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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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