host nematode interaction

SEMINAR ON HOST- NEMATODE INTERACTION

VINOD UPADHYAYM-10140

M.Sc.(Ag) Final yr.MPP,IASc., BHU.

INTRODUCTION Plant parasitic nematodes - obligate parasites, -obtaining nutrition from the cytoplasm of

living plant cells.

Damage food and fiber crops throughout the world and cause billions of dollars in losses annually .

According to parasitism :• Ectoparasites- living outside their host causing

severe root damage and can be important virus vectors .

• Endoparasites- spend much of their lives inside roots .They may be migratory or sedentary endoparasites.

• Migratory endoparasites -move through the root, causing massive cellular necrosis.

• Sedentary endoparasites- completely embedded in the root - initial stages of development but later become sessile after entering into the root tissue.

Sedentary endoparasites of the family Heteroderidae that cause the most economic damage worldwide.

The Heteroderidae - two groups: 1.Heterodera and Globodera= cyst

nematodes, 2. Meloidogyne =root-knot nematodes .

Soybean cyst nematode (Heterodera glycines), Potato cyst nematodes (Globodera pallida ,

G.rostochiensis) Root-knot -most economically important .

Symptoms of diseased plants - stunted growth - yellowing - wilting - susceptibility to

other pathogens.

II Stage juvenile invade rootand cause formation of syncytia

IIl Stage male and femalejuvenile feeding on syncytia

IV Stage juveniles

Syncytium of malebegins to degenerate

Adult nematodes

II Stage juvenilesattack young roots

II Stage juvenilefree in soil

II Stage juvenilesemerge from cyst

II Stage juvenile ineggs inside browncyst overwinteringin soil

Female cystfilled witheggs stillattachedto root

Female layseggs ingelatinousMass

Root surface

II Stagejuvenilesemergefrom eggs Female begins

to produce eggs

Male leavesroot

Females at variousstages of developmentattached to root

II Stage juvenilesattack young roots

2ndmolt

3rdmolt

4th molt

Disease cycle of the soybean cyst nematode Heterodera glycines

Late II stage juvenilesfeeding on giant cells.Root begins to form gall

Late III stage juveniles IV Stage juveniles

Adult nematodes.

Male leaves root

Old galls may containmany egg-laying femalesand new infections

Female layseggs intoegg sac

Egg sac

Galls at variousstages ofdevelopmenton roots ofinfectedplant

Small galls appearon recently infectedroots

II Stage juvenilesinvade rootletand cause formationof giant cells

II Stagejuvenilesattack rootlets

Emerging II Stagejuveniles infect new roots

II Stage juvenilefree in soil

II Stagejuvenile I Stage

juvenile Egg

1st molt

2ndmolt

3rd molt4th molt

Disease cycle of root knot caused by nematodes of the genus Meloidogyne

PARASITIC CYCLE OF CYST NEMATODE

J2 - roots through the

epidermis and migrate

through cortex

Causes cellular

damage and necrosis .

Penetrating the

endodermis

Pierce the wall of a

procambial cell

Inject secretio

nsFeeding site

Syncytium-

incorporate>200

cells

B C

(A) A female SCN laying eggs. B) Portion of soybean root with several SCN females feeding on it. (C) A flask-shaped female and a worm-like male SCN.

A

PARASITIC CYCLE OF ROOT-KNOTNEMATODE

J2 - attracted to the zone of

elongation.

Penetrate the root and migrate

intercellularly in the cortical tissue.

Migrate up the center of the root

to the zone of

differentiation

In response to signals from the nematode, procambial cells adjacent to the head of the

nematode develop into "giant cells.

Mechanical force and enzymatic

secretions .

Stages in the life cycle of the root-knot nematode. (A) Nematode egg with second-stage juvenile ready to hatch. (B) Second-stage juvenile penetrating root tissues. (C) Female root-knot nematode in plant root causing the formation of and feeding on “giant cells.” (D) Longitudinal section of Meloidogyne female feeding on giant cells. (E) Root-knot female laying eggs outside the root.

A

B

C

D

E

N

GC

GCGC

Giant CellsMeloidogyne

SyncytiumHeterodera

NEMATODE SPECIALIZATION FOR PARASITISM Central nervous system and complex

chemosensory organs called amphids .

Chemosensory signals -important for nematode attraction to host roots and also for the identification of appropriate sites for penetration of the host and initiation of feeding.

Plant parasitic nematodes possess two specialized structures, stylets and esophageal secretary glands-essential for parasitism.

(A) Close-up of the head of a plant parasitic nematode showing the spear or stylet.(B) Typical plant parasitic nematode.

A B

During feeding, the stylet is inserted through the cell wall without piercing the plasma membrane, which becomes invaginated around the stylet.

The nematode withdraws nutrients from the cytosol of the parasitized cell through a minute hole created in the plasma membrane at the stylet orifice.

Secretions from the esophageal glands released through the stylet contain the biochemical trigger(s) for giant cell and syncytium development as well as substances important for the initial penetration and migration.

During feeding- feeding tube- associated with the stylet, is found in the cytoplasm of the host feeding cell.

A new tube is formed each time the nematode

reinserts its stylet into a feeding cell, results in numerous feeding tubes in giant cells or syncytia.

In giant cells - endomembrane system rearranges to produce a compact membrane system around the feeding tube -function in transporting nutrients to the feeding tube for withdrawal by the parasite. 

PLANT GENES INDUCED DURING A COMPATIBLEPLANT-NEMATODE INTERACTION

Nematode infection

Complex changes in plant gene expression

Genes that encode cell-wall degrading enzymes

Host endoglucanase & polygalacturonase genes

upregulate

Putative pectin acetylesterase gene

upregulated in Arabidopsis in both syncitia and pre-giant

cell

NEMATODE INFECTION AND GENE UP-REGULATION

Metabolic pathways,

cell cycle & watertransport genes

Expression in and around feeding cells

Auxin-responsegenes induced

in the susceptible response

Expression

Arabidopsis AtSUC2 gene

(sucrose transporter)

companion cells

Expressed- Form and maintain metabolic sink

activity of syncytia but

not in giant cells

In root knot nematode orhologs of PHAN and KNOX

transcription regulators required for formation and maintenance of

meristem

Co localized in the feeding sites

Early nodulation gene ENOD40

and the cell cycle gene CCS52

Expression

Ethylene responsive element binding

protein (EREBP) that regulates defense in

host

Suppressed or Downregulated

Cell wall (CW)-modifying enzymes (endoglucanases,

pectolyticenzymes,cellulase,polygalacturonas,xylanases and expansins)- Penetration and migration.

CLAVATA3/ESR-related (CLE) peptides -

Peptide signaling- regulate feeding cell differentiation in plants.

Nuclear Localization Signals (NLS) have direct regulatory effects within the nucleus of the recipient plant cell.

ROLE OF NEMATODE SECRETIONS IN PARASITISM

Chorismate Mutase (CM)- Altered cellular metabolism

Chorismate- precursor in the biosynthesis of aromatic amino acids and chorismate derived compounds include the auxin indole-3-aceticacid (IAA) and the defense-related compound salicylic acid.

CM affect cellular partitioning of CM-derived compounds (CDCs) to influence the ‘developmental reprogramming of prefeeding cells’.

suppress lateral root formation and the development of the vascular system.

suppression of host defense -indirect

phytohormone effects, reduction in phytoalexins and salicylic acid.

Ubiquitin (UBQ)-Proteasome Pathway by UBQ, S-phase kinase-associated protein 1 (Skp-1) and RING-H2- modulates cell signaling and cell cycle by selective protein degradation and interaction with phytohormone proteins.

Several substances including root diffusate,

5-methoxy-N, N- dimethyl tryptamine oxalate and resorcinol - stimulate cellulases, superoxide dismutase and several proteases secretion.

Antibodies produced against stylet secretions induce some gene in nematode encoding a thioredoxin peroxidase -suppression of host defense.

Genes that encode Ran-binding protein in the microtubule-organizing center secreted from the potato cyst nematode G. rostochiensis.

Cell-cycle augmentation- modulate the cell cycle of feeding sites by increase stabilization of the microtubule network involved in spindle fiber formation and hamper the transition from interphase to mitosis, resulting in the apparent shunting of the M-phase observed in nematode induced syncytia.

A model of potential interactions of secreted products of phytonematode parasitism genes with host plant cells

KeyCW enzymeNLSUBQ, SKP1, RING-H2

Host proteinCLECM

Gland ampullaAmphid

Stylet

Amphid secretion

Chorismates

Proteosome

Signaltransduction

mRNAtranslation

Feedingtube

Gene Product Species in which identified

Possible Function

β-1,4 endoglucanase (cellulase)

G. rostochiensis Globodera tabacum Heterodera glycines Heterodera schachtii Meloidogyne incognita

Cell-wall degradation

Pectate lyase Meloidogyne javanica G. rostochiensis H. glycines

Cell-wall degradation

Polygalacturonase M. incognita Cell-wall degradation

Gene Product Species in which identified

Possible Function

Chorismate mutase H. glycines M. javanica G. rostochiensis

Alter auxin balance feeding cell formation

Thioredoxin peroxidase G. rostochiensis Breakdown of H2O2, protect against host defenses

Venom allergen-like protein

M. incognita H. glycines

Early parasitism

Calreticulin M. incognita Early parasitism

HOST PLANT RESISTANCE

Plants resistant- have reduced levels of reproduction.

With increasing restrictions on chemical pesticides, the role of host resistance for nematode control has grown its importance.

Plant nematode resistance genes Mi - resistance to several root-knot nematode species in tomato. - resistance is characterized by a localized

necrosis of host cells near the invading nematode .

Hypersensitive response occur at 42 hr after inoculation of roots with nematode juveniles suggests that cell penetration by the nematode’s stylet and injection of secretions intended to initiate feeding cell development elicit the response.

Resistance - lost at elevated temperatures.

H7- resistance to G. rostochiensis - necrosis of tissue around the invading

nematode. The few nematodes develop on H7 potato

plants are mostly male because of poor nutrition for the nematode .

• However, despite the initial necrosis, the feeding site begins to develop and the nematode becomes sedentary. In time, however, the feeding site becomes surrounded by necrosing tissues and eventually collapses.

Hs1pro-1 The first nematode resistance gene to be

cloned from a wild relative of sugar beet that confers resistance against Heterodera schachtii, the beet cyst nematode.

Resistance mediated - does not involve a hypersensitive response . - Nematodes die in the late J2 stage -degradation of the feeding structure (syncytium).

Gpa2- resistance against some isolates of the potato cyst nematode Globodera pallid.

Others- enzymes phenylalanine ammonia-lyase and anionic peroxidase induced resistance response to many other pathogens.

Phytoecdysteroid, 20-hydroxyecdysone (20E)- molting hormone of nematodes induced in spinach show the defensive role against plant-parasitic nematodes.

Induction of defense compounds methyl jasmonate in oats( Avena sativa ) reduced the invasion of both nematodes and increased plant mass.

A Galls and symptoms caused by the rootknot nematode on tomato.B.Soybean cultivars resistant(upper left) and susceptible to the cystnematode. C Females and cysts of a cyst nematode on the roots of its host plant. .

A

C

B

INTERACTION BETWEEN PLANT PARASITIC NEMATODES AND PLANT SECONDARY METABOLITES

Secondary metabolities- alkaloids, terpenoids and phenylpropanoids.

Phenylpropanoids - phenolic compounds, is well characterized and constitutes a potential target for the improvement of resistance against nematodes.

Resistant varieties had more phenylpropanoids than susceptible ones.

Cell walls of resistant roots - higher levels of lignin and ferulic acid esters.

Lignin - protection of the vascular bundle both constitutively and upon infection.

Ferulic acid esters in cortical cell walls - substrates for peroxidase catalyzed dimerization and cross linking of cell wall components and as initiation sites for lignification.

Higher level of these compounds in resistant varieties increase resistance against hydrolytic enzymes secreted by nematodes during the infection process.

B

C

A

(A) Damage caused to a patch of soybean plants by the soybean cyst nematode (SCN) (B) Soybean plants resistant (right) and susceptible (left) . (C) Root systems from resistant (left) and susceptible (right) plants from the field at B.

PROGRESS TOWARD UNDERSTANDING VIRULENCE IN NEMATODES

Studies on the development of virulence to Mi showed a progressive increase in virulence after prolonged selection on resistant plants, suggesting that several genes are involved by which a nematode can acquire the ability to circumvent resistance.

Increase in virulence may be due to loss of a nematode gene product could result in failure of the plant to recognize the nematode.

MODEL SYSTEMS Two models that have potential for

providing insights into plant-nematode interactions are the plant Arabidopsis thaliana and the animal Caenorhabditis elegans.

CONCLUSION

The identification of nematode genes involved in parasitism and other nematode specific processes and utilization of nematode inducible plant genes for creating new forms of durable plant resistance.

To engineer plants to express genes that are detrimental to the nematode.

To transform plants with genes encoding monoclonal antibodies or single chain antibodies (plantibodies) to specific stylet secretions or other components of the nematode in an attempt to block the establishment of a feeding site.

REFERENCES Getting to the roots of parasitism by nematodes (Eric L. Davis,

Richard S. Hussey and Thomas J. Baum) TRENDS in Parasitology Vol.20 No.3 March 2004

Plant nematode resistance genes (Valerie M Williamson). Currenft Opinion in Plant Biology 1999, 2:327–331

Inducible Flavone in oats ( Avena sativa ) Is a novel defence against plant parasitic nematode ( I.R.Soriano, R.E.Asenstorfer, O.Schmidt and I.T.Rilay).

Plant–nematode interactions(Valerie M Williamson and Cynthia A Gleason). Current Opinion in Plant Biology 2003, 6:1–7

Interactions between plant parasitic organism and plant secondary metabolites, with emphasis on phenylpropanoids in roots.( Nathalie Wuyts ).Info musa vol-15 no.1-2 June-december 2006.

Phytoecdysteroids: a novel defense against plant-parasitic nematodes (imelda r. soriano, ian t. riley, mark j. potter, and william s. bowers)

Nematode Pathogenesis and Resistance in Plants (Valerie Moroz ,Williamson and Richard S. Hussey) The Plant Cell, Vol. 8, 1735-1745, October 1996 @ 1996 American Society of Plant Physiologists.

Plant Pathology- G.N.Agrios.5th edition.

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