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