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.