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Trichoderma–Plant–Pathogen Interactions: Advances in Genetics of…
Trichoderma–
Plant–Pathogen Interactions:
Advances in Genetics
of Biological Control
Introduction
Trichoderma
spp.
(teleomorph
Hypocrea
)
:pencil2: most successful biofungicides used in today’s agriculture
:pencil2: The major limitations of microbe-based fungicides are their restricted efficacy and their inconsistency under field conditions.
:pencil2: The origin of these difficulties is that microbes are slow to act, compared to chemicals, and are influenced by environmental factors.
:pencil2: ‘‘genetic intervention’’ = to design strains that are more effective than the native ones might prove useful.
Induced Defense
plants respond to
Trichoderma
invasion by:
rapid ion fluxes
an oxidative burst
followed by;
deposition of callose
synthesis of polyphenols
involve salicylate (SA) & jasmonate/ethylene (JA/ET) signaling
plant acquired vary degrees to tolerance to pathogen invasion
JA/ET-mediated Induced Systemic Resistance (ISR)
resembles the response triggered by plant growth-promoting rhizobacteria (PGPR)
Tricoderma
trigger a SA-mediated systemic acquired resistance response
deletion
Trichoderma
gene impairs elicitation of ISR in maize
best characterized elicitor
Sm1/Ep11
(abundantly secreted, small cysteine-rich hydrophobin-like protein of cerato-platanin (CP) family
monomeric form; non-glycosylated state:-
susceptible to oxidative-driven dimerization in plants rendering Sm1 inactive (inducer of ISR)
mitogen - activated protein kinase
(MAPK) from cucumber and MAPK from T. virens:
triggering the downstream defense response
implications:
xylanase and peptainot :
elicit an immune response in plants
Interactions with Plant Pathogens
Attachment to Host Fungi
Appressoria formed upon attachment to and attack of host fungi by mycoparasitic
Trichoderma
Genetics underlying attachment of mycoparasite to host fungus are not well understood
Hydrophobins possibly involved
~
T. virens
mutants in transcriptional regulator of secondary metabolism and morphogenesis Vel 1
~ morphogenesis Vel 1 decrease hydrophobin expression
Mycoparasitism
~ Ancestral trait of
Trichoderma/Hypocrea
Typical mycoparasitic interaction brought about by hydrolytic enzymes involves
~ Sensing of host/prey fungus
~ Attraction
~ Attachment
~ Coiling around
~ Lysis
Environmental signaling
Image link
Trichoderma
– Plant Interactions
many
Trichoderma
species:
:black_circle: grow in the rhizosphere
:black_circle: are capable of penetrating and internally colonizing plant roots (facultative symbiosis)
:black_circle: presence of
Trichoderma
in the rhizosphere evokes a coordinated transcriptomic, proteomic and metabolomic response in the plant
Conclusion
The availability of five Trichoderma genomes will allow us to understand the mechanisms in depth
Functions of each gene should be elucidated by high throughput gene knockouts
Identification of novel genes involved in the interaction between Trichoderma spp., plant and pathogen will allow us to engineer strains for optimal biocontrol and biotechnological applications
Root colonization
:arrow_forward: Trichoderma spp. can colonize plant roots, both externally and internally
:arrow_forward: Attachment, penetration and internal colonization of plant roots.
:arrow_forward:
TasHyd1 from
T. asperellum
and
Qid74 of
T. harzianum
= the proteins have been found to facilitate attachment to the roots
:arrow_forward:
Trichoderma
spp. produce and modulate hormonal signals to facilitate the colonization of roots.
:arrow_forward: Trichoderma deploys small secreted cysteine-rich hydrophobin-like proteins to facilitate anchoring/attachment.
:arrow_forward: The fungus produces auxins that promote root growth which facilitates colonization by increasing the available surface area.
:arrow_forward:
Trichoderma
spp. secretes expansin-like proteins with cellulose binding modules and endopolygalacturonase to facilitate root penetration
:arrow_forward: These fungi can grow inter-cellularly, albeit limited to epidermal layer and outer cortex once inside the roots.
:arrow_forward: Initial suppression of plant defense may facilitate root invasion.
Killing the host: Production of Hydrolytic Enzyme & Antibiotics
Trichoderma spp. are rich in gene that encode for
Enzymes
chitinase
glucanase
protease
Deletion of genes encoding these enzymes reduce the mycoparasitic and biocontrol potential
Co--over expression of these genes improve the biocontrol and mycoparasitic potential
Secondary metabolites
NRPSs
gliotoxin
gliovirin
Lessons from Genome Sequencing
shows the importance of the genes in attacking and killing the fungal prey
supports the adaptation of this mycoparasitic fungi (Trichoderma sp) to their antagonistic lifestyle
There are genome sequence of 5 species
T. reesei (34.1 Mb)
T. atroviride (36.1 Mb)
T. virens (38.8 Mb )
T. harzianum (40.98 Mb)
T. asperellum (37.4 Mb)
Found at:
decaying wood
soil
living or dead fungal biomass
associated with plant roots
T. virens and T. harzianum are aggressive parasites of phytopathogenic fungi and are particularly effective in the stimulation of plant defense responses
T. atroviride and T. asperellum are phylogenetically ancestral species and both are powerful antagonists of other fungi (necrotrophic mycoparasites).
Involves expansion of several gene families; such as chitinase, some glucanases and genes involved in secondary metabolite biosynthesis
Many of these genes are expressed before and during contact with the host/prey fungus
Secretome analysis revealed that Trichoderma may have one of the largest sets of proteases among fungi
Subtilisin-like proteases of S8 family
dipeptidyl & tripeptidyl peptidase
The endophytic
Trichoderma
Trichoderma
spp.
some are not restricted to outer root tissue
can also live in plants as "true" endophytes
"new" species of endophytic
Trichoderma
:
T. stromaticom, T. amazonicum, T. evansii, T. martiale, T. taxi
and
T. theobromicola
induced transcriptomic changes in plants
to protect plants from disease & abiotic stresses
colonize the surface of glandular trichomes & form appressoria - like structure (uses a "non-root" mode of entry into the plant
