plnt mcrb intract rev

7/29/2019 Plnt Mcrb Intract Rev

1/65

Plant Microbe Interaction

&Examples

1


2/65

Plant-Microbe Interactionsz

Symbiotic- endophytic ?

-

- Actinomycetes - Frankia

- Bacteria Rhizobium

Associative Pathogenic

-

- Necrotrophs

z - PGPR

- Biocontrol

2

z

Future advances in PMI- Molecular biology and genomics


3/65

ant- cro e nteract ons

z

Associative - various bacteria/fungi - synthesize growth regulators- -

- Azospirillum - N2 fixation

- -z Symbiotic endophytic ?

- mycorr zae - m nera sa on

- non-leguminous nodules Frankia-Alnus - N2

fixation

- egum nous no u es zo um- egumes - 2 xa on

3

z Pathogenic - Biotrophs

- Necrotrophs


4/65

Location of interaction

Rhizosphere. Root zone. A very narrow zone (a few mm) around the root.Contains root exudates and microbes.Phyllosphere. Leaf surface as a habitat for microbes

rhizosphere is a relatively stable, nutrient-rich environment. Phyllosphere isan extreme environment


5/65

Densities of microorganisms in

rhizosphere

Decreasing

microbial

diversity


6/65

ssoc a ve m croorgan sms

z

Can affect the mineral nutrition of plants

physiology and development of plants

availability of nutrients

nutrient uptake processesz Numerous bacteria and fungi synthesize plant growth

. . , , -

be selective e.g auxins cf. gibberellins by Pine rhizosphere

organismsz Microorganisms also enhance plant growth through suppression

of pathogens and deleterious microbes

-

6

. . .

inhibit pathogens


7/65

ssoc a ve m croorgan sms

z Free-living microbes can also

impact on N & P availability 2 -

found in rhizosphere of grasses,corn, wheat e.g. Bacillus sp.,Enterobacter sp. Azospirillumsp. zo o ac er sp.

Also found in the ECM ofDouglas fir

growth - offers potential forfuture exploitation - conditions

supporting N2 fixation ac er a ncrease ava a y -

through solubilisation of rockphosphates

U take P into m corrhizal lants

7

greater in presence of free-living

organisms and mycorrhizae


8/65

Endophytes

z All plants are infested with microbes

Symptomless

Balanced status of symbiosis

.

Disease

a ogens

Unbalanced status of symbiosis


9/65

n op y ez n en op y e s an en osym on , o en a ac er um or

fungus, that lives within a plant for at least part of its life.

from parent to offspring) or horizontally (from individual to.

z Endo h tes. Live within lant tissues intracellularl typically commensals or symbionts

many strains ofKlebsiella are also co-evolved N-fixing endophytic

Salmonella, E.coliare now recognized as commensal endophytes


10/65

Rhizosphere

z Rhizoplane

soil in direct contact with

plant root

z Endo h tes

microbes attached to

root surface

Decreasing moistureIncreasing organic C


11/65

Symbiotic organisms

ycorr zaez Mycorrhizae

Most plants are mycorrhizal:fun us receives C for rowth

plant greater acquisition of

nutrients

spores/vegetative propagules inroot fragments

by root exudates (Bowen, 1994),

chemotropism to root via

exudates Tawara a et al 1998

3 types

Arbuscular

`

11

c o

Ericoid


12/65

ym o c organ sms

z Mycorrhizal plants benefit in

several ways

greater resistance to pathogens

- physical protection, production

of toxins, rhizos here

modification to inhibit pathogen Better nutrition - P - increased

root surface area & access

organic P?

P uptake also enhanced further

in resence of free-livinorganisms

12


13/65

on- egum nous no u es

z 200 dicotyledonous plants form non-

leguminous N2 fixing nodules after-

sp., all but 2 are woody and found intemperate regions and tropics

z Most prominent is Frankia sp. wither

z At present interaction thought to benon specific

legumes by Rhizobium sp. suggestsprobable role in Frankia-Alder

symbiosis but not establishedz ea rea men o roo exu a es o

alder prevented Frankia infection -suggesting proteins in exudates areinvolved in symbiosis

13


14/65

on- egum nous no u es

z Most Frankia -associated plants also form mycorrhizal

s mbioses - tri artite association

z Synergistic - both N2 fixation and plant growth increased

z Under low N & P - mycorrhizae enhance P uptake - benefiting

Frankia - Frankia enhance N2

fixation enhancing root growth and

mycorrhizal development

z Substantial N fixation b Frankia oints to benefits of lantin

Alder with other trees

z

Increased knowledge of role root exudates in the symbiosis may

14


15/65

egum nous no u es

z Tropical leguminous trees

e.g. Acacia form symbioticassoc a ons w zo um

z Infection of trees - directentry between root epidermalcell walls to the cortical cellsto form nodules

z Contrast to herbaceouslegumes where infection isthrough root hairs - suggests

host specific recognitions gna s recogn se yRhizobium from herbaceouslegumes are absent from

15

rees


16/65

a ogen c m croorgan sms

z Bacterial

z Agrobacterium tumefaciens , ,

grape vines

.

campestris - brown rot -cabbage and cauliflower leaves.

z X. campestris pv. oryzae -leaf.

z X. campestris pv. citri- citruscanker.

z Pseudomonas solanacearum. -vascular wilt diseases of a rangeof crops

16


17/65

a ogen c m croorgan smsz Fungal & bacterial

z Biotrophic pathogens establish intricate feeding relationship with host cellsz Nectrophic pathogens invade plant tissue aggressively killing host cells

Biotrophs

Phytophthora >60 speciesinfestans potato blightso ae so bean bli htramorum sudden oak death

Powder mildew fun i Ascom cetes

Sphaerotheca pannosa - rosesmors-uvae gooseberryErwinia graminis cereals and grasses

Rust fungi Basidiomycetes

Puccinia graminis cereals and barberryPuccinia unctiformis thistle rust

17

Melampsoridium betulinum birch rust


18/65

a ogen c m croorgan sms .

Heterobasidion annosum - conifers

18Heart rot fungi Ganoderma adspersum, a white-rot fungus - heartrot of beech and other broadleaved trees


19/65

Biotechnological applications of


z PGPR plant growth promoting rhizobacteria Produce plant growth regulators

2

Mineralize P

Enhance mycorrhization

-

19


20/65



z Mycorrhization Helper Bacteria -MHB (mainly Pseudomonas sp.and Bacillus sp.) may berespons e or se ec on process

First isolated from Douglas fir -Laccaria laccata system - foundto be fungus specific (Duponnois& Garbaye, 1990)

Promote establishment ofL.

laccata on wide range trees, butinhibit other mycorrhizae

May modify exudates to enhance

to produce different compoundsor stimulate mycorrhizal fungidirectly (Garbaye, 1994)

Specificity of MHBs confirmed-inoculation offers exitingprospect for future

20


21/65


ant- cro e nteract onsz Phlebiopsis gigantea control of

Heterobasidion annosum

z Most dama in root atho en of coniferoustrees in the Northern hemisphere

z Spreads progressively by contact of healthyroots with infected roots, causing disease

a s A ma have bracket-sha edfruitbodies of Heterobasidion at their base

(C). Fruitbodies release air-bornebasidiospores - spread infection to newsites. Occurs typically when trees are felled.

surfaces - fungus grows down throughstump tissues to the dead roots- theninfects roots of adjacent healthy trees.

.hyphae ofH. annosum (and some otherfungi) on contact - hyphal interference (G).Any hypha ofH. annosum making contact

21

. ,localised disruption: the protoplasm

becomes disorganised and its membraneintegrity is affected (dye taken up).


22/65



z Use of pseudomonads to controlthe take-all fungus,Gaeumannomyces graminis

z Major root-rot pathogen ofcereals and grasses. Survives inthe infected residues of onecrop, then invades the roots ofthe following crop. Exceptionalcases kills whole crop; hence the

name "take-all".z G. graminis also causes a patch

disease of turf grasses,es eciall of A rostis s ecies(the "bent grasses") which areused in high-quality turf such ason bowling greens and golf-course greens.

z Fluorescent pseudomondsproduce phenazine antibioticswhich kill Gg - these antibiotic-producing bacteria might be

22

coatings, to prevent or reduce

take-all or other root diseases.


23/65

Biotechnological applications of Plant-

Microbe Interactionsz gro ac er um ra o ac er s ra n

control ofAgrobacterium tumefaciensz Agrobacterium tumefaciens causes crown

gall disease on dicotyledonous (broad-leaved) plants, - apple, pear, peach, cherry,almond, raspberry, roses, grapevine.

z Bacterium transfers part of its DNA to theplant, - DNA integrates into the plantsgenome, causing the production of tumours

metabolism.

z Agrobacterium radiobacter strain K84produces a bacteriocin -agrocin 84 - enters

synthesis.

z Unique mode of action ofA. tumefaciens -enabled this bacterium to be used as a toolin plant breeding

Plants have been engineered to express theBt gene - insects attempting to eat theseplants are killed.

23

to herbicides e.g. glyphosate - herbicide can

be used for weed control without damagingthe crop. E.g. "Roundup Ready" Monsantocrops soybean, canola, cotton


24/65

u ure a vances nz New advances molecular biology unlocking

secrets of black box of unknown soilorganisms Identifying new

organisms/enzymesz Biotechnological applications Biocontrol Genetic engineering of plants - pesticide and

herbicide resistance Biocatalysis next decade 90% processes Bioremediation eg. Wood decay fungal

enzymes detoxify pollutants, delignifya ricultural wastes leave cellulose ascheap commercial substrate

z Functional Genomics microarrays poisedto revolutionise our understanding and

ex loitation of PMI E.g. Projects now being funded to sequence

genes in Phytophthora involved in infectionprocess

Microarra s which enes are turned on in

24

plants and pathogens during infection


25/65

-INTERACTION


26/65

Nitrogen fixing organisms:

representat ve o sym ot c acter a


27/65

on egume

Alder is a N-fixing plant that

forms a symbiotic association

with bacteria (more specifically Gunnera sp., an unusualan ac nomyce e o e genus

Frankia. There are about 21

-

contains nitrogen-fixing

N, called actinorhizal plants . at the base of petioles


28/65

egume

Fabaceae) includes many important cropspecies such as pea, alfalfa, clover, common

bean, eanut, and lentil

soybean pea

R l i bi


29/65

R.leguminosarum biovarviciae colonizes pea ( Pisum

spp.

. .clover ( Trifolium spp)

R l biovar phaseoli colonizesbean ( Phaseolus spp.)

Bradyrhizobium japonicum

Rhizobium NGR 234 colonizesParasponia and tropicalplants; very broad host range


30/65

Nodule development process

z

1. Bacteria encounter root;z ey are c emo ac ca y a rac e owar spec cplant chemicals (flavonoids) exuding from root

,


31/65

2. Bacteria attracted to the root, attach themselves to

specific oligosaccharide signal molecules (nod.


32/65

. n response o o gosacc ar e s gna s, e

root hair becomes deformed and curls at thetip; bacteria become enclosed in small pocket.

root.


33/65

4. Bacteria then invade the root hair cell and move along an

n erna , an - er ve ,z multiplying, and secreting polysaccharides that fill the

.

infection threa

Rhizobium cells expressing GFP

host root hair


34/65

z 5. Infection thread penetrates through several layers ofcortical cells and then ramifies within the cortex. Cells in

nodule primordium.

z . e ranc e in ection t rea enters t e no u eprimordium zone and penetrates individual primordium cells.

z 7. Bacteria are released from the infection thread into thecytoplasm of the host cells, but remain surrounded by theper ac ero mem rane. a ure o orm e resu s nthe activation of host defenses and/or the formation of

ineffective nodules.

z 8. Infected root cells swell and cease dividing. Bacteria

endosymbiotic bacteroids, which begin to fix nitrogen.


35/65


36/65

z The nodule provides an oxygen-controlled environment

(leghemoglobin = pink nodule interior) structured to facilitateto the plant vascular system, and of photosynthate from the

.


37/65

Patriarca et al. 2002. Microbiology and Mol. Biol. Rev.-

R


38/65

SUMMARY :1. NodD rotein reco nition of different com ounds in root exudates

(flavonoids) contributes to host specificity.2. The nod genes encode functions that are involved in the regulation ofgene expression (e.g., NodD), producing the core Nod factor (NodABC)an ecora ng no ac ors sn,e.g., o , o .

3. Differences in Nod factor decoration (side chain modifications)

contribute to specificity.

z Specificity is a due to a combination of factors:1. Types of flavonoids made by host plants2. Nod D sensor proteins in the bacterial symbionts3. Types of Nod factors produced by the bacteria4. Amounts of Nod factors roduced b the bacteria5. Exopolysaccharide - for indeterminant nodules (role unclear)6. Plant hydrolases (e.g. chitinases that may degrade Nod factors)

-. bacteria to plant cells)8. Plant receptors for Nod factors

z nodC gene encodes NodC protein an enzyme with N acetyl


39/65

z nodC gene encodes NodC protein - an enzyme with N-acetyl-glucosaminyltransferase activity. Synthesis of the N-acetyl-

.z nodB gene encodes the NodB protein - a deacetylase enzyme that

removes an acetyl group from the Nod factor.-

fatty acid chain to the site deacetylated by NodBz Sulfation ( nodH, noeE). Sulfotransferases that modify Nod factors

,z Fatty acid addition ( nodEF). Different NodEF proteins from different

Rhizobium species can put different fatty acids onto Nod factors andchan e s ecificit .

z

Arabinosylation ( noeC). The NoeC protein adds arabinose to Nodfactors - can influence number of nodules that are formed on hostplants.

z Fucosy ation e.g., no Z . Fucose a ition c anges speci icity onodulation for some symbionts such as Bradyrhizobium japonicum.

z

Acetylation (e.g., nodL). Acetlyation can influence Nod factor activityor . egum no aruman . a on cumz Methylation and Carbamoylation (e.g., nodS). Mutation changes host

range for R. tropici, R. loti, R. frediiand B. japonicum.


40/65

Factors Affecting Nitrogen Fixation

-- - . .,

nodulation decreasesSoil potassium level -- as soil potassium level decreases - number and size of

Soil nitrate level -- as soil nitrate level increases, infection, nodulation, nodule

growth, and amount nitrogen fixation decreases

roc multiplication of rhizobia at or near the root surface

Gene

roa adhesion of rhizobia to root hair surface

hab and hac root hair branching and root curling

inf formation of an infection thread

noinodule initiation: formation of nodulemeristem, nodule development and differentiation

bad bacterial differentiation

nif onset of nitrogen fixation

cofbiochemical and physiological functions

associated with nitrogen fixationnop maintenance (persistence) of nodule function


41/65

M corhizae


42/65

Soil and Site Factors Influencing Mycorrhizas

1. Mycorrhizal Inoculum mycorrhizal fungi is present in most soils.

mycorrhizal fungi may be absent from soils where severe. o s ur ance soil disturbance has resulted in topsoil loss, or where host

plants are limited by adverse soil or site factors such as

salinit aridit waterlo in or climatic extremes

3. Soil Fertility High rates of P and N fertilizers suppress ectomycorrhiza

development in the field4. Adverse Soil Conditions Excessive NaCl in soil inhibit mycorrhizal formation and

restrict the activity of most mycorrhizal fungi, but some

ECM fungi can be highly sensitive to waterlogging ofsoils, while VAM fungi may be less sensitive


43/65

Infection process (VA Mycorrhizae)

1. root grows nearby2. spore germinates

3. enetration

4. arbuscules form, then

5. produce external spores


44/65

z before symbiosis takes place, the germinating spores need certain factors toromote h hal rowth. At this sta e the fun us is still tro hicall de endent

on spore reserves, and it has been proposed that some root exudates regulatethe ability of the fungus to use its endogenous reserves

z avono s pay an mpor an roe n mycorr za sym oses.

z The flavanones hesperitin and naringenin and the flavone apigenin stimulated

z The two isoflavones formononetin and biochanin A and, to a lesser extent, theflavone chrysin have been shown to stimulate formation of VA mycorrhizaebetween a Glomus sp. and white clover.

z The flavonol glycoside quercetin-3-O-galactoside, 4',7-dihydroxy flavone, and

', - , ,enhanced spore germination of two Glomus species

Agrobacterium


45/65

Agrobacterium


46/65


47/65

Acetosyringone: Phenolic compound, alpha-Hydroxyacetosyringone,Catechol,Ferulic acid,Gallic acid,p-Hydroxybenzoic acid

Protocatechuic acid,Pyrogallic acid,Resorcylic acid, sinapinic acid,Syringic acid,Vanillin


48/65


49/65


50/65


51/65


52/65


53/65


54/65


55/65


56/65


57/65


58/65

ow a ogens ac an s

a ogens a ac p an s ecause ey ave evo ve e un que

ability to gain access to plant tissues and live off their contents

In order to do cause disease, pathogens must be able to:

1. Recognize the host

2. Penetrate host barriers

3. Move (invasion) through host tissues

. z nu r on or grow an

reproduction

. ,systems


59/65

Tactic response allows zoospores to reach

n ect on s tes n roots o ost p ants

Positive chemotaxis towards plant

compounds (ex: P. sojae to isoflavones)

Electrotactic responses also noted (weak

electric fields generated by roots)

Phytophthora and Pythium zoospores swim towards

Pythium zoospores swimming to root caps

z B. Surface sensing (Thigmotropism and Chemical signals)z This rocess is best chacterized for rust s ores Urom ces Puccinia


60/65

z This rocess is best chacterized for rust s ores Urom ces, Puccinia

z The spore reorients the direction of germ tube growth based on cues from thehost plant surface. For example, Puccini graminis germlings grow perpendicular to

.appropriate points of entry.

z Uromyces germlings will recognize topographical features of a surface (leaf

stomate guard cells, artificial surfaces with grooves or ridges) and differentiatento an appressor um. e s gna or erent at on s a c ange n e evat on o .micrometres.

Sugars, Potassium and Calcium for rust fungiz Cutin monomers or lipid monomers for Magnaporthe grisea and Colletotrichums ecies.

z Secondary messenger molecules can triggerinfection structure formation, e.g.,

(cAMP) can trigger appressorium formationin M. grisea.


61/65

.- a spore lands on the plant surface.

adhesion : hydrophobic interactions with the plant cuticle.

After the spore germinates and forms a germ tube, a film is secreted

to surround the germ tube and presumably attach it to the surface.

e.g. hydrophobins that are bound to the fungal germling cell surface.The sheath may also contain degradative enzymes (such as cutinase)

.

Magnaporthe grisea (Rice Blast fungus) is an exception : The spore tips contain a

the leaf surface (even in the presence of flowing water). This fungus also senses

surface hardness, and surface hydrophobicity

a)Bacterial

movement


62/65

movement

(swimming) onlant

surface.

b)Bacterial

multi lication on

surface/andinvasion of the

apoplast.

c)Flagellin

reco nition and

subsequent

res onse.


63/65

z Some bacteria use uorum sensin to monitor their local o ulation densit . Theaccomplish this by secreting and monitoring small diffusible signaling molecules. andwhen the concentration reaches a threshold, receptors signal a change in geneexpression.

z N-acyl homoserine lactones are the most common types of signaling molecules thatbacteria use for quorum sensing.

z an pa ogen c ac er a use quorum sens ng o con ro pa ogenes s an co on za on

of the host.z Thus uoru sensin is used or :1. Production of extracellular polysaccharides2. Production of degradative enzymes3. Production of siderophores (low molecular weight iron binding factors)4. Expression of type III secretion apparatus (hrp genes).5. Transfer of the Ti plasmid between strains of Agrobacterium tumefaciens.


64/65

General steps/components involved

in a response (signal transduction)


65/65

are conserved

between insects, plants and

animals.

1. Ligand binding to a Receptor

2. Signaling across the membrane

.

phosphorylation cascade. Often thisinvolves mitogen

ac va e pro e n nases s

4. Activation of transcription factors

5. Change in gene expression -

defense enes

plnt mcrb intract rev

Documents