ADVANCE CONCEPT ON HOST NEMATODE INTERACTION

1. SEMINAR ON
HOST- NEMATODE INTERACTION
VINOD UPADHYAY
M-10140
M.Sc.(Ag) Final yr.
MPP,IASc., BHU.

2. 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 .

3. • 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.

4. 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.

5. II Stage juvenile invade root
and cause formation of syncytia
IIl Stage male and female
juvenile feeding on syncytia
IV Stage juveniles
Syncytium of male
begins to degenerate
Adult nematodes
II Stage juveniles
attack young roots
II Stage juvenile
free in soil
II Stage juveniles
emerge from cyst
II Stage juvenile in
eggs inside brown
cyst overwintering
in soil
Female cyst
filled with
eggs still
attached
to root
Female lays
eggs in
gelatinous
Mass
Root surface
II Stage
juveniles
emerge
from eggs Female begins
to produce eggs
Male leaves
root
Females at various
stages of development
attached to root
II Stage juveniles
attack young roots
2nd
molt
3rd
molt
4th molt
Disease cycle of the soybean cyst nematode Heterodera glycines

6. Late II stage juveniles
feeding on giant cells.
Root begins to form gall
Late III stage juveniles IV Stage juveniles
Old galls may contain
many egg-laying females
and new infections
Female lays
eggs into
egg sac
Egg sac
Galls at various
stages of
development
on roots of
infected
plant
Small galls appear
on recently infected
roots
II Stage juveniles
invade rootlet
and cause formation
of giant cells
II Stage
juveniles
attack rootlets
Emerging II Stage
juveniles infect new roots
II Stage juvenile
free in soil
II Stage
juvenile
I Stage
juvenile
Egg
1st molt
2nd
molt
3rd molt
Disease cycle of root knot caused by nematodes of the genus Meloidogyne

7. 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
secretions
Feeding
site
Syncytium-
incorporate
>200 cells

8. 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

9. 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 .

10. 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

11. N
GC
GC
GC
Giant Cells
Meloidogyne
Syncytium
Heterodera

12. NEMATODESPECIALIZATIONFOR
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.

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

14.  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.

15.  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.

16. PLANTGENESINDUCEDDURINGACOMPATIBLE
PLANT-NEMATODEINTERACTION
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

17. NEMATODEINFECTIONANDGENEUP-REGULATION
Metabolic pathways,
cell cycle & water
transport genes
Expression in and
around feeding cells
Auxin-response
genes 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

18. 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

19.  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

20.  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.

21.  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.

22.  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 nematodeG. 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.

23. A model of potential interactions of secreted products of
phytonematode parasitism genes with host plant cells
Key
CW enzyme
NLS
UBQ, SKP1, RING-H2
Host protein
CLE
CM
Gland ampulla
Amphid
Stylet
Amphid secretion
Chorismates
Proteosome
Signal
transduction
mRNA
translation
Feeding
tube

24. 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

25. 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

26. HOSTPLANTRESISTANCE
 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 .

27.  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 .

28. • 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).

29.  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.

30. A Galls and symptoms caused by the root
knot 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

31. INTERACTIONBETWEENPLANTPARASITICNEMATODES
ANDPLANTSECONDARYMETABOLITES
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.

32.  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.

33. 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.

34. PROGRESSTOWARDUNDERSTANDING
VIRULENCEINNEMATODES
 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.

35. MODELSYSTEMS
 Two models that have potential for providing
insights into plant-nematode interactions are
the plant Arabidopsis thaliana and the animal
Caenorhabditis elegans.

36. 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.

37. REFERENCES
 Getting to the roots of parasitism by nematodes (Eric L. Davis, Richard S.
Hussey andThomas J. Baum) TRENDS in ParasitologyVol.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.

38. INVITATIONTO ALL FOR A CUP OFTEA AND SWEET