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Trichoderma–Plant–Pathogen Interactions: Advances in Genetics of…
Trichoderma–Plant–Pathogen Interactions: Advances in Genetics
of Biological Control
Interactions with Plant Pathogens
Bio-nematicides : can kill nematodes
Mycoparasitic interaction:
Sensing of the host/prey fungus
Attraction
Attachment,
Coiling around and
Lysis by hydrolytic enzymes and secondary metabolites
DOI 10.1007/s12088-012-0308-5
Mechanisms of
cell signaling
Seven transmembrane G protein coupled receptor Gpr1 is involved in sensing the fungal prey
Silencing of the gpr1 gene in
T. atroviride
caused the mycoparasite unable to respond to the presence host fungus
Ligand binds to receptor leads to downstream signaling events via activation of G-protein cascades
Deletion of the Tga3 Ga protein-encoding gene affected the mycoparasitic abilities of
T. atroviride
in a similar way to loss of Gpr1
Deletion of the adenylate cyclase gene
tac1
severely impaired growth and mycoparasitic abilities of
T. virens
Have 3 MAPK cascades:
MAPKKK, MAPKK and
MAPK
MAPK pathways may act in mycoparasitism and biocontrol
functions of signaling cascades in mycoparasitism and
related biocontrol properties
Attachment to Host fungi
Trichoderma
hydrophobins
used in mycoparasitism
proved in the existence of
T.virens
mutants in transcriptional regulator of secondary metabolites & in morphogenesis of Vel 1 where the hyrophobin expression has decreased.
Lack of hydrophobin shows that there’s a defect in hydrophobicity and mycoparasitism
attach and attack host through
appressoria/papillae like structure
coil around the host
releases antibiotics and hydrolytic enzymes.
glucanases
Deletion of tvbgn3 (b-1,6-glucanase-encoding) reduced the mycoparasitic and biocontrol potential of
T. virens
against
P. ultimum.
when over expressed of 2 b-glucanase(bgn2 & bgn3) improved biocontrol of T. virens against R. solani,
P. ultimum and Rhizopus oryzae
Protease
Prb1 & sp1 induced during mycoparasitism
chitinase
When deleted chit42/ech42, the use chitinase as a biocontrol is not severe.
secondary metabolites
Enriched in secondary metanolites coding genes
Roles of antimicrobial secondary metabolites such as gliotoxin and gliovirin in suppression of
R.solani
and
P.ultimum
have been suggested
The non-ribosomal peptide synthetase
Tex1 assembles an 18-residue peptaibol (trichovirin II)
using
Dtex1
mutants the trichovirin II type peptaibols
were shown to trigger induced resistance in plants
Rich in gene encoding enzymes
Trichoderma
Plant Interactions
Grow in Rhizosphere
( microecological zone in direct proximity of plant roots, operationally defined as; soil that clings to roots after being gently shaken in water. )
Source,
MicrobeWiki
Opportunistic/Facultative Symbiosis
Trichoderma
derives sucrose or other plant nutrients from plants
In return,
Trichoderma
help to;
Boosts plant immunity against invading pathogens
Improves photosynthetic abilities
Presence in rhizospehere evokes a coordinated transcriptomic, proteomic & metabolomic response in plant
Improves growth, yield and resistance to pathogens
2) Induced defense
Plants respond immediately to Trichoderma invasion by:
• rapid ion fluxes and an oxidative burst
• deposition of callose
• synthesis of polyphenols
Subsequent events involve salicylate (SA) and jasmonate/ethylene (JA/ET)-signaling, results in the entire plant acquiring varying degrees of tolerance to pathogen invasion
Described as JA/ET-mediated induced systemic resistance (ISR) and resembles the response triggered by plant growth-promoting rhizobacteria (PGPR).
Trichoderma can trigger a SA mediated systemic acquired resistance (SAR) response at higher inoculum
Implication of a mitogen-activated protein kinase (MAPK) from cucumber and a MAPK from
T. virens
in the molecular cross talk between plant and
Trichoderma
trigger the downstream defense responses
Xylanase and peptaibols produced by
Trichoderma
spp. were shown to elicit an immune response in plants
Sm1/Epl1, elicitor produced by
Trichoderma
spp. is abundantly secreted, small cysteine-rich hydrophobin-like protein of the cerato-platanin (CP) family
Monomeric form of Sm1 is in a glycosylated
Monomeric form in the non-glycosylated state is susceptible to oxidative-driven dimerization in plants rendering Sm1 inactive as inducer of ISR
1)
Root Colonization
Colonize plant roots internally and externally
Attraction of
Trichoderma
to plant roots is from interplay of chemical signals from both partners
Trichoderma
spp. produce and modulate hormonal signals in order to facilitate colonization of roots
Trichoderma produces auxins, that promote root growth
which in turns;
facilitates colonization by increasing available surface area
accd
(encodes ACC deaminase)
Trichoderma
deploys small secreted cysteine-rich hydrophobin-like proteins to facilitate attachment
Demonstrated by gene knockout ; e.g regulation of canola root growth by
T.asperellum
Trichodema spp. secretes expansin-like proteins with cellulose binding molecules & endopolygalacturonase ( to facilitate root penetration )
Root Invasion
Insides roots, fungi can grow inter-cellularly
(but limited to epidermal layer & outer cortex)
Initial supression of plant defense may facilitate root invasion
Example;
T.koningii
supresses production of phytoalexins during colonization of
Lotus japonicus
roots
3) The Endophytic Trichoderma
Some Trichoderma spp. are not restricted to outer root tissues, but can also live in the plant as ‘‘true’’ endophytes
The endophytic Trichoderma species are reported induce transcriptomic changes in plants and some protect plants from diseases and abiotic stresses
Some of endophytes preferentially colonize the surface of glandular trichomes and form appressoria-like structures (example of ‘‘non-root’’ mode of entry into the plant)
Introduction
Trichoderma spp. (teleomorph Hypocrea) are the most
successful biofungicides used
The major limitations of microbe-based fungicides are their restricted efficacy and their inconsistency under field condition
The origin is difficult as slow to react compared to chemical, influenced by environmental factors
‘‘genetic intervention" to design strains more effective than native
There's a plenty genetics of interactions of Trichoderma
with plants and pathogens
Lessons from Genome Sequencing
Mycoparasitic
Trichoderma
species frequently live in association with plant roots and living or dead fungal biomass
T. reesei
• found on decaying wood and, can secrete large amounts of cellulases and hemicellulases
• has the smallest genome (34.1 Mb, 9,129 gene models) probably resulting from a loss of mycoparasitism specific genes
T. atroviride
and
T. asperellum
• are phylogenetically ancestral species
• both are powerful antagonists of other fungi (necrotrophic mycoparasites).
T. virens
and
T. harzianum
• aggressive parasites of phytopathogenic fungi
• particularly effective in the stimulation of plant defense responses
Genes specific for mycoparasitism such as chitinases and some glucanases and those involved in secondary metabolite biosynthesis.
Trichoderma may have one of the largest sets of proteases among fungi.
Subtilisin-like proteases of the S8 family, dipeptidyl and tripeptidyl peptidases are expanded in the
mycoparasites
Conclusion
Depth understanding of the mechanisms is still
lacking
Also due to the lack of whole genome
sequences.
Some progress has already been made in this direction with
genome-wide expression studies
An international initiative should be undertaken to elucidate the unctions of each gene by high throughput gene knockouts
Optimal biocontrol and other biotechnological applications can be achieve if
Transcriptome analyses
under conditions of mycoparasitism and plant root colonization
Identifying novel candidate genes involved in the interactions of Trichoderma spp. with plants and plant pathogens.
