Gpb minor seminor

ICAR-INDIAN AGRICULTURAL
RESEARCH INSTITUTE
DIVISION OF PLANT PATHOLOGY
“Plant genes hijackedby necrotrophic fungal pathogens”
Credit seminar in Division of Genetics
GP691-2018
Seminar leader: Dr. Shailendra Jha
Chairperson: Dr. T. Prameela Devi
Speaker: Chaithra, M.
11580
PhD 1st year

FLOW OF SEMINAR…….
Introduction
Brief review of PTS, PTI,ETI and ETS
Mode for signaling events of plant-pathogenic interaction
Necrotrophic effectors
Classic gene for gene model v/s inverse gene for gene model
Different NEs gene-necrotrophic sensitivity gene interactions
Case studies
Conclusion

3Plant genes hijacked by necrotrophic fungal pathogens , 11580; 2019-2020, IARI, New Delhi
INTRODUCTION
Types of plant pathogenic fungi (based on life cycle of pathogens)
Biotrophic Fungi Necrotrophic Fungi Hemibiotrophic Fungi
Ex: Erysiphe, Ustilago,
DM fungi, Rust fungi,
Cladosporium etc.,
Ex : Rhizoctonia, Pythium,
Alternaria, Botrytis,
Sclerotium etc.,
Ex: Phytophthora,
Pyricularia, Colletotrichum,
Bipolaris etc.,

Pathogen Infection and Host Defence: Continuous battlePAMP Triggered Immunity (PTI)
Effector Triggered Susceptibility (ETS)
Effector Triggered Immunity (ETI)
Pathogen
PAMP
Effector
(Avr)
PTI ETS ETI
Avr-R
Effector
(Avr)
Avr-R
ETS ETI
AmplitudeofDefence
High
Low
Threshold for HR
Threshold for
Effective
resistancePAMP-PRR

Bent and Mackey, 2007
Model for the signaling events in plant-biotroph interactionsModel for the signaling events in plant-necrotroph interactions

Plant genes hijacked by necrotrophic fungal pathogens , 11580; 2019-2020, IARI, New Delhi
• NE: Host specific toxin (HST)
• NE: cell-wall degrading enzymes, proteins, or secondary metabolites
• Almost all NE produced from Dothideomycetes class of fungi
• Production of NE recognized by specific dominant host genes known as
NE sensitivity gene. Which leading to plant-induced cell death along with
other hallmarks of a ‘resistance’ response (upregulation of defense
response genes, an oxidative burst, and MAP-kinase signaling etc.,)
Necrotrophic effectors (NE)
Plant Pathogen
Species Gene class location species NE/toxi
n
structure Comparitive
ineraction
Zea mays
(Maize)
T-urf13 unique Mitochondrial
plasmamembrane
Cochilobolus
heterostrophus
T-toxin Linear
polyketide
Distruption of mt
activity
Arabidopsis
thaliana
LOV1 NLB cytoplasma Cochilobololus victorae Victorin Cyclic
pentapptid
e
Induction of host
program cell death and
defense response
Sorghum bicolor
(Sorghum)
Pc NLB cytoplasma Periconia circinata PC-toxin Peptidyl
chlorinated
polyketide
Induction of host
defense response
Triticum
aestivum
(wheat)
Tsn1 PK-
NLR
cytoplasma Parastagonospora
nodorum, Pyrenophora
tritici repents, Bipolaris
sorokiniana
SnToxA,
PtrTox,
BsToxA,
13.2 kDa
protein
Induction of host
defense response
Triticum
aestivum
(wheat)
Snn1 WAK Plasmamembrane Parastagonospora
nodorum
SnTox1 10.3 kDa
protein
Induction of host
defense response
Table: 1. Plant genes and the pathogen molecules they interact with to confer susceptibility to necrotrophic pathogens
Faris and Friesen, 2020
6

Classical gene for gene model v/s Inverse gene for gene model
Classical gene for gene Model
• Biotrophic plant–pathogen
interactions.
• The direct and indirect interaction
between the host (R) and pathogen
(Avr) components leads to disease
resistance. (effector-triggered
immunity).
• Incompatible interaction between Avr
and R= Resistance reaction.
Inverse gene for gene model
• Necrotrophic plant-pathogen
interaction
• The direct and indirect interaction
between the host (S) and pathogen
(NE) components leads to disease
susceptibility. (effector-triggered
susceptibility).
• Compatible interaction between S and
NE= susceptable reaction.
Friesen and Faris, 2010

 T-Toxin : by Race T isolates of Cochliobolus heterostrophus (southern corn leaf
blight (SCLB) in maize).
 T-toxin binds to the URF13 product of the T-urf13 gene which were assembled in the
cms-T mitochondrial plasma membrane of maize plant.
 Pore formation and permeabilization of the inner mitochondrial membrane, which then
lead to effectively inhibiting malate dehydrogenase activity of infected host plant.
1. T-urf13-T-Toxin

2. LOV1-victorin
 Victorin: produced by Cochliobolus victoriae (Victoria blight of oats).
 Sensitivity to victorin is conferred by a single dominant gene in oat called Vb.
 The Vb locus is thought to be the same locus as Pc-2, which confers resistance to oat
crown rust caused by Puccinia coronata f. sp. avenae.
 In Arabidopsis by cloning Vb gene identified the victorin sensitivity gene: Locus
Orchestrating Victorin effects 1 (LOV1),
 LOV1 is a member of the RPP8 family of proteins ( R gene): induction of the
pathogenicity gene PR-1 and the production of camalexin (disease resistance).
 LOV1 : which encodes a coiled-coil, nucleotide binding, leucine-rich repeat (NLR)
protein.
 LOV1 does not bind victorin directly but instead acts as a guard of the thioredoxin
TRX-h5 which is targeted for direct binding by victorin. LOV1 “guards” the defense
thioredoxin, TRX-h5 (guardee). Sweat and Wolpert, 2007

PC-toxin (peritoxins): Produced by Periconia circinata cause milo disease in
sorghum.
PC-toxin sensitivity is conferred by Pc.
Compatible Pc–PC-toxin interactions lead to hallmarks of programmed cell death and
defense including inhibition of mitosis, condensed chromatin, electrolyte leakage,
potassium ion flux, and other disruption in cell development and function reminiscent
of a defense response.
3. Pc–PC-toxin

 ToxA: First proteinaceous HST to be discovered in any pathosystem and was first
identified and purified from the tan spot fungus, Pyrenophora tritici-repentis: Ptr
ToxA.
 ToxA gene transferred from Parastagonospora nodorum (SnToxA) (septoria nodorum
blotch (SNB) in wheat) to P. tritici-repentis by Lateral gene transfer mechanism.
 ToxA gene was also identified in isolates of Bipolaris sorokiniana (spot blotch in
wheat).
 NE behaviour of ToxA is conferred by Tsn1.
 Tsn1: encodes a protein with serine/threonine protein kinase (PK) and NLR domains
all in the same open reading frame.
4. Tsn1–ToxA

ToxA does not interact directly with the Tsn1 protein.
ToxA interact chloroplast-localized protein called ToxABP1, plastocyanin and
pathogenesis-related protein 1 (PR-1).
The expression of Tsn1 is regulated by light.
In P. nodorum pathogen produced more number of HST genes viz., SnToxA, SnTox1,
SnTox2, SnTox3 and SnTox4.
Toxin Host gene Markers Maximum disease
significance
Host gene
chromosome
arm location
Reference
SnToxA Tsn1 Xfcp1, Xfcp2, Xfcp394,
Xfcp620
95% 5BL Friesen et al. (2006)
Liu et al. (2006)
Friesen et al. (2009)
Zhang et al. (2009)
Faris and Friesen (2009)
SnTox1 Snn1 Xfcp618, Xpsp3000 58% 1BS Liu et al. (2004a),
Liu et al. (2004b),
Reddy et al. (2008)
SnTox2 Snn2 XTC253803, Xcfd51 47% 2DS Friesen et al. (2007),
Friesen et al. (2009),
Zhang et al. (2009)
SnTox3 Snn3 Xcfd20 18% 5BS Friesen et al. (2007),
Liu et al. (2009)
SnTox4 Snn4 XBG26267, XBG262975,
Xcfd58
41% 1AS Abeysekara et al. (2009)
Friesen and Faris, 2010
Table 2: Stagonospora nodorum produced different HST and their respective host (wheat) gene.

Plant genes hijacked by necrotrophic fungal pathogens , 11580; 2019-2020, IARI, New Delhi
• First HST–host interaction to be described in the wheat–SNB system.
• Sensitivity to SnTox1 is conferred by the wheat gene Snn1.
• Snn1: member of the wall-associated kinase (WAK) class of receptor kinase genes.
• Snn1 domains: membrane-spanning proteins with intra-cellular protein kinase domains
and extracellular galac-turonan binding (GUB_WAK) and epidermal growth factor-
calcium binding (EGF_CA) domains.
• SnToxA–Tsn1, SnTox1–Snn1, SnTox2–Snn2 and SnTox4–Snn4 : all four interactions
were light dependent.
5. Snn1–SnTox1
13

McDonald and Solomon, 2018Faris and Friesen, 2020

 Map-based cloning of the Tsn1 gene.
 Chromosome Walking and Identification of Tsn1 Candidate Genes.
 Validation and Structural Characterization of Tsn1.
 Comparative Analysis of Tsn1 candidate genes.
 Transcriptional regulation of Tsn1 gene.
 Type of ToxA-Tsn1 Protein Interaction.
Faris et al., 2010
Case study-1

Map-based cloning of the Tsn1 gene
Fig. 1: A) Genomic region of Tsn1 gene(red); B)Genetic linkage map of the Tsn1 region on 5B-L chromosome of
wheat; C) BAC-based physical maps of the Tsn1 region anchored to the genetic map; D) Predicted candidate genes
(oval shape) and markers (names beginning with an “X”); E) Exons (purple) and UTRs (gray) of Tsn1 gene.

Amplification of full length c-DNA Tsn1 by using primers located at the 5′ end of the
translation start site and the 3′ end of the stop codon of LDN (Langdon): to verify that the
S/TPK and NBS-LRR domains are encoded by a single transcript.
Validation and Structural Characterization of Tsn1
10,581 bp
4,473 bp
161bp 391 bp
: Exons : UTR
Fig. 3: Southern hybridization (Restriction enzyme: Xbal and Probed: FCG34 (NBS
region of Tsn1) and PCR analysis (primers for marker Xfcp623(Tsn1) (intron five of
Tsn1) of 24 selected wheat lines.
Fig. 2: Structural characterization of Tsn1 region of LDN
Table. 3: Description of induced and natural mutations identified with the Tsn1 gene
Fig. 3: Leaves of Kulm (Tsn1) (A and C) and Kems103 (Tsn1 mutant) (B and D)
inoculated with S. nodorum (A and B) and infiltrated with ToxA (C and D).

Fig. 4: A) Colinearity of genes within the Tsn1 region; B) Comparisons of the Tsn1 domains
• At the amino acid level,
the S/TPK and NBS-LRR
portions of Tsn1 are most
similar to rice homologs
• The separate S/TPK and
NBS domain of Tsn1 is
closely related to R gene
of barley stem rust: Rpg1
and maize rust: Rp3.

Transcriptional Regulation of Tsn1
Fig. 5: Tsn1 expression
survey by RT-PCR with
GAPDH as an endogenous
control
Fig. 7: RQ-PCR evaluation of Tsn1 expression in ToxA-challenged plants
Interaction of Tsn1 Protein with ToxA
 Yeast two-hybrid analysis
 Negative results observed between the full-length Tsn1 gene and individual S/TPK,
NBS, and LRR domains with ToxA.
 Tsn1 protein does not interact directly with ToxA
Fig. 6: Quantitative evaluation of Tsn1 gene expression by using RQ-PCR

SnToxA: Parastagonospora nodorum
+
Necrotrophic sensitivity gene: Snn1
Shi et al., 2016
Case study- 2
Septoria nodal blotch

Fig. 8: A) The genomic region of Snn1 gene on the short arm of 1B chromosome (red); B) Genetic linkage map of the
Snn1 region; C) BAC based physical map of the Snn1 region anchored to the genetic linkage map; D) Genetic linkage
mapping of the seven candidate genes identified in the four BACs from the candidate gene region in (C).
Fig. 9: Gene structure of the TaWAK (Snn1) gene
: Exon; : Introns
Map-based cloning of the Snn1 gene.

Validation of Snn1 by mutagenesis and transgenesis
Ethylmethane sulfonate (EMS) treatment : Seeds of the SnTox1-sensitive wheat landrace Chinese spring
(CS)
Fig. 10: Infiltration and inoculation reactions on leaves of wild-
type CS and the EMS mutant CSems6125
Fig. 11: C) Reactions to SnTox1 infiltrations of CS (Snn1+), untransformed
Bobwhite (BW; Snn1−), and sensitive and insensitive T1 transgenic plants both
derived from the same event (BW5240). D) Transgenic plants that were sensitive
to SnTox1 were also susceptible to disease caused by spores of an SnTox1-
producing fungal isolate
Fig. 12: E)All SnTox1-sensitive T1 plants derived from event BW5240 had
the TaWAK transgene, and all insensitive plants lacked the transgene.
F) Similarly, all SnTox1-sensitive BW5240 T1 plants expressed TaWAK,
whereas the insensitive plants did not

Transcriptional regulation of Snn1
Fig. 13: Snn1 expression survey in CS by RT-PCR with GAPDH as an endogenous control
Fig. 14: Quantitative expression of Snn1 by RQPCR B) 2-week-old plants exposure to 12-hour light/dark cycle; C) SnTox1-challenged plants

Yeast two-hybrid analysis of Snn1-SnTox1 interactions
Fig. 15: Overview of the Snn1-SnTox1 and Tsn1-SnToxA interactions

Few reports of importance of NEs to induce ETS

Few Reports of plant resistance gene hijacked by necrotrophic pathogens

 Difference in the life cycle behavior of Necrotrophic fungi: induce ETS by hijacking
the host resistance gene.
 Abolish NE recognition.
 Elimination of NE sensitivity genes is a full of potential risks. Eg: Vb/Pc-2 genes in
oat, it is possible that a gene conferring susceptibility to a necrotroph could potentially
confer resistance to a biotroph.
 Selection pressure on the pathogen to identify and subvert new host targets.

Future aspects…….
 Necrotrophic specialists harbor the ability to exploit diverse host targets to
hijack the host defense mechanisms and cause disease.
 Identities of the NE sensitivity genes in other systems and understand the
extent at which to subvert additional genes/pathways to cause disease.

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