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How Magnaporthe oryzae invades rice plants? - Coggle Diagram
How Magnaporthe oryzae invades rice plants?
Trehalose-6-phosphate synthase, an
NADPH-dependent genetic switch in
M. oryzae
M. oryzae
is to
integrate
its response to changes in
carbon, nitrogen source
and
redox balance
.
Trehalose synthesis is mediated by
trehalose-6-phosphate
synthase
(T6PS) encoded by the
TPS1 gene
.
TPS1 controls expression of the
negative regulators
of
NCR
, which have been designated
NMR1,
NMR2
, and
NMR3
.
Trehalose-6-phosphate synthase (
Tps1
) integrates
glucose-6-phosphate
metabolism and
nitrogen source utilisation
by regulate
oxidative pentose phosphate
pathway
Tps1
directly binds to
NADPH
and regulates
transcriptional co-repressors
which comprise
Nmr1, Nmr2
and
Nmr3
which bind to
NADP
Tps1-dependent Nmr co-repressors
appear to control v
irulence-associated genes
that regulated by
GATA factors
and
NUT1.
De-repressed
during
appressorium-mediated plant infection
GATA factors
, Asd4 is for
rice blast disease
. When together, rice blast disease by
M. oryzae
requires
regulatory mechanism
involving
NADPH sensor protein
.
Tps1
is
NADP-dependent transcriptional co-repressors
and the balance of
NADPH
and
NADP
acting as
signal transducer
Introduction
Rice blast disease
- disease caused by fungus (
Magnaporthe oryzae
), causing a
lesion
to form on leaves, stems, peduncles, panicles, seeds, and roots.
Magnaporthe oryzae
an ascomycete fungus
can reproduce both sexually and asexually
produce specialized infectious structures:
-->
appressorium
- infect aerial tissues
-->
hyphae
- infect root tissues.
Disease cycle
conidia attach to host surface --> spore germinate --> germ tube develop --> appressorium formed --> penetration peg emergence --> invasive growth in host plant.
Reactive oxygen species generation during
appressorium differentiation in
M. oryzae
M. oryzae
must overcome the p
lant defence responses
during infection
Plant responses
to
attack
is the production of
reactive
oxygen species
(ROS) surrounding
infection sites
ROS are
toxic molecules
that trigger
programmed cell death
in infected plant cells
toughen
the
plant cell walls
Colonisation of rice leaves by
M. oryzae
Severely reduced after deletion of
SSD1 gene
, a
regulator of cell wall biogenesi
SSD1
is essential for the i
nitial establishment
of infection by avoiding the induction of
basal plant
defence responses
A number of
other proteins
have been
implicated
as
cellular redox sensors
such as the
metallothioneins
.
MMT1
gene encodes a
22 amino acids
metallothionein in
M. oryzae
MMT1 mutants
are
non-pathogenic
and unable to
cause
penetration-mediated penetration
on the host surface.
metallothioneins.
MMT1
is powerful
antitoxidant
and probably
plays a rol
e during process
oxidative cross-linking within the fungal cell wall
On the exposure to ROS, the virulence of
DcatB mutant
is
reduced
.
It is possible that
CATB
is also involved in
fungal cell wall biogenesis
and
differentiation
during
appressorium formatio
n and
penetration hypha productio
n.
Appressorium formation
unicellular, dome-shaped structure;
generates turgor pressure
to invade plant tissue.
formation depend on
environmental cues
hydrophobicity
hardness of the contact surface
plant cutin monomers (waxy polymer, constituent of plant cuticle)
nutrient starvation
appressorium can be formed on artificial plastic surfaces
BUT
need to be concerned on the
physical cues
and it is
less efficient
compared to formation on rice leaves due to
absence of cutin monomers
(formation of infection structure is not stimulated )
nutrient depletion (especially
nitrogen sources
) affect gene expression, growth & development --> starvation stress at leaf surface lead to appressorium formation
Appressorium differentiation
within 6-10h
melanin
formed in cell wall -->
cause appressorium to become darkly pigmented
Melanin
- important to
generate turgor
How turgor is generated?
accumulation of compatible solutes (glycerol) within infection structure --> pressure build-up at leaf surface, create force that allow penetration of hyphae appressorium base to plant cuticle
Glycerol synthesis
1) mobilization of lipid bodies from 3-celled conidium to developing appressorium
2) rapid breakdown of lipid & glycogen (* storage product also contributed to improve hyphae penetration & fungal growth
Non-pathogenic mutants (extra info)
do not synthesis melanin properly
(albino, rosy and buff coloured)
lack of
critical multi-functional fatty acid b-oxidation protein
(e.g: Mfp1)
lack of
carnitine acetyl transferase
- for
transport of acetyl CoA
across mitochondrial and/or peroxisomal membrane
Cell cycle control of appressorium
differentiation in
M. oryzae
How the appressorium initiate?
How it starts the infection?
a. Tear-drop shaped with 3 cells conidium lands on the rice leaf surface
b. Germinations starts when spore tip mucilage and producing narrow germ tube
c. 1 daughter nuclei moves to swollen germ tube tip and undergo mitosis
Infection-associated autophagy
Cell survival mechanism triggered by nutrient starvation
Can occur from conidial germination until formation of appressorium
Impairs appressorium formation
Mutate Pmk1 MAP kinase
Remove ATG8, ATG1 or related 16 genes necessary for non-selective macroautophagy
Apply exogenous nutrients
Deletion of genes essential to mitophagy or pexophagy has no effect impairing the appressorium formation
Tor (target of rapamycin) kinase protein - central regulator for starvation associated autophagy
Conclusion
The formation of these
infection cells
require
external physical responses
which is rapidly responding to
extra-cellular stresses
.
Such as the
absence of nutrients
, and
recycling the cells
to
fuel appressorium-mediated plant infection
.
Cell cycle
checkpoints govern the
appressorium development progression
and the
infection-associated autophagy
is
crucial
for
biological role of cells
Investigating
the relationship between
the
signaling pathway
to regulate appressorium development, the
regulation of cell cycle control
and precise mechanisms** by which environmental stress
perceived and elicits a response
holistic approach
utilising the range of platform genomic technologies for use in M. oryzae
to
determine
how
autophagy
is
initiated
and how it is
linked
to
appressorium morphogenesis
Carbon and nitrogen starvation in
M. oryzae
infection
Appressorium developed in absence of exogenous nutrients
Genes expressed during appressorium development
MPG1
hydrophobin
Hex1 Woronin
body associated gene
MSP1 gene
Genes that regulate N source utilisation in
M. oryzae
domain GATA-factor encoding gene
NUT1
