GH3 Project

• They discovered dn-OPDA-aa conjugates (Glu, His, Gln) and their accumulation upon wounding and exposure to herbivors.

• gh3A mutants did not accumulate these compounds.

• Instead, they accumulate the wound ligand, show a constitutive wound response and are resistant to the pathogens they tested.

• gh3A mutants were more susceptible to OPDA treatment (reduced growth)

• differences were also noticeable in gene expression (upregulation of wound-response genes even under mock conditions and more than in the wt under OPDA treatment)

—> Conjugation of the wound ligand with aas takes place to contain the wound response.

Processes:

• seed germination

• root growth and development

• stamen development

• leaf senescence

• photosynthesis

• reproduction

• …

There are several mechanisms by which the plant “decides” which response to jasmonates to initiate:

• presence or absence of response-specific receptors (e.g., in different tissues)

• cross-talk with other hormones (e.g., cross-inhibition between SA and JA responses to pathogens; JA is responsible for necrotrophic pathogens and herbivores, SA for biotrophic pathogens)

• signal modulation

• …

The JA-Ile-mediated wound response is activated against herbivors and necrotrophic pathogens.

• Protease Inhibitors, to inhibit digestive enzymes from herbivores.

• Secondary metabolite pathways (alcaloids, flavonoids, glucosinolates), to deter herbivors/pathogens (potentially toxic)

• Cell Wall Reinforcement (lignin, callose)

• Systemic Signaling Production (other jasmonates, systemin), to “inform” other parts of the plants of the attack

• ROS accumulation

• Regeneration of tissue

• one amino acid residue in COI1 altering the size of the binding pocket

• some amino acids in the degron of the JAZ

thermotolerance and response to other abiotic stresses in streptophytes

flavonoids = polyphenols

• accumule in and thus strenghen the cell wall

• antimicrobial effect (quercetin, catechin discrupt cell membranes)

• ROS neutralization

• UV protection

• systemic transmission of defense signals

Synthesis via the phenylpropanoid pathway (phenylalanine - PAL - cinnamic acid - coumaric acid, coumaroyl-CoA) and the polyketide pathway (coumaroyl-CoA + 3 malonyl-CoA —> chalcone) with subsequent further modifications

• flavonoids

• lignin

• coumarin

• salicylic acid

• suberin and cutin

• …

benzyl ring with usually C3 side chain

• MS/MS spectra to check if the fragmentation makes sense

• artifical synthesis of the suspected compound and comparison of

  • fragmentation pattern

  • isotope pattern

  • chemical derivatization (improved detection, stability, separation, but mostly extra information about structure due to characteristic fragmentation)

    • example: DMOX derivatization of fatty acids allows the localization of double bonds

  • retention times

• If sufficient amounts (pure) are available: NMR, IR

jasmonate

jasmonate-Ile

jasmonate-Me

auxin/IAA

gibberellins

cytokinines

ethylen

abscisic acid

strigolactones

brassinosteroids

salicylic acid

auxins: substances with auxin effect, e.g. IAA, IBA, “Agent Orange” (herbicide, strong auxin, results in premature senescence, used in Vietnam war to defoliate the forest)

Processes:

• embryogenesis

• organogenesis

  • leaf development

  • secondary root development

  • vascular tissue development

  • fruit development

• root growth

• apical dominance

• phototropism

• gravitropism

Many of the functions take place due to asymmetrical distribution of auxins in the cell or the plant.

There are three known biosynthesis pathways for IAA, all starting from tryptophane.

Receptors:

• ABP1 (auxin-binding protein 1): fast reaction, binds to receptor outside the plasma membrane

  • loosening of the cell wall, elongation of the cell after 10 min

• TIR1/AUX-IAA-TFs (transport-insensitive response 1/): similar mechanism as COI1/JAZ, ARF ^= MYC2

• SKP2A

  • activation of cell division

• jasmonates

• systemin

• ROS

• volatile compounds (e.g., terpenes)

• detection of mechanical damage

  • wall-associated kinases (WAKs) detect cell wall damage and trigger signaling cascades

  • influx of Ca2+ ions through damaged plasma membranes

    • activation of Ca2+-binding proteins (calmodulin)

• as a result, DAMPs (damage-associated molecular patterns) are released from the ruptured cell

  • pectin fragments, ATP, proteins like systemin

  • result in a wound response in neighboring cells

Generally: Introduction of the hydroperoxy group at either C13 or C9.

HPL (hydroperoxy lyase):

• cleavage of 13-HPOT and other hydroperoxy fatty acids

• products: grean leaf volatiles (C6 alcohols and aldehydes

• functions:

  • attract pathogen enemies (e.g. some wasp species)

  • warn neighboring plants

  • antimicrobial properties

DES (divinyl ether synthase)

• convertes 13-HPOT into divinyl ethers

• functions

  • antimicrobial properties

  • (localized plant response)

Histone deacetylases deacetylate histones, leading to an increased positive charge, which results in increased interaction with the negatively charged DNA —> silencing

During the wound response, they are recruited by TOPLESS, which binds to NINJA which binds to JAZ proteins which bind to MYC2

• Nonvascular plants have OPDA and dnOPDA but no JA-Ile.

• JA is present in all vascular plants and some nonvascular plants.

  • OPR3-independent JA synthesis emerged in charophtes (degradation pathway?)

  • OPR3-dependent JA synthesis emerged in vascular plants

• JA-Ile first appears in the lycophyte Selaginella moellendorfii, but not as a ligand for COI1/JAZ (degradation?)

• Plants with high (dn-)OPDA levels usually have no or low JA levels and vice versa

• in nonvascular plants, dn-OPDAs are most likely the wound ligands

family of proteins that activate carboxylate substrates

A: Acyl-CoA synthetases

N: Non-ribosomal peptide synthetase adenylation domains

L: Luciferase

Mechanism:

• acyl-substrate is AMP-ylated, releasing PPi

• nucleophile attack, releasing the product and AMP

They appear to be involved in auxin homeostasis by conjugating IAA to amino acids - inactivation/degradation?

In M. polymorpha, a similar mechanism has been found for dn-OPDA, presumably attenuating the wound response.