Trichoderma-Plant-Pathogen Interactions: Advances in Genetics of Biological control

Killing the host: Production of hydrolytic and enzymes and antibiotics

Attachment to host fungi

Induced Defense

The Endophytic Trichoderma

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)

by formation of appressoria- or papillae-like structures and coiling around host hyphae

At higher doses of Trichoderma


its trigger a SA-mediated systemic acquired resistance (SAR) response(similar to necrotrophic pathogens)

involvement of hydrophobins from finding T.virens mutans

T.virens have low hydrophobin expression will damaged in both hydrophobicity and mycoparaisitism

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)

hydrophobins- able to form a hydrophobic coating on the surface of an object

Conclusion

Interaction with plant pathogen

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

Mycoparasitism is a trait present in all Trichoderma sp. -> can parasitize and kill other fungi.

chitinases though the effect of deletion of chit42/ech42

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

glucanases- group of cell wall-lytic enzymes with roles in mycoparasitism/biocontrol

Plants Benefits: Boost immunity against invading pathogen, Improve photosynthetic abilities.

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

deletion of tvbgn3-reduce the mycoparasitic and biocontrol potential of T.virens against P.ultimum

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.

Trichoderma spp.are prolific producers of secondary metabolites and genomes of mycoparasitic

Root interaction: produces auxin in promote root growth and gain colonization by the increases of surface area

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

Root Penetration: Expansion- like protein and cellulose binding modules & endopolygalucturonase

Environmental signaling: Importance of signaling cascades in mycoparasitism.

Introduction

Seven transmembrane G-protein coupled receptor Gpr1 sense fungal prey because mutation (silencing) grp1 gene cause mycoparasite unable to respond to fungus.

used as biofungicide - induction plant defense and mycoparasitism

the non-ribosomal peptide synthetase Tex 1 -trigger induced resistance in plants

limitations: restricted efficacy & inconsistency due to env factor

Overcome: Genetic Intervention

Ligand bind to these receptors activate G-protein cascades.

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

Deletion of Tga3 G-alpha protein-encoding gene also cause loss of response (sensing).

transcriptome analyses under conditions of mycoparasitism and plant root colonization will help in identifying novel candidate genes

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.

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.

Lessons from Genome Sequencing

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.

Only the genome of five Trichoderma sp. is available.

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.

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.

Gene expansion (increase in nucleotides) due to the fungus adaptation to its antagonistic nature.

Genes specific for mycoparasitism (chitinase & glucanase) & for secondary metabolite biosynthesis

Mycoparasitic genes are expressed during or before contact with host/prey.

Trichoderma sp. has among the largest set of proteases such as subtilisin-like proteases, dipeptidyl and tripeptidyl peptidases.