHOGENESIS-RELATED

GENE1

(PR-1)

expressionFrom

Delaney,

T.P.,

Uknes,

S.,

Vernooij,

B.,

Friedrich,

L.,

Weymann,

K.,

Negrotto,

D.,

Gaffney,

T.,

Gut-Rella,

M.,

Kessmann,

H.,

Ward,

E.

and

Ryals,

J.

(199central

role

of

salicylic

acid

in

plant

disease

resistance.

Science.

266:

1247-1250,

reprinted

with

permission

from

AAAS.Before

SA-deficientplants

were

identifiedgenetically,

NahGexpression

was

used

toinvestigate

SA’s

roles.ControlNahG-expressingplantSalicylatehydroxylaseencoded

byNahGSAcatecholAlthough

it

is

very

effective,

concerns

abits

specificity

and

effects

of

catechol

meresearchers

now

prefer

other

methodsThe

bacterial

enzyme

encoded

byNahG

hydrolyzes

SA

to

catecholA

biosensor

that

emits

light

in

thepresence

of

SA

has

been

developedSeeHuang,W.E.,Huang,

L.,

Preston,G.M.,

Naylor,M.,Carr,

J.P.,

Li,

A.,

Singer,

A.C.,

Whitely,A.S.and

Wang,H.(2006)

Quantitativassay

of

salicylic

acid

in

tobacco

leaves

using

a

genetically

modified

biosensor

strain

of

Acinetobacter

sp.

ADP1.

Plant

J.

46:

1073-luxCDABEluxCDABEsalAsalANo

SA

=Nolight

emittedSA

=

LightemittedAn

SA-inducible

promoteris

fused

to

the

luxCDABEoperon,

which

producesluciferase

and

does

notrequire

exogenously-added

substrate.When

SA

is

present,

theoperon

is

expressed

andlight

is

producedLecture

outline

Synthesis,

conjugation

andtransportPerception

and

signaling

Salicylates

in

whole-plantprocesses•Image

credit:

Prof.

Dr.

Otto

Wilhelm

Thomé

Flora

von

Deutschland,

Österreich

undderSchweiz

1885,

Gera,

GerSynthesis,

conjugation

andtransportReprinted

with

permission

from

Chen,

Z.,Zheng,

Z.,

Huang,

J.,

Lai,

Z.

and

Fan,B.

(2009).

Biosynthesis

of

salicylic

acid

in

plants.

Plant

Signaling

&

Behavior.

4:also

Reprinted

from

Métraux,

J.-P.

(2002).

Recent

breakthroughs

in

the

study

of

salicylic

acid

biosynthesis.

Trends

in

Plant

Science

7:

332-334

withpermission

fA

small

amount

ofSA

is

derived

fromcinnamicacidproduced

by

PALin

the

cytoplasmCytoplasmca.

5%

totalChloroplastca.

95%

totalThere

aretwo

pathways

for

SAsynthesis,

via

ICS

and

PALPALICSThe

major

route

forthe

biosynthesis

ofSA

(up

to

95%

oftotal)

takes

place

inthe

chloroplast.

Oneof

the

key

enzymesis

ICS,

isochorismatesynthaseIn

the

top

experiment,

-Erysiphe

on

the

left

is

without

pathogen,

+Erysiphe

on

the

right

is

with

pathogen.

The

experiment

was

done

in

triplicateand

shows

results

fromeach

independent

experiment

three

separate

lanes.On

the

lower

panel,

hpi

is

hours

post

infection.

Expresison

of

two

genes,

ICS1

(biosynthesis

of

SA)

and

PR1

(response

to

SA)

are

shown

assolid

and

white

barsrespectively.In

many

plants

ICS1

is

upregulatedby

pathogen

exposureExpression

of

ICS1increases

uponexposure

to

a

pathogenICS1

PR1PR1

is

an

SA-inducedpathogenresponsive

geneReprinted

by

permission

from

MacmillanPublishersLtd.

Wildermuth,

M.C.,

Dewdney,

J.,

Wu,

G.,

and

Ausubel,

F.M.(2001).Isochorismate

synthis

required

to

synthesize

salicylic

acid

for

plant

defence.

Nature

414:

562-565

copyright

2001.The

leaves

on

the

right

are

stained

withtrypan

blue,

revealing

muchmore

pathogen

growth

in

the

sid2

SA-deficient

mutant.Mutants

in

ICS1

are

blocked

in

SAsynthesis

and

susceptible

to

diseaseNawrath,

C.

and

Metraux,

J.-P.

(1999).

Salicylic

acid

induction–deficient

mutants

of

Arabidopsis

express

PR-2

and

PR-5

and

accumulate

high

levelcamalexin

after

pathogen

inoculation.

Plant

Cell.

11:

1393-1404.Col-0Reduced

accumulation

of

freeand

conjugated

SAsid2

and

eds16

areICS1

mutantssid2Increased

growth

ofHyaloperonosporaarabidopsidispathogenSA

synthesis

is

controlled

bypositive

and

negative

factorsTranscription

factorsthat

specificallyactivate

or

repressICS1

expression

havebeen

identifiedPathogen

infection,

UVlight,

ozone

and

abioticstresses

promote

SAaccumulationSharma,

Y.K.,

León,

J.,

Raskin,

I.,

and

Davis,K.R.(1996).

Ozone-induced

responses

in

Arabidopsis

thaliana:the

role

of

salicylic

acid

in

theaccumulation

otranscripts

and

induced

resistance.

Proc.

Natl.

Acad.

Sci.

USA

93:

5099-5104,

copyright

1996,

National

Academy

of

Sciences

USA.OzonetreatmentSA

is

modified

and

conjugated

toactive

and

inactive

compoundsUsed

with

permission

from

Vlot,

A.C.,

Dempsey,

D.M.A.,

and

Klessig,

D.F.

(2009).

Salicylic

acid,

a

multifaceted

horm

combat

disease.

Annu.

Rev.

Phytopath.

47:

177-206,

permission

conveyed

through

Copyright

Clearance

Center,

Inc..Salicylic

acid

O-β-glucosideSalicyloyl

glucoseesterMethylsalicylateMethyl

salicylate

O-β-glucosideMost

SA

is

synthesized

in

thechloroplast,

conjugated

in

the

cytoplasmand

sequestered

in

the

vacuoleplastidMeSAICSSASAG

(Salicylic

acid

O-β-glucoside)SASAGSGE-glucose-glucoseSGE

(Salicyloyl

glucose

ester)Cell-to-cell

movement

of

SA

mayinvolve

multiple

mechanismsRocher,

F.,

Chollet,

J.-F.,

Legros,

S.,

Jousse,

C.,

Lemoine,R.,

Faucher,M.,Bush,D.R.andBonnemain,

J.-L.

(2009).

Salicylic

acid

transcommunis

involves

a

pH-dependent

carrier

system

in

addition

to

diffusion.

Plant

Physiol.

150:

2081-2091.SA-

+

H+SA-HSA-HSA-

+

H+SAAs

a

weak

acid,

SA

isuncharged

in

the

acidiccell

wallandnegativelycharged

in

the

cytoplasm,leading

to

an

“ion

trap”mechanism

of

uptake(similar

to

that

of

auxin)There

is

also

evidence

that

SA

uptake

into

thecell

may

occur

via

aprotein

carrier,

as

it

doesin

animal

cellsRegulation

of

SA

accumulationBacterialpathogenFungal

oroomycetepathogenICS1SAPathogeneffectorsOther

stress(e.g.

UV

light)SA

synthesis

isinduced

by

pathogens

or

stress.Genetic

studies

have

identified

some

of

the

signalsthat

transducepathogenperception

to

SAsynthesisThe

eds1

mutant

shows

enhanceddisease

susceptibilityParker,

J.E.,

Holub,

E.B.,

Frost,

L.N.,

Falk,

A.,

Gunn,

N.D.,

and

Daniels,

M.J.

(1996).

Characterization

of

eds1,

a

mutation

in

Arabidopsis

suppressiPeronospora

parasitica

specified

by

several

different

RPP

genes.

Plant

Cell

8:

2033-2046.eds1Wild

type:Pathogengrowth

isarrested

by

Wild-typeplantdefenseresponseeds1:Plant

fails

torespond

andpathogengrowth

isuncheckedThe

eds1

mutant

is

deficient

in

PR1gene

expression

but

rescued

by

SAFalk,

A.,

Feys,

B.J.,

Frost,

L.N.,

Jones,

J.D.G.,

Daniels,

M.J.,

andParker,

J.E.

(1999).

EDS1,

an

essential

componentof

R

gene-mediateddisease

resistancehomology

to

eukaryotic

lipases.

Proc.

Natl.

Acad.

Sci.

USA

96:

3292-3297

copyright

1999

National

Academy

of

Sciences

USA.Wild-typeeds1PathogenrecognitionEDS1DefenseresponseNoPR1inductionbypathogenSAEDS1

and

PAD4

are

related

lipase-like

proteins

that

form

a

complexReprinted

by

permission

from

Macmillan

Publishers

Inc

(EMBO)

Feys,

B.J.,

Moisan,

L.J.,

Newman,

M.-A.,

and

Parker,

J.E.

(2001).

Direct

interaction

between

Arabidopsis

disease

resistance

signaling

proteins,

EDS1

and

PAD4.

EMBO

J

20:

5400-5411.

Zhou,

N.,

Tootle,

T.L.,

Tsui,

F.,

Klessig,

D.F.,

and

Glazebrook,

J.PAD4

functions

upstream

from

salicylic

acid

to

control

defense

responses

in

Arabidopsis.

Plant

Cell

10:

1021-1030.The

pad4mutant

isdeficient

in

SAaccumulationEDS1

/

PAD4

/SAG101DefenseresponsePathogen

Pathogenrecognition

recognitionNDR1Other

genesare

alsoneeded

forpathogen-induced

SAaccumulationSSAARegulation

of

SA

accumulationBacterialpathogenFungal

oroomycetepathogenICS1SAPathogeneffectorsOther

stress(e.g.

UV

light)PAD4

/EDS1/SAG101NDR1Additionalmutants

withaltered

SAaccumulationcontinue

to

becharacterizedSynthesis,

conjugation

andtransport

of

SA

-

summary

SA

accumulation

is

correlated

with

ICS1

andPAL

expression

Other

factors

necessary

for

SA

synthesis

havebeen

identified

and

their

molecular

functionsare

under

investigationSA

activity

canbe

modified

by

conjugation

There

is

evidence

for

carrier-mediatedtransport

of

SAImage

credit:

Prof.

Dr.

Otto

Wilhelm

Thomé

Flora

von

Deutschland,

Österreich

undderSchweiz

1885,

Gera,

GerPerception

and

signalingSAPRSA

induces

anenormoustranscriptionalresponseWard,

E.R.,

Uknes,

S.J.,

Williams,

S.C.,

Dincher,

S.S.,

Wiederhold,

D.L.,

Alexander,

D.C.,

Ahl-Goy,

P.,

Metraux,

J.P.

and

Ryals(1991).Coordinate

gene

activity

in

response

to

agents

that

induce

systemic

acquired

resistance.

PlantCell.

3:

1085-1094.PR

genes

arepathogenesisrelated

genes,and

are

involvedin

defenseresponsesThe

red

arrows

indicate

the

SA-signalinggenes

that

are

upregulated

by

SA,

amplifying

thesignal.ICS1EDS1PAD4NPR1Several

WRKYs(transcription

factors)Many

genes

respond

to

SA:

Earlygenes

amplify

the

signalEarlyLateAdapted

from

van

den

Burg,

H.A.,

and

Takken,

F.L.W.

(2009).

Does

chromatin

remodeling

mark

systemic

acquiredresistance?

Trends

Plant

Sci.

14:286-PathogenrecognitionEDS1

/

PAD4TranscriptionresponseICS1NPR1PR-1PR-5BGL2NIMIN1ATNUDT6FRK1Several

WRKYs(transcription

factors)SAThe

plant

on

the

right

is

supporting

alot

of

pathogen

growth,

which

appears

as

awhite

fuzz

on

the

leaf

surfaces

(the

disease

caused

by

thispathogen

is

called

downy

mildew).Delaney,

T.P.,

Friedrich,

L.,

and

Ryals,

J.A.

(1995).

Arabidopsis

signal

transduction

mutant

defective

in

chemically

and

biologically

inducedProc.

Natl.

Acad.

Sci.

USA

92:

6602-6606

copyright

1995

National

Academy

ofSciences

USA.NPR1

is

a

major

activator

of

SA-mediated

responsesWild-type

npr1(akanim1)Plants

were

treated

with

SA,

then

three

dayslater

challenged

with

a

fungal

pathogen(Hyaloperonospora

arabidopsidis)NPR1(NONEXPRESSOR

OFPATHOGENESIS-RELATEDGENES1)

isnecessary

fordefenseresponses

andat

the

core

ofSA

signaltransductionOn

the

left,

the

npr1

mutant

leaves

are

very

sick,

and

do

not

induce

PRgene

expression

(shown

as

blue

GUS

staining

in

the

lower

panel).

In

thepanel

to

the

right,

the

plant

overexpressing

NPR1

shows

reduced

pathogen

growth

(shown

by

reduced

trypanblue

staining).NPR1

is

necessary

and

sufficient

fordownstream

signaling

and

defenseReprinted

from

Cao,

H.,

Glazebrook,

J.,

Clarke,J.D.,

Volko,

S.,

and

Dong,

X.

(1997).The

Arabidopsis

NPR1

gene

that

controls

systemic

acquired

resistance

enprotein

containing

ankyrin

repeats.

Cell88:

57-63

with

permission

from

Elsevier;

Cao,

H.,

Li,

X.,

and

Dong,

X.(1998).Generation

ofbroad-spectrum

diseaseoverexpression

ofanessential

regulatorygeneinsystemicacquired

resistance.

Proc.

Natl.Acad.Sci.

USA

95:6531-6536

copyright

National

Academy

of

ScieWild-type

npr1Loss

of

function:more

susceptibleGainof

function:more

resistantNPR1Pseudomonas

syringae

infectionPR

geneexpressionResistanceBgl2-GUS

(PR

gene)

expressionSAThen

panel

on

the

right

shows

confocalimages

of

NPR-GFP

fluorescence

in

mesophyll

cells,

withGFP

fluorescence

shownin

the

green

channeland

differential

interference

contrast

in

the

red

channel.NPR1

oligomerizes

via

redox-sensitive

cysteinesHSSHSSReductionOxidizationSA

accumulation

contributes

to

areducing

environment,

which

causesmultimeric

NPR1

to

monomerizeNPR1NPR1NPR1NPR1NPR1NPR1NPR1Monomeric

NPR1

isimported

into

the

nucleus(here

it

is

GFP-labeled)SANPR1SASAKinkema,M.,Fan,W.,and

Dong,X.(2000).Nuclearlocalization

of

NPR1

is

required

for

activation

of

PRgeneexpression.

Plant

Cell

12:

2339NPR1,

NPR3

and

NPR4

have

recentlybeen

reported

as

SA

receptorsIn

mid-2012,

two

groups

reported

that

membersof

the

NPR

family

serve

as

SA

receptorsFu,

Z.Q.,

Yan,

S.,

Saleh,

A.,

Wang,

W.,

Ruble,

J.,

Oka,

N.,

Mohan,

R.,

Spoel,

S.H.,

Zheng,

N.

and

Dong,

X.

(2012)

NPR3

and

NPR4

are

receptors

for

the

immune

signalsalicylic

acid

in

plants.

Nature

(in

press)

doi:10.1038/nature11162.The

two

groups

used

differentassays

to

characterize

SAbinding,

leading

to

differentconclusionsNPR1

isregulated

directlyby

SA

bindingand

/

orNPR3/4

bindSA

andregulate

NPR1Model:

NPR3

and

NPR4

regulate

theproteolytic

turnover

of

NPR1LOW

[SA];

someNPR1

accumulatesUninfected

plantInfected

plantVERY

HIGH

[SA];NPR1

degraded,celldeath

occursIntermediate

[SA];some

NPR1accumulates

andactivates

defensesFu,

Z.Q.,

Yan,

S.,

Saleh,

A.,

Wang,

W.,

Ruble,

J.,

Oka,

N.,

Mohan,

R.,

Spoel,

S.H.,

Zheng,

N.

and

Dong,

X.

(2012)

NPR3

and

NPR4

are

receptors

for

the

immune

signalsalicylic

acid

in

plants.

Nature

(in

press)

doi:10.1038/nature11162.NPR1

binds

SA,

triggering

a

conformationalchange

that

releases

its

C-terminal

activatidomain

from

inhibition

to

trigger

transcriptWu,

Y.,

Zhang,

D.,

Chu,

J.Y.,

Boyle.

P.,

Wang,

Y.,

Brindle,

I.D.,

De

Lucy,V.

and

Després,

C.

(2012)

The

Arabidopsis

NPR1

protein

is

a

receptor

for

the

plant

defensalicylic

acid.

Cell

Rep.

1:

639-647.Model:

NPR1

itself

is

activated

bybinding

to

SAIn

the

nucleus,

SA-activated

NPR1promotes

transcriptionNO

SA+

SA-TGAs-WRKYsNPR1+TGAs+TGAs+WRKYsIn

the

absence

of

SA

andactivated

NPR1,

negativeregulators

repress

defense

genesIn

the

presence

of

SA

andactivatednuclear

NPR1,

positive

regulatorsactivate

defense

genesNPR1

binds

TGA

transcriptionfactors

and

promotes

DNA

bindingZhang,

Y.,

Fan,

W.,

Kinkema,

M.,

Li,

X.,andDong,

X.

(1999).

Interaction

of

NPR1

with

basic

leucine

zipper

protein

transcription

factors

that

bind

sequence

salicylic

acid

induction

of

the

PR-1

gene.

Proc.

Natl.

Acad.

Sci.

USA

96:

6523-6528;

Despres,

C.,

DeLong,

C.,

Glaze,

S.,

Liu,

E.,andFobert,

P.R.

(2000).

Th

NPR1/NIM1

protein

enhances

the

DNA

binding

activity

of

a

subgroup

of

the

TGA

family

of

bZIP

transcription

factors.

Plant

Cell

12:

279-290.Yeast-two

hybridassay

showingNPR1/

TGAinteractionNPR1+TGAsNPR1+TGAsFreeDNABoundDNADNA

bindingof

TGA2

isenhancedby

NPR1The

Arabidopsis

genomeencodes

10

TGA

factors.

Someare

positive

and

some

negativeregulators

of

defense

genes-TGAs-TGAs+TGAs+TGAsTGA2

is

both

a

repressor

and

anactivator

of

transcriptionBoyle,

P.,

Le

Su,E.,

Rochon,

A.,

Shearer,

H.L.,

Murmu,

J.,

Chu,J.Y.,

Fobert,

P.R.,and

Despres,

C.

(2009).

The

BTB/POZ

domain

ofArabidopsis

disease

resistance

protein

NPR1

interacts

with

the

repression

domain

of

TGA2

to

negate

its

function.

Plant

Cell

21:SA

/

NPR1NPR1NPR1-binding

toTGA2

masks

itsrepressor

domainandactivatestranscriptionWRKYs

are

a

large

family

oftranscription

factorsThere

are

74

Arabidopsis

WRKYs

and

90rice

WRKYs,

many

of

which

are

involvedin

defense

signaling.

Some

promote

andsome

repress

transcription-WRKY+WRKYGenes

induced

by

WRKYsinclude

NPR1

and

ICS1

→signal

amplification!SA+WRKYICS1NPR1NPR1These

gels

shownorthern

blotsof

WRKYs

and

PR1

athours

after

the

culture

was

elicited.WRKYs

were

characterized

inparsley

cell

culturesInteraction

of

elicitor-induced

DNA-binding

proteins

with

elicitor

response

elements

in

the

promotersof

parsley

PR1

genes.

P

J

Rushton,

JTParniske,

P

Wernert,

K

Hahlbrock,

and

I

E

Somssich

EMBO

J.

1996

October

15;

15(20):

5690–5700.WRKY

transcriptionfactors

werecharacterized

asactivators

of

PR1

geneexpressionWRKY

=

Trp-Arg-Lys-TyrThe

network

of

WRKY

transcriptionfactor

interactions

is

complexReprinted

from

Eulgem,

T.,

and

Somssich,

I.E.

(2007).

Networks

of

WRKY

transcription

factors

indefense

signaling.Curr.

Opin.

PlantBiol.10:

366-371

with

permission

from

Elsevier.This

large

family

oftranscription

factorscontrols

expressionof

many

defensegenes.

Some

areactivators,

somerepressors,

one

is

aresistance

protein,and

some

are

directtargets

of

resistanceproteinsThe

MLA

resistance

protein

inhibitsa

negative-acting

WRKYShen,

Q.-H.,

Saijo,

Y.,

Mauch,

S.,

Biskup,

C.,

Bieri,

S.,

Keller,

B.,

Seki,

H.,

Ülker,

B.,

Somssich,

I.E.,

and

Schulze-Lefert,

P.

(2007).

Nuclear

activity

oreceptors

linksisolate-specificand

basal

disease-resistance

responses.

Science

315:

1098-1103.

Reprinted

with

permssion

from

AAAS.When

barley

perceives

the

pathogen,the

MLA

protein

moves

into

thenucleus

and

inhibits

repressiveWRKYs

to

activate

PR

genesThe

complexity

of

defensegene

regulation

protectsmakes

it

hard

for

pathogensto

defeat

and

providesflexibility

and

specificity

toresponseThe

PR-1

promoter

is

subject

tochromatin

modificationMosher,

R.A.,

Durrant,

W.E.,

Wang,

D.,

Song,

J.,

and

Dong,

X.

(2006).

A

comprehensive

structure-function

analysis

of

Arabidopsis

SNI1

defines

essential

rtranscriptional

repressor

activity.

Plant

Cell

18:

1750-1765.SAHistone

modifications

thatactivate

transcription

areenriched

by

SA

treatment+SA+SAIn

the

absence

of

SA:Gene

OFFIn

the

presence

of

SA:Gene

ONThe

panel

on

the

top

left

seems

abit

counter-intuitive,

but

in

this

case

the

HDA19

is

silencinganinhibitorof

PR-1,

so

overexpression

of

HDA19causeamore

vigorous

defense

response

and

more

resistance.Histone

deacetylase

activity

iscorrelated

with

pathogen

responseKim,

K.-C.,

Lai,

Z.,

Fan,

B.,

and

Chen,

Z.

(2008).

Arabidopsis

WRKY38

and

WRKY62

transcription

factorsinteract

with

histone

deacetylase19in

basal

defense.

Plant

Cell

20:

2357-2371.HDA19had19-3

WT

HDA19-OELessresistantMoreresistantHistone

deacetylationleads

to

a

closedchromatin

state

andinactive

genesHDA19WKRY-WRKYPR-1HDA19

turns

offthe

gene

encodinga

repressiveWRKY,

leading

toenhanced

PR-1expressionsni1

is

a

suppressor

of

npr1Li,

X.,

Zhang,

Y.,

Clarke,

J.D.,

Li,

Y.andDong,

X.

(1999).

Identificationandcloning

of

a

negative

regulator

of

systemic

acquired

resistance,

SNI1,

throug

suppressors

of

npr1-1.

Cell.

98:

329-339.

Wang,

S.,

Durrant,

W.E.,

Song,

J.,

Spivey,

N.W.,andDong,

X.

(2010).

Arabidopsis

BRCA2andRAD51

proteins

are

spec

involved

in

defense

gene

transcription

during

plant

immune

responses.

Proc.

Natl.

Acad.

Sci.

USA

107:

22716-22721.npr1

=

no

PR

expressionnpr1sni1

=

suppressor

of

npr1

=

constitutive

PRexpressionIn

the

sni1

mutant,

PR-1genes

are

expressed

allthe

time

even

in

non-inducing

conditionsSNI1

maintains

a

low

level

ofexpression

in

non-inducing

conditionsMosher,

R.A.,

Durrant,

W.E.,

Wang,

D.,

Song,

J.,

and

Dong,

X.

(2006).

A

comprehensive

structure-function

analysis

of

Arabidopsis

SNI1

defines

essential

rtranscriptional

repressor

activity.

Plant

Cell

18:

1750-1765.SNI1Activating

histone

marksare

increased

in