Presentation on theme: "Plant Defense and Secondary metabolism"— Presentation transcript:
1 Plant Defense and Secondary metabolism General introduction to plant defense and attraction
2 Multitrophic Interactions Plant Defense:Multitrophic InteractionsSecondary carnivoresCarnivoresHerbivoresPollinatorsShoots and flowersCompetitor plantsPathogensAbovegroundBelowgroundRootsPathogensParasitic plantsHerbivoresSymbiontsCarnivoresModified from Bruinsima & Dicke 2008
3 Plants respond to attacks by herbivores and pathogens Plants use defense systems to deter herbivory, prevent infection, and combat pathogensHerbivory, animals eating plants, is a stress that plantsPlants counter excessive herbivory with physical defenses such as thorns and chemical defenses such as distasteful or toxic compoundsSome plants even “recruit” predatory animals that help defend against specific herbivores
4 Plant Response to Herbivores Plant Defense Traits
5 Plant Response to Herbivores Plants damaged by insects can release volatile chemicals to warn other plants of the same speciesThese volatile molecules can also function as an “early warning system” for nearby plants of the same species.Methyljasmonic acid can activate the expression of genes involved in plant defenses
6 Jasmonic Acid Levels of jasmonic acid rise in response to damage This hormone can trigger many types of plant defenses including terpenes and alkaloidsThe action of jasmonic acid induces the transcription of many genes involved in plant defenseJasmonic acid turns on genes for proteinase inhibitor.
8 Plant defense traitsPlants use a variety of mechanical (toughness, spines), chemical (alkaloids, phenolics, terpenoids, latex – the realm of chemical ecology), developmental, and phenological defensesDefenses may also be classified with reference to their production:1. Constitutive – produced by & present in the plant irrespective of attack2. Induced – produced by & present in the plant in response to attack
9 Plant defense traits Resistance traits Those traits that “reduce herbivory”Avoidance (antixenosis) traitsThose traits that “affect herbivore behavior;” i.e., deter or repel herbivoresb. Antibiosis traitsThose that “reduce herbivore performance”2. Tolerance traitsThose traits that “reduce the impact of herbivory on fitness”
10 Resistant vs Tolerant Resistant Tolerant Susceptible For illustration, I have a resistant, tolerant, and susceptible (or non-defended) plant represented in this cartoon. In the presence of herbivores…Resistant Tolerant Susceptible
11 Benefits of defense are obvious in the presence of herbivores Resistant vs TolerantBenefits of defense are obvious in the presence of herbivoresThe benefit of investing in defense is increased fitness in the presence of herbivores relative to susceptible genotypes.Resistant Tolerant Susceptible
12 Costs of defense are obvious in the absence of herbivores Resistant vs TolerantCosts of defense are obvious in the absence of herbivoresHowever, the production and maintenance of defense traits and mechanisms may incur a cost to the plant when herbivores are rare or absent. So resistant and tolerant plants would be expected to have lower fitness than non-defended plants when herbivores are absent.Resistant Tolerant SusceptibleSlide courtesy of Alyssa Stocks Hakes; modified from the original
13 Resistance Traits DIRECT INDIRECT Slide courtesy of Amanda Accamando; modified from the original
15 Direct Defense Morphological Characters Secondary metabolites E.g., Tannins
16 Cutin, Waxes, SuberinsAll plant parts exposed to the atmosphere are coated with layers of lipid material that reduce water loss and help block the entry of pathogen fungi and bacteriaThe principal types of coating are cutin, suberin and waxesThey are made of hydrophobic compounds which have water-repelling propertiesThese compounds are non-polarFatty acids are one type of hydrophobic compound
17 Cutin It is found most above ground It is a macromolecule, a polymer composed of long fatty acid chains that are attached to each other by ester linkage, creating a rigid three dimensional networkIt was a major component of plant cuticle, a multilayered secreted structure that coats the outer cell wall of epidermis on the areal partsPlants’ cuticles is composed of a top coating of wax, often vary with the climate in which they live.
19 WaxesComplex mixtures of long-chain lipids that are extremely hydrophobic.The most common components of waxes are straight chain alkanes and alcohol of 25 to 35 carbon atoms.They are synthesized by epidermal cells.They exuded through pores in the epidermal cell wall by an unknown mechanism.
20 SuberinIt was formed from fatty acids but has a different structure from cutin.It was often within roots.It can protect against pathogens and other damage.It can form transport barriers between the soil and the rootsOlder parts of roots more suberizedA cell wall constituentEndodermis has suberin side walls
22 End points of metabolism with no strictly defined function Secondary metabolitesEnd points of metabolism with no strictly defined functionOrganic compounds that appear to have no direct function in photosynthesis, growth, or respiration, but 1. They protect primary metabolism by deterring herbivores, reduce tissue loss and avoid infection by microbial pathogen 2. They also attract pollinators and seed-dispersing animals, 3. They act as an agent of plant-plant competition 4. They are formed from the byproducts or intermediates of primary metabolism
23 Three Principal Groups of Secondary Metabolites TerpenesLipid synthesized from acetyl CoA or from basic intermediates of glycolysisPhenolic compoundsAromatic substances formed via the shikimic acid pathway or the malonic acid pathwayNitrogen containing secondary products (alkaloids)Alkaloids which are synthesized primary from amino acids
24 Plant is more than primary metabolism: more than sugars and starch, and proteins etc, extracting compounds from the primary C pathways for biosynthetic purposes
25 Important part of plant metabolism is geared towards plant defense
26 Terpenes They produced from the mevalonic acid pathway They function as herbivore deterrentsThey can be produced in response to herbivore feeding, and to attract predatory insects and parasites of the feeding herbivore.They are constituents of essential oilsBuilding block- 5 C isoprene unitThey are classified by the number of isoprene units: monoterpenes-1, diterpenes-4
29 Isoprene H3C CH CH CH2 H2C The basic building block of the terpenes (terpenes also called “isoprenoids”)H3CCHCHCH2H2CTerpenes:Monoterpenes have two C5 units (10C)Sesquiterpenes have three C5 units (15C)Diterpenes have four C5 units (20C)Triterpenes 30 CTetraterpenes 40CPolyterpenes ([C5]n), n>8
30 Terpene functions Growth and development carotenoid pigments are tetraterpeneschlorophyll side chain is diterpenegiberellins (hormones) are diterpenesabscissic acid (hormone) is a sesquiterpene C15sterols are triterpenes
31 1. Resins of conifers are monoterpenes 2. Defensive compoundsToxins and feeding deterrents to insects and mammalsExamples1. Resins of conifers are monoterpenes2. Essential oils - peppermint, limon,
37 Terpenes that act against vertebrate herbivores Triterpenes1. Cardenolides (glycosides) - acutely toxicinfluence Na+/K+ ATPase of heart musclemedicinal application - digitalis (from foxglove), used totreat heart disease. Can slow and strengthen heart beat2. Saponins (soaplike) - steroid, triterpenes glycosideshave lipid and water soluble parts of moleculetoxicity related to sterol binding, membrane disruption
38 Terpenes as human medicinal drugs Limonene - monoterpenoid (C10) dietary anticarcinogenArtemisnin - sesquiterpenoid (C15) antimalarialTaxol - diterpenoid anticancer drug from Pacific yew (Taxus brevifolia)
39 PhenolicsPlants produce a variety of compounds that contain one or more phenol groups - called phenolicsThousands of phenolics occur in plants
40 Phenolic CompoundsSecondary metabolites which contain a hydroxyl functional group on an aromatic ringThey are heterogenous group:Some are water soluble only in organic solventsSome are water soluble carboxylic acids and glycosidesSome are insoluble polymerMany serves as defense compounds against herbivores and pathogensOther function in attracting pollinators and fruit dispensers
41 Types of Phenolic Compounds Benzoic acid derivativesCaffeic acid and other simple phenylpropanoidsFlavonesIsiplavones (Isoplavonoids)FlavonoidsLignin
42 N-containing secondary compounds Those are encountered less commonly in plants than the phenolics and terpenoidsThose are important in view of their bioactivity as drugs and toxinsThey are synthesized from aliphatic and aromatic amino acidsAliphatics via TCA cycleAromatics via shikimic acid pathway
43 Classes of N-containing 2o compounds Alkaloids,Cyanogenic glycosides,Glucosinolates,Nonprotein amino acids
44 1. ALKALOIDS The most important nitrogen containing secondary products They are being found in more than 15,000 compounds found in 20% of vascular plants.Nitrogen is usually part of a heterocyclic ring with N and C atoms
46 ALKALOIDS Large pharmacological effects on animals Most effective at deterring mammalian herbivoresLivestock deaths due to over-consumption of alkaloid containing plants such as lupines and groundselsOften alkaloids are used as medicines for humansSome examples: morphine, codeine, and scopolaminecocaine, nicotine, and caffeine used as stimulants and sedatives.
47 Wild tobacco (Nicotiana sylvestrus) Wild tobacco can “sense” which herbivore is feeding on it. It normally produces nicotine (an alkaloid) in response to herbivore feeding. But if nicotine-tolerant caterpillars are feeding, the tobacco produces terpenes instead. These terpenes can attract the predators of the herbivore.
48 2. CYANOGENIC GLYCOSIDES Release the toxic gas hydrogen cyanide.plants must have enzymes to break down the compounds and release a sugar molecule yielding a compound that can decompose to form HCN.glycosides and enzymes which break them down are usually spatially separated (in different cellular compartments or different tissues)
49 The degradation process is stimulated by herbivore feeding Cyanogenic GlycosidesThe degradation process is stimulated by herbivore feedingPP13200.jpg
50 Cyanogenic Glycosides S. American native peoples eat cassava (Manihot esculenta), has high levels of cyanogenic glycosides. Chronic cyanide poisoning are not uncommon.PP13200.jpg
51 3. GLUCOSINOLATESThese compounds release volatile defensive substances, “mustard oils”, (often herbivore repellents)Plants like cabbage, broccoli, and radishes (Brassicaceae family) have these.
52 4. NON-PROTEIN AMINO ACIDS These amino acids are not incorporated into proteins but instead act as protective substancescan “mistakenly” be incorporated into protein and therefore resulting in a nonfunctional protein.
54 Functions of Secondary Metabolites in Plants The secondary metabolites have no function in the physiology of the plantsThey are formed as a result of an overspill from the primary metabolismThey make a valuable contribution to the relationship between plant and their environmentPlant utilized secondary metabolites as antibiotics or signaling agent during the interaction with pathogen (SAR and Agrobacterium)They play an important role in two resistance strategies:a. structural level, phenyl propanoids are the majorcomponent of wall polymers lignin and suberinb. Inducible defence antibiotics originated from phenolics,and terpenoids (phytoalexins)
55 Herbivore damage can elicit a Signaling Pathway (Induced Defenses) Resistance Traits:Indirect DefenseInduced defenses:a. Recognition of the pathogen by the host plant; carbohydrates, fatty acids released by fungib. Transmission of alarm signal to host; Ca, hydrogen peroxide, enzymes.Herbivore damage can elicit a Signaling Pathway (Induced Defenses)
57 Induced biochemical defenses Hypersensitive reactions (phytoalexins, antimicrobials (important with obligates parasites – rusts, leaf spots, active oxygen radicals disrupt cell membranes, reinforcement of host cell walls)Antimicrobials – phytoalexins, phenolicsImmunizationLocal and systemic acquired resistance
58 (Phyto = “plant” and alexin = “to ward off/”) Phytoalexins(Phyto = “plant” and alexin = “to ward off/”)Low molecular mass antimicrobial metabolites synthesized de novo from primary metabolites in response to infectionStructurally diverse group of metabolites with the isoflavonoids can be an exampleThe isoflavonoids phytolaexins are synthesized from the flavonoids branch of the phenylpropanoid pathways
59 PRODUCTION OF PHYTOALEXINS Production of phytoalexins may be stimulated by certain compounds called elicitors.High molecular weight substances found in the cell wall such as glucans, glycoprotein, or other polysaccharidesGases such as ethylene (C2H4)In susceptible plants, a pathogen may prevent the formation of phytoalexins, by the action of suppressors produced by the pathogenThe suppressor also can be a glucan, a glycoprotein, or a toxin produced by the pathogen
60 How are Phytoalexins Formed? The “-noids”Shikimic acid pathway (phenylpropanoids)Hydroxycinnamic acidsCoumarinsHydroxybenzoic acidsMevalonic acid pathway (Isoprenoids)CarotenoidsTerpenoidsCombination of Pathways Shikimic-Polymalonic)Flavonoids and anthocyanins
61 Signaling Cascade for Defense Responses Molecular nature of elicitors:Cell wall proteins (e.g., Harpin)Intracellular proteins (defined genetically in a bacterium by cloning avirulent loci)Peptide derived from a larger protein (from a fungus)Heptaglucan (small oligosaccharide)
62 Secondary Signals Ca+2 , required for subsequent steps May mediate phosphorylation-dephos. events involved in transcriptional or post- transcriptional gene regulation (there are a number of genes whose transcription increases, and some decrease)Some defense genes also induced by blue-UV light or other stresses
64 Secondary Signals 3. Salicylic acid required for SAR levels increase locally and at distance from infectionSystemic Signal? Probably not. Still unknown
65 Signaling Cascade for Defense Responses Model derived mostly from studies in cell culture using specific elicitors.However, there is evidence for induction in intact plants by R genes. Some aspects are also constitutive and help block most microbes (non-host resistance).
67 Systemic Acquired Resistance Systemic acquired resistance causes systemic expression of defense genes and is a long-lasting responseSalicylic acid is synthesized around the infection site and is likely the signal that triggers systemic acquired resistanceWhen a plant survives the infection of a pathogen at one site it can develop increased resistance to subsequent attacks.Although plants don’t have “immune systems” they have signaling mechanisms that can act in this way.
69 Genetice model for SAR Infected Tissue Non-infected Tissue INA BTH Isd6Cpr1?Isd2Isd4nim1npr1Ndr1?Cpr1Cin2Cin3NahGLocalAcquiredResistancePlant PathogenInteractionSalicylicAcidSAR geneExpressionNecrosisINABTHNon-infected Tissuenim1npr1NahGSystemicAcquiredResistanceSalicylicAcidSAR geneExpression