4. Host factors that affect development of
epidemics
Level of Genetic Resistance or Susceptibility of
host
Degree of Genetic uniformity of host plants
Type of crop
Age of host plants
4
5. Host Defense Mechanisms
1. Basal resistance
Recognition of microbe-associated molecular patterns
(MAMPs), such as bacterial flagellin
5
8. Life span of the plant
Susceptibility
Growth period Adult period
3. Age related resistance (ARR)
8
(Change of susceptibility of plant parts with age)
9. Effect of Crop age rate of infection
Cassava planting of different ages exposed to African Cassava mosaic geminivirus
show increased resistance to infection as they age.
9
10. Age Related Resistance
Increase or acquisition of resistance to pathogenic infections
as a function of plant development.
Eg: rice/Pyricularia oryzae &
rice/Xanthomonas compestris pv oryzae
Syn: ontogenic resistance, developmental resistance, mature
seedling resistance, adult seedling resistance.
10
11. Positive correlation between increasing plant age & glyceollin
production - Phytophthora megasperma var. sojae (Soybean)
Cotton phytoalexin in response to Verticillium albo-atrum
Constitutive accumulation of terpenoids in cotton
Capsidol- phytophthora capsici
Toxic compounds
Defense associated compounds
- In tobacco PR proteins – PR1, PR2 & PR3 against virus &
fungal pathogens
- Salicylic acid in Tobacco & Arabidopsis
ARR mechanisms will differ with crop/pathogen interaction
11
12. Age-related Resistance in Arabidopsis Is a
Developmentally Regulated Defense Response to
Pseudomonas syringae
• Arabidopsis thaliana ecotype Colombia (Col-0), mutants npr1-
1, etr1-4,pad3-1, eds7-1, sid1 and sid2 & transgenic NahG line
• Avirulent & virulent strain of Pseudomonas syringae pv
tomato (Pst) strain DC3000 & P. maculicola(Psm) strain 4326
Julianne et al. (2002) The Plant Cell
12
13. Col-0 plant leaves 8 & 16 were inoculated with Pst @ 106
cfu/mL from 26-57 dag at 1 wk internal
Old plants become more resistant to Pst i.e. 10 fold reduction
in bacterial growth between 30 & 40 dag.
There was no significant difference in leaf 8 & 16 bacterial
levels- differences in leaf morphology do not affect ARR
50 dag
13
14. Defective for SAR
More susceptible
Accumulates very less
Camalexin, wild type
Susceptible to Pst &
Psm, Wild type to SAR
Defective in ethylene
signaling & ISR ARR is not require ethylene signaling & not an ISR response to PGPR
SAR not requires to ARR
No effect on ARR
In Planta Bacterial Growth In Young and Mature
Arabidopsis Mutants
14
15. Then which factor is responsible ?...
• Transgenic NahG & mutant sid1 and sid2 plants (accumulate
little SA) were tested to determine whether SA accumulation
is required for ARR response.
Both sid1 & sid2 supported
vigorous in planta bacterial
growth in young & mature plants
in a manner similar to NahG,
unlike wild-type Col-0.
SA accumulation is required for ARR
15
16. Accumulation of SA act as a signaling molecule, stimulating
the production and secretion of heat stable anti-microbial
compound(s) into the intercellular space
Antimicrobial activity was detected only in IWFs from mature
plants inoculated with Pst, not in IWF from mature mock-
inoculated plants
ARR is developmentally regulated and pathogen induced
response in Arabidopsis.
16
17. Stress induces an ARR-Like responses in young plants
Mild nutrient limitation can
affect the level of in planta
growth of Pst.
In young rice, wounding of one
leaf induces accumulation of
Jasmonate & local activation of
PR genes. This is correlated with
ISR to subsequent blast disease.
Mild drought- reduced in planta
bacterial growth (2-6 fold)
compared to control plants of
same age
Constantly wet soil sometimes
supports algal growth & that
plants grown under these
conditions exhibit reduced
growth of Pst.
17
18. Forms of ARR
1. Resistance & developmental transition
2. Resistance & tissue maturity
3. Increased or acquired resistance & plant development
4. specific & broad spectrum resistance
In Turnip and Arabidopsis, the long-distance movement of
CaMV is influenced by the developmental stage of the
invaded leaves & progressively more restricted to basal
portion of lamina during growth
18
20. 1. Resistance & developmental transition
Postembryonic /vegetative in
Arabidopsis
Col-O ecotype develop resistance
in true leaves against DM fungi
but not so in Ws-O ecotype (it
lacks RPP31)
Juvenile/adult transition during vegetative growth
In maize Corngrass1 mutant (Cgm1), the juvenile-vegetative
phase is extended & adult resistance to common rust (Puccinia
sorghi) is delayed. There fore expression of adult characteristics
are necessary for leaf resistance.
In Cabbage adult stage is resistant to DM than cotyledony stage
20
21. Cont…
Correlation between floral transition & resistance
Arabidopsis resistance to CaMV & Pseudomonas syringae.
Confirmed by terminal flower 1 (tfm) mutant. (TFL1 Protein
floral induction & maintenance of floral identity in apical
meristem)
PR1 & PR2 are specifically expressed in tobacco floral tissue
Resistance may correlated with senescence.
(Not so in Arabidopsis/Pst to SAG13)
21
22. Developmentally regulated mechanisms affect the
ability of a fungal pathogen to infect and colonize
tobacco leaves
Karine Hogot et al. (1999), The Plant Journal, 20(2)
Vegetative phase Flowering phase
Control infection effectiveness
(intercellular fluid, not SA)
Restriction of fungal hyphae expansion
(PR1 & SA accumulation)
Material & methods:
Nicotiana tabacum cv Xanthi nc., transgenic lines NahG-8 & NahG-9 expressing
or not expressing NahG genes (codes for Salicylate dehydrogenase, converts SA
to catechol)
Phytophthora parasitica isolate 329, infiltrated 50µl of suspension (100
zoospores)
22
23. Tobacco plants begin to express developmental
resistance at 75-85 das
An average of 60% of the inoculated zones showed disease symptoms,
but spreading was reduced by 80%
not only control of fungal hyphae expansion but also decrease in
infection efficiency during flowering phase
23
24. SA-dependent & SA-independent mechanisms
Expression of mechanisms which lead to control of fungal devt.
after floral transition require SA accumulation.
Increase in inoculated zones without any symptoms of diseases in
NahG-8 shows, induction of events that affect the ability of fungus
to infect leaf tissue do not require SA accumulation
24
25. Acquired resistance during development & apoplastic
PR1 protein accumulation
Establishment of SAR leads to systemic
transcriptional activation of a subset of PRs
genes
Immunoblotting expt’s were undertaken
to study accumulation of PR1 protein in
apoplasm during plant devt.
Xanthi nc plants were treated with cryptgein
to induce SAR. (induced PR proteins)
PR1 Protein expression was correlated with the ability of tobacco to inhibit the
fungal devt. in planta rather than infection effectiveness during flowering
IFs (Hammond-Kosak)- Protein extract
15% SDS-PAGE electrophoresis
Incubate Nitrocellulose membrane
with IgG antibody
Goat peroxidase cojugated IgG
Detection system (Amersham)
25
26. Which controls Infection effectiveness during
flowering ?
• Intercellular fluid (cytotoxic activity)
Survived cells
germinated cells::::
The influence of Ifs on in vitro
germination of zoospores
Zoospores (5x105) were
incubated for 2 h in the presence
of different IFs
Cytotoxic activity on fungal cells
was not detected in IFs from
cryptgein treated Xanthi plants.
The expression of an in vitro
cytotoxic activity on fungal cells
in IFs is from plant committed to
flowering
26
27. 2. Resistance & Tissue maturity
• Several plant species develop resistance that is restricted to a
given tissue or organ, as a function of maturity.
• Soybean: Resistance to Phytoophthora sojae in hypocotyl
varies with tissue maturity.
• Apple tree: Leaf maturity is positively correlated with
resistance to Venturia inequalis
• Maize: During vegetative growth, leaves with juvenile traits
are susceptible & leaves with adult traits are resistant (>8th
node) to Puccinia sorghi
• Rice: Leaf maturity has no effect on the degree of resistance
to Xanthomonas compestris pv. oryzae, where as leaf rank
does have an effect.
27
28. Effect of Age & Leaf Maturity On the Quantitative Resistance of
Rice Cultivars to Xanthomonas campestris Pv,oryzae
• Materials: Cisadane, BR51-282-8(BR51), IR28, IR40 are
moderately resistant.
• TN1 & IR9101-46 (9101)- susceptible checks
• Xanthomonas campestris ov. oryzae race2 strain PXO86 &
race6 strain PXO99 (1 X 109 cfu/ml)
} Largest decrease
in lesion length
(cm)
Koch et al. (1991), American Phytopath. Soc. 28
29. Cont…
Decrease in lesion
length was less evident
after maximum tillering,
but flag leaves were
more resistant than
leaves at booting stage
No significant age X cultivar interaction was found
Plant age does not greatly affect our ability to distinguish among
intermediately resistant cultivars
Difference in lesion length between immature and mature leaves
was similar in all cultivars
Screening for quantitative resistance to X.c. oryzae can be done at
all stages of growth
29
31. 4a. Developmental effect on Specific resistance
• ARR may be effective against several pathogens, a particular
pathovar, strain or race of pathogen
Crop Gene(s) Pathogen
Rice Xa6 X. Campestris pv. oryzae
Xa21 X. oyzae pv. oryzae
Wheat Lr gene fam. (few) P. recondita f.sp. tritici
Sr gene fam. (few) P. graminis f.pv. Tritici
Tomato Hcr9-9A, Hcr9-9B,
Hcr9-9th
Cladosporium falvum
Maize Cg1 Puccinia sorghi
31
32. Developmental control of Xa21-mediated
disease resistance in rice
Reproducible means of infecting plants
at full leaf expansion
Xa21-resistance progressively increases
from the susceptible juvenile leaf 2
stage.
Resistance (%)= 1 Xa21 line mean lesion length
susceptible line lesion length
- X 100
32
33. Cont..
Xa21 expression is independent of plant
developmental stage, infection with
Xoo, or wounding
Expression of the Xa21 gene transcript is
not correlated with expression of Xa21
disease resistance
Developmental regulation of Xa21-resistance is either controlled
post-transcriptionally or by other factors
XA21 has an intracellular serine–threonine kinase domain, it is
a likely possibility that XA21 activity is controlled by
phosphorylation status
Rice Xa21 binding protein 3 is a ubiquitin ligase (HB3) required
for full Xa21-mediated disease resistance
33
34. 4b. Developmental effect on Broad spectrum
resistance
Flowering growth in tobacco: express resistance to
Peranospora tabacina, Phytophthora parasitica & TMV
Mature Arabidopsis: Pseudomonas syringae pv. tomato and
pv. maculicola as well as Hyaloperanospora parasitica
After onset of berry ripening in grape: express resistance to 3
ascomycetes
Control of viral migration (CaMV) in Turnip & Arabidopsis.
34
35. Genetic Analysis of Developmentally Regulated
Resistance to DM (Hyaloperonospora parasitica) in
Arabidopsis thaliana
ARR to H. parasitica Emco5
is activated in true leaves
of Arabidopsis Col-O but
not Ws-O:
Ws-O is highly susceptible
to Emco5 throughout the
devt., in contrast to Col-O
(shows delayed HR)
McDowell et al. (2005), American Phytopath. Soc.
S-Sporangiospore, O-oospore,TN- Trailing necrosis,
H-hyphae
35
36. Adult resistance in Col-O is race-specific & is suppressed by
defense signal transduction mutants
Adult Col-O plants are susceptible to H.
parasitica isolate Noco2 & Ahco2
Trailing necrosis/HR & H2O2 production in
true leaves indicates, it is results from active
defense response of host
Each of isogenic Col lines is deficient in SA-
mediated signaling their by impairing basal
resistance, SAR & certain R genes
Adult resistance in Col-O requires variety of
regulatory components previously associated
with inducible defense
36
37. Genetic analysis of Adult resistance
Phenotypes in F1 indicates susceptibility is incompletely
dominant over resistance.
F2 segregation ratio: 24% Col-like adult resistance (1):76%
full/intermediate susceptible (3)- indicates single recessive
gene controls
Segregation of adult resistance to Hyaloperanospora parasitica Emco5
Cross F1 F2
Sus Int Res Res
rpm1-3 (Col- 5) x Ws-O 0 8 1 30 89 1.09 (P>0.3)
Col-O X Ws-O 0 6 3
Ws-O X Col-O 0 2 4
37
38. Recessivity of resistance in Col-O x Ws-O hybrid could be a
gene-dosage effect !
XWs-O (2x) Col (CS3151, CS3432-4x)
F1 (3x) Col/Col/Ws-O Susceptible
But supported less sporulation than Ws-O parent & diploid F1
Ws-O susceptibility phenotype is incompletely dominant to
adult resistance in Col-O.
Genetic mapping in a Col x Ws F2 population revealed a major
locus on the bottom arm of the chromosome 5, named as
RPP31
38
40. Cont…
Crop Developmental
control
Response Pathogen
Tobacco Flowering
PR1a,PR2
Chitinase, ß- (1-3) glucanase,
peroxidase
TMV
Peranospora
tabacina
Grape Berry ripening Chitinase, PR5, LTP U. necator
Hordeum
vulgare
Embryo developing
Before grain
desiccation
9-LOX (Lipoxigenase) pathway
PR
Pathogens
Developmental resistance also involves up-regulation of gene
involved in modification /strengthening of cell wall along with
defense genes
40
41. Defense mechanisms in Arabidopsis
• SA has antimicrobial activity & partially rescues the iap1-1
ARR defect.
41
Suggesting iap1-1 lies up-stream
of SA accumulation in ARR pathway.
Prediction: iap1-1 accumulates little
intercellular SA.
Leaves of 5 wk old plants inoculated with Pst
at 5 & 24 h post infiltration
Level of SA in Pst or mock inoculated mature plants
measured by Gas chromatography-mass spectrometry
42. Cont…
Addition of SA in the intercellular space of eds1-1 plants did not
result in the rescue of the eds1-1 ARR defect. EDS1-1 at down-
stream of SA
Combining microarray analysis with reverse genetics using T-DNA
insertion lines, 4 additional genes were identified, UGT85A1,
CDA1, ANAC055 and ANAC092
42
iap1-1
Salicylic acid
eds1-1
UGT85A1, CDA1, ANAC055 and ANAC092
Defense to infection
Carviel, J. L., et al.,2009, Mol. Plant Path., 10(5): 621-634
43. PR proteins (PR3, PR5, nsLTP) are express constitutively at low
level in cells and accumulate in response to fungal attack or
inducers of acquired resistance with the exception to reproductive
organs (developmentally regulated expression).
43
44. A. Pattern of protein accumulation
in grape berry during ripening.
B. Comparison of total protein
profile of susceptible Vs
resistant variety to Botrytis
cinerea
Developmental accumulation of antifungal proteins like – thoumatin like protein
(GO), chitinase (CBC & AC forms) & ns LTP and hexoses in grape berry provide
resistance against Guignardia bidwellii (fruit rot) & Botrytis cinerea
GO
nsLTP
AC
CBC
44
45. 45
Sugar molecules may act as a signal molecule to regulate the
expression of antifungal proteins genes during fruit ripening.
Sugar repress genes which codes for C-assimilatory enzymes
Up-regulates genes for protease inhibitors, chalcone
synthase, PR3, PR1b & PR-Q
Sugar and antifungal proteins interact to mediate host plant
defense against phytopathogens either by
Disruption of fungal gene regulation by sugar repression
Solute mediated preservation of native protein structure (CBC, GO)
46. Relationship between defense & development
in plants
Expression of resistance to disease during host devt.
Involvement of plant hormones in devt. & P-P interaction
Eg: SA, JA, Ethylene, ABA
Molecular conservation of transduction pathways governing
various process
Eg: Arabidopsis- In csa1 mutant TIR-NBS-LRR protein involved
in photomorphogenic devt. is complemented by RPS4
(homologue of TIR-NBS-LRR confers resistance to Pst)
Tobacco transcription factors of the TGA family: TGA2.1- SA
inducible gene expression & TGA 2.2- regulatory role in
correct stamen devt.
46
