Trichoderma–Plant–Pathogen Interactions: Advances in Genetics
of Biological Control
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Introduction
Interactions with plant pathogens
Trichoderma spp. (teleomorph Hypocrea) are the most
successful biofungicides towards plants and pathogens
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origin of these difficulties
microbes are slow to act, compared to chemicals
Influenced by environmental factors
genetic
intervention
to design strains that are more effective than
the native ones might prove useful
To study the molecular mechanism of interaction of Trichoderma with other biotic and abiotic factors.
Example: Studies on the molecular genetic and physiology
Trichoderma–Plant Interactions
grow in the rhizosphere and are
capable of penetrating and internally colonizing plant roots
opportunistic/facultative symbiosis
derive sucrose or other nutrients
boost plant immunity
against invading pathogens
improve photosynthetic
abilities
The presence of Trichoderma in the rhizosphere evokes a coordinated transcriptomic, proteomic and
metabolomic response in the plant
Root Colonization
Mycoparasitism (Ability to parasitize and kill other fungi)
primary step
Attachment, penetration and internal colonization of plant
roots.
produce and modulate hormonal
signals in order to facilitate the colonization of roots.
Sensing of host/prey fungus (mycohost)
produces auxins that promote root growth
Attraction
facilitates colonization by increasing the available
surface area
Attachment
accd, encoding ACC deaminase, in regulation of canola root growth by T. asperellum
Killing the host by hydrolytic enzymes conjunction w secondary metabolite
Trichoderma deploys small secreted cysteine-rich hydrophobin-like proteins to facilitate anchoring/attachment.
Enzymes
Proteins that involved in attachment of root
Qid74 of T. harzianum
TasHyd1 from T. asperellum
Formation of appressoria/papillae likes structures
Trichoderma spp. secretes expansin-like
proteins with cellulose binding modules and endopolygalacturonase to facilitate root penetration
Induced Defense
rapid ion fluxes and an oxidative burst, followed by deposition of callose and synthesis of polyphenols
Coil around host hyphae
Subsequents event involve salicylate (SA) and jasmonate/
ethylene (JA/ET)-signaling
Might involves hydrophobins
results in the entire plant
acquiring varying degrees of tolerance to pathogen invasion
T. virens muntants in Vel1 - decreased hydrophobin expression
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JA/ET-mediated induced systemic resistance (ISR) and resembles the response triggered by plant growth-promoting rhizobacteria (PGPR)
Defective hydrophobicity and mycoparasitism
higher inoculum doses Trichoderma can trigger a SA-mediated systemic acquired resistance (SAR) response
Xylanase and peptaibols (peptaibiotics with high content of alpha amino isobutyric acid)
Chitinases
Glucanases
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Secondary metabolism
produced by Trichoderma spp.
elicit an immune response in plants
PKS/NRPS hybrid enzyme involved in defense
s Sm1/Epl1, an bundantly secreted, small cysteine-rich hydrophobin-like protein of the cerato-platanin (CP) family
Deletion gene impairs elicitation of ISR
The monomeric form of Sm1 is in a glycosylated state which is essential for elicitation properties.
monomeric form in the non-glycosylated state
susceptible to oxidative-driven dimerization in plants rendering Sm1 inactive as inducer of ISR
The Endophytic Trichoderma
Trichoderma spp. are not
restricted to outer root tissues,
Group of cell wall-lytic enzymes
also live in the plant
as ‘‘true’’ endophytes
Deletion of tvbgn3 (b-1,6-glucanase-
encoding)
Reduced the mycoparasitic and biocontrol
potential of T. virens against P. ultimum
Genome Sequencing
Co-overexpression
of two b-glucanases (Bgn2 and Bgn3)
T. reesei
Improved biocontrol of T. virens againts R. solani, P. ultimum, R. ortzae
Saprophyte
T. atroviride and T. asperellum are phylogenetically
secrete large amounts
of cellulases and hemicellulases
Decay Wood
powerful antagonists of other fungi (necrotrophic mycoparasites)
T. virens and T. harzianum
effective in the stimulation of plant
defense responses
Trichoderma may have one of the largest sets of proteases
among fungi.
Trichodema secretes cell wall-degrading (CWDEs)
Release degradation products from the host's cell wall
Act as signal recognition in the mycoparasite
seven transmembrane G proteincoupled receptor Gpr1 is involved in sensing fungal prey
Silencing of gpr1 gene in T. atroviride make the mycoparasite unable to respond to presence of host fungus
Effect of deletion of chit42lech42 were nit drastic
Gliotoxin and gliovirin
In suppressing R. solani and P. ultimum have been suggested
Tex1 assembles ab 18-resude peptaibol (trichovirin 2)
Trigger induced resistance in plants
T. atroviride produce volatile metabolite
6-pentyl-2H-pyran-2-one (6-PP)
Important in Trichoderma-plant and Trichoderma-fungal interaction