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Trichoderma-Plant-Pathogen Interactions: Advances in Genetics of…
Trichoderma
-Plant-Pathogen Interactions: Advances in Genetics of Biological control
Killing the host
: Production of hydrolytic and enzymes and antibiotics
Hydrolytic enzymes and antibiotics are important in
Trichodema
to kill other fungi
genomes of mycoparasitic
Trichoderma spp
. rich in genes encoding enzymes (chitinases and glucanases) and for secondary metabolism (NRPSs)
chitinases though the effect of deletion of
chit42/ech42
glucanases- group of cell wall-lytic enzymes with roles in mycoparasitism/biocontrol
deletion of
tvbgn3
-reduce the mycoparasitic and biocontrol potential of
T.virens
against
P.ultimum
Trichoderma spp
.are prolific producers of secondary metabolites and genomes of mycoparasitic
the non-ribosomal peptide synthetase Tex 1 -trigger induced resistance in plants
Attachment to host fungi
by formation of appressoria- or papillae-like structures and coiling around host hyphae
involvement of hydrophobins from finding
T.virens
mutans
hydrophobins- able to form a hydrophobic coating on the surface of an object
T.virens
have low hydrophobin expression will damaged in both hydrophobicity and mycoparaisitism
Induced Defense
Plant-->
Trichoderma
invade
ion fluxes + oxidative burst
deposition of callose synthesis of polyphenols
Next, salicylate (SA)+ jasmonate/ethylene (JA/ET)-signaling
Result: plant will have diff degrees of tolerance to the pathogen invasion
This response describe as JA/ET-mediated induce systemic resistance(ISR)-->resemble the response--> triggered by--> plant growth-promoting rhizobacteria (PGPR)
At higher doses of
Trichoderma
its trigger a SA-mediated systemic acquired resistance (SAR) response(similar to necrotrophic pathogens)
From implication of
1) mitogen-activated protein kinase (MAPK) from cucumber,and
2) MAPK from
T. virens
in the molecular cross between plant and
Trichoderma
Result: triggering the downstream defense responses
Immune response in plants elicit:
When,
Trichoderma
produces:
1)Xylanase
2)peptaibols (peptaibiotics with high content
of alpha amino isobutyric acid) like alamethicin and trichovirin II
PKS/NRPS hybrid enzyme involved in defense
responses in maize
Sm1/Epl1=eliciitor produced by
Trichoderma
:
Deletion of this
Trichoderma
gene impairs elicitation of ISR in maize
Monomeric form of Sm1(in a glycosylated state)=essential for elicitation properties.
Non-glycosylated state=susceptible to oxidative-driven dimerization in plants rendering Sm1 inactive as inducer of ISR
The Endophytic
Trichoderma
Some
Trichoderma spp
. are:
1)Not restricted to outer root tissues
2)Can also live in the plant as ‘‘true’’ endophytes
Endophytic
Trichoderma
species:
1)Induce transcriptomic changes in plants
2)Protect plants from diseases and abiotic stresses
3)preferentially colonize the surface of glandular trichomes and form appressoria-like structure
4)Uses a ‘‘non-root’’ mode of entry into the plant.
Conclusion
international initiative should be taken to state the functions of each gene by high throughput gene knockouts as accomplished with
N.crassa
in anexemplary community effort
transcriptome analyses under conditions of mycoparasitism and plant root colonization will help in identifying novel candidate genes
Interaction with plant pathogen
Mycoparasitism is a trait present in all
Trichoderma
sp. -> can parasitize and kill other fungi.
Some fungus can kill nematodes (bio-nematicides).
Mycoparasitism steps: sensing of host/prey fungus -> attraction -> attachment -> coiling around -> lysis by hydrolytic enzymes work together with other secondary metabolites.
Environmental signaling
: Importance of signaling cascades in mycoparasitism.
Seven transmembrane G-protein coupled receptor
Gpr1
sense fungal prey because mutation (silencing)
grp1
gene cause mycoparasite unable to respond to fungus.
Ligand bind to these receptors activate
G-protein cascades
.
Deletion of
Tga3
G-alpha protein-encoding gene also cause loss of response (sensing).
Deletion of adenylate cyclase gene
tac1
severely affected
T. virens
growth and mycoparasitic abilities.
MAPK pathway with 3 cascades (MAPK, MAPKK and MAPKKK) important in mycoparasitism and control.
1) Trichoderma sp. secretes cell wall degrading enzymes to break down cell wall -> obtain product (signals to recognise host - to know where and whether it is the host plant).
"
Kinase
adds phosphate groups (phosphorylation)"
2) Binding of ligand to receptors activate G-protein signaling/ cascades -> downstream MAPK (phosphorylation each step) and cAMP pathway.
3) MAPK activates "cellular processes" by regulation (act as downstream effectors) and further induce (full induction) secretes more cell-wall degrading enzymes and secondary metabolism.
Plant Interaction
grows in rhizosphere - capable penetrate int and ext of plant root
Opportunist
/
Facultative
symbiosis
Trichoderma Benefits
: Abilty
derive
sucrose
/ other nutrients from plants
Plants Benefits
: Boost
immunity
against invading pathogen,
Improve
photosynthetic abilities.
Root interaction
: produces
auxin
in promote root growth and gain colonization by the increases of surface area
Root Penetration: Expansion- like protein and cellulose binding modules & endopolygalucturonase
Introduction
used as biofungicide - induction plant defense and mycoparasitism
limitations:
restricted efficacy & inconsistency due to env factor
Overcome
: Genetic Intervention
Lessons from Genome Sequencing
Only the genome of five
Trichoderma
sp. is available.
T. atroviride
and
T. esperellum
(ancestral sp.) kill other fungus effectively (necrotrophic: killing host cells and break-down decaying tissues.
T. virens
and
T. harzianum
kill phytopathigenic fungi -> stimulate plant defense mechanism.
T. reesei
(a saprophytic fungus found in decaying wood) has the smallest genome maybe due to loss of certain mycoparasitic genes.
Mycoparasites live with plant roots and living or dead fungal biomass.
Gene expansion (increase in nucleotides) due to the fungus adaptation to its antagonistic nature.
Genes specific for mycoparasitism (chitinase & glucanase) & for secondary metabolite biosynthesis
Trichoderma sp. has among the largest set of proteases such as subtilisin-like proteases, dipeptidyl and tripeptidyl peptidases.
Mycoparasitic genes are expressed during or before contact with host/prey.