Download Lecture 18-19. Plant-pathogen interactions (Read p1103

Lecture 18-19. Plant-pathogen interactions
(Read p1103-1113)
-Disease is a disfunction of normal physiological processes in plants
caused by microorganisms or an abiotic factor.
-A pathogen that causes diseases is termed virulent
A pathogen that does not cause diseases is termed avirulent
-Types of pathogen based on effects:
necrotrophy: plant cells are killed
biotrophy:
plant cells remain alive
hemibiotrophy:plant cells initially alive and killed later
Types of Pathogens:
Bacteria: enter through wounds or stomata, live between plant cells.
Fungi: filamentous growth with specialized structures for penetration,
feeding in cells. Can penetrate directly into plant and move
intercellularly or through cells.
Nematodes: Microscopic segmented worms, use stylet for feeding.
Can feed on outside cells of root or burrow inside to set up feeding
relationship with one cell.
Viruses:
-Nucleic acid (+ RNA mostly) encapsulated in a protein coat
-Spread by plasmodesmata and phloem,
-biotrophys
-encode RNA replicase, cell-cell movement protein (Movement
Protein), and the coat protein
Figure 21.6
Figure 21.13
Box 21.1
Plasmodesmata
Figure 15.20 (p748-757)
Genetic incompatibility: no disease
Nonhost: host can’t support life-strategies
Nonhost resistance: structural barrier
Induced specific resistance response
Compatibility: diseases
preformed structure inadequate
can’t detect pathogen
defense response are ineffective
Preformed defense involves secondary metabolites
Preformed inhibitors:
Avenacin A-1 in oat root is highly effective against
Gaeumannomyces graminis Var. tritici, a major pathogen to
cereal.
Cause major disease to barley and wheat, but never oats.
G.g. avenae, a pathogen specialized for oats produces
detoxifying enzyme avenacinase.
Fig. 21.19
Disease resistance genes in plants
-Resistance to each race of pathogen is conferred by a single gene(R)
-Multiple resistance genes can be found in various cultivars or in one
cultivar, each conferring resistance to a different race.
Flor’s Gene-for-gene model
-Avirulent pathogens have product (from avirulence gene)
which is recognized by the Resistance gene in the plant.
-Each avirulence gene has a corresponding resistance gene
which recognizes it and triggers a defense reaction
-so vertical resistance a recognition reaction which triggers
general defenses of the plant.
Fig. 21.28
Only a few avirulence genes are known
NLS
Protein such as the AvrBs3 (bacteria)
vs Bs3 (pepper plants)
Bacterial elicitor syringolide (avrD)
vs. Rpg4 (soybean)
Avr9 (fungal) vs Cf 9 (tomato)
TMV replicase (viral)
vs N (tobacco)
Identify mutations in N gene
N-gene only functions
at 25oC or below
box 21.4A
Cloning R (resistance) genes
gene
structure
plant
resistance to pathogen
HM1
toxin reductase
corn
fungus H. carbonum
(toxin resistance)
fungus C. fulvum
fungus- flax rust
bacteria P. syringae
bacteria P. syringae
bacteria P. syringae
bacteria X. oryzae
bacteria X. oryzae
Tobacco Mosaic Virus
fugus F. oxysporum
Powdery mildew
Nematode
Cf-9 eLRR-TM
L6
TIR-NBS-LRR
PTO
Kinase
RPS2 LZ-NBS-LRR
RPS4 TIR-NBS-LRR
Xa21 LRR, Kinase
Xa1
NBS-LRR
N
TIR-NBS-LRR
I2C
NBS-LRR
Rpp5 TIR-NBS-LRR
Hs1pro-1controversial
Table 21. 2
tomato
flax
tomato
Arabidopsis
Arabidopsis
Rice
Rice
tobacco
tomato
Arabidopsis
sugar beet
Fig. 21.26
LRR structure
LRR: mediate protein-protein (receptor-ligand) interactions
Fig. 21.27
Read: 1131-1147
Figure 21.34
ROS (reactive oxygen species) is the first response detected in HR
ROS: superoxide (O2-) and hydrogen peroxide (H2O2)
NADPH oxidase
peroxidase
1. Directly toxic to pathogen
2. Reinforce cell walls
3. Changes in redox state of the cells
Activated response can result in HR (Hypersensitive Response)
Rapid (within 24 hr)and localized programmed cell death,
triggered in and around the site of infection by some
pathogen, further blocking the the spread of infection
Figure 20.47 (p1087-1099)
NO is required for the HR response
L-NNA and PBITU
inhibitors of
NO production
Fig. 21.38
HR
Chlorotic reaction
PR (pathogen-related) protein induction
Family
PR-1
PR-2
PR-3
PR-4
PR-5
PR-6
PR-7
PR-8
PR-9
PR-10
PR-11
PR-12
PR-13
PR-14
Type
Tobacco
tobacco
tobacco
Tobacco
Tabacco
Tomato
Tomato
Cucumber
Tobacco
Parsley
Tobacco
Member
Properties
PR-1a
Antifungal
PR-2
b-glucanase
P,Q
Chitinase
R
Antifungal
S
Antifungal
Inhibitor I
Proteinase inhibitor
P69
Endoproteinase
chitinase
Chitinase
lignin-forming Peroxidase
PR-1
Ribonuclease-like
chitinase (V) Chitinase
DEFENSIN
Antifungal
Thionins
Antifungal
Lipid-transfer proteins
Antifungal
Figure 21.44
Defenseness1
Figure 21.52
WT
Phytoalexin
PAL: phenylalanine ammonia lyase
Phenyl propanoid pathway
Phenylalanine is diverted to the synthesis of flavonoid phytoalexin
CHS: Chalcone synthase
First enzyme in flavonoid pathway
Let to the synthesis of phytoalexin:isoflavonoids
Secondary
&
primary infection
Figure 21.48 TMV-N-gene mediated SAR
Figure 21.50 Genetic dissection of SAR pathway
Necrotic
pathogen
infection
Systemic
Signal
(phloemmobile)
SA
CPR1
NPR1
NahG
SAR
Gene
expression
NPR1: has ankyrin repeat, similar to IkB
NF-kB/IkB
NahG: salicylate hydroxylase, which converts SA to catechol
Figure 17.80
Resistance
Gene silencing
Plants: PTGS (post transcriptional gene silencing)
Fungi (neurospora crassa): Quelling
Animals: RNAi (RNA interference)
1. Avr and R genes used in combination to promote acquired resistance
2. Over and constitutively expressing defense regulators: NPR, Prf
3. Over-expression of specific defense genes:
Chitinase, glucanase, phytoalexin, PI, lectin
4. Engineer plants to constitutively produce a key defense signal.
5. Eliminate a gene product absolutely required for microbial pathogenesis
6. Over expression of non-plant genes that have antimicrobial functions
7. Over-expression virus protein CP or MP
8. Express antibody against pathogen
Read 1147-1155
Fig. 21.55
Fig. 21. 56
A.
Expressing stilbene
synthase in tobacco
phytoalexin resveratrol
confering resistance
to the Botrytis cinerea fungi
G: Glucanase
C: Chitinase
Cercospora nicotianae (fungus)
D. antisense to glucanase
expressed in tobacco exhibit
enhanced resistance to TMV
C. glucose oxidase gene from
Aspergillus niger confer these
potato plants resistant to
fungal pathogen
Verticillium dahliae
Ornithine carbamyl-transferase
(OCTase): an bacterial-derived
toxin-inactivation enzyme.
over-expression of TMV CP
Over expression of TMV MP
Fig. 21.57
cryI: highly specific to species of moths and butterfly
cryII: various lepidoptera (butterfly), diptera (fly)
and coleoptera (beetles)
cryIII: coleoptera
cryIV: diptera
All products of single gene
Simple structure and genetics
Highly specific to particular groups of insects, kill only
Larvae. Not toxic to human and other non-target
organisms
Biodegradable
Fig. 21.59 BT (Bacillus thuringiensis) toxin
are important tools against insect pests
BT crops are commercialized in 1996
cotton, maize, and potato(Russet Burbank, NewLeafTM)
Fig. 21.60
Antibody production against viral proteins
artichkoke mottle crinkle virus (AMC)
BENEFIT OF GMO CROP
Growers don’t depend on weather to spray
Savings made on insecticide expenditure, labor & equipment
Improvement for environment because less insecticide will be sprayed,
no spray drift
Contamination of ground water arround farm land will be reduced
Deleterious effects on beneficial insects will be alleviated,
thus, more effective biological control of the pest insect
Other non-target organisms from bees and earth worms to birds and human
will not be exposed
Concerns
Potential development of resistance by insects to the toxin