“Gentian mycorrhizae” also mycotrophic plants, but fungal partners are Glomeromycota mycotrophic associations with tropical plants (Gentianaceae) How do mycorrhizal relationships form? Specialized interaction between the plant and the fungus only certain fungi able to establish relationship with particular plant species EcM establishes soon after seed germination spores or contact with mycelium in soil Synchronized root growth and fungal hyphal differentiation fungi produce plant growth regulators that affect root morphology 1. Spores germinate, forming monokaryons root exudate promotes spore germination and growth 2. Monokaryons fuse (mating compatibilty) and form the dikaryon 3. Dikaryotic hyphae contact, recognize and adhere to root epidermal cells near the apex of young actively growing, lateral (feeder, fine) roots http://www.ffp.csiro.au/research/mycorrhiza/intro.html 4. mycelia proliferate on the root surface and form the mantle; http://www.ffp.csiro.au/research/mycorrhiza/intro.html 5. extension of hyphae from mantle into soil http://www.ffp.csiro.au/research/mycorrhiza/intro.html 6. hyphae penetrate root and colonize space between the cortex (conifers) and epidermal (angiosperms) cells to form the Hartig net http://www.ffp.csiro.au/research/mycorrhiza/intro.html http://www.ffp.csiro.au/research/mycorrhiza/intro.html 7. host responses may include polyphenol production in cells and deposition of secondary metabolites 8. active mycorrhizal zone occurs several mm behind the root tip 9. Hartig net • senesce in older regions further from the root tip • activity depends on the age of the root and rate of growth of root tip 10. Mantle: persists long after association become inactive • may function as storage structures and propagules Unique root growth and morphology • fungus secretes auxins, gibberellins, & cytokinins; plant growth regulators • enhances root growth and maintains juvenile roots; no root hairs • unique morphology for host-mycorrhizal fungus e.g., dicotomous branching in Pinus pinnate in Pseudotsuga plantbio.berkeley.edu/~bruns/ plantbio.berkeley.edu/~bruns/ Succession at the individual and stand levels Mycorrhizal fungi change during plant lifetime root may outgrow fungus and be colonized by another ectomycorrhizal fungus plantbio.berkeley.edu/~bruns/ a single tree will often have several mycorrhizal partners throughout its root system; it’s not one tree-one fungus as a forest ages different groups of ECM may dominate at different time points; early, late, & multi-stage the mycorrhizal fungi that are the major fruiting population may not be the dominant fungal mycorrhizal partner Some Ectomycorrhizal fungi Rhizopogon Boletus Boletus Cantherellus Laccaria Russula Ramaria Ramaria Thelephora Pisolithus AmanitaAmanita and Cortinarius Decay Pathogens in Western Forests • Natural disturbance agents • Host selective, have differential effect on different species of trees • Interact with other disturbance agents, e.g. fire, insects • Affect species composition, diversity • Indigenous pathogens are integral parts of ecological processes • Two general groups: root decay and stem decay Wood decay fungi in forests • Plants build complex structures from CO2, sunlight • Fungi deconstruct them to obtain C and energy for growth • Fungi are the major recyclers of C in all terrestrial systems • Plants have evolved complex structures, e.g. lignin, to resist degradation • Fungi have evolved various enzyme systems to decompose the range of naturally occurring substrates Cellulose Main component of plant cell walls, wood fibrillar structure based on β 1-4 glucose units occurs as crystalline regions intermixed with amorphous regions Cellbiose is a β 1-4 linked glucose disaccharide Enzymes of the cellulase complex 1, 4 β-D-glucan cellohydrobiohydrolase; cellobiohydrolase; exoglucanse cleaves cellobiose units from ends of celluose polymer 1, 4 β-D-glucan glucanohydrolase; endoglucanase randomly cuts internal bonds of amophous cellulose 1, 4 β-glucosidase; cellobiase hydrolyses cellobiose to glucose monomers Multiple forms (isoenzymes) are known Synthesis of cellulases is repressed by glucose, induced by cellulose, cellobiose Hemicellulose and pectin plant cell wall components, branching heteropolymer of mixtures of various monomers: glucose, galactose, mannose, arabinose, xylose Several different enzymes are needed for hemicellulose degradation e.g. xylanases Lignin degradation Lignin polymers of coniferyl, sinapyl alcohol, phenolpropanoid subunits Highly complex, irregular molecular structures Lignin monomers Lignin cometabolism Lignin a major component of plant cell walls, second in abundance to cellulose Only fungi are able to degrade lignin completely to CO2 Protects polysaccharide components from enzyme attack Lignin is degraded completely to CO2 by “white rot fungi” mostly basidiomycetes, Phanerochaete chrysosporium model system Not used as sole carbon source, not good source of energy Removed as other substrates are used—cometabolism an oxidative process, not hydrolysis does not release monomers as does cellulose decomp white rot decay extracellular enzymes, polyphenoloxidases (POD) low substrate specificity, oxidative attack produce free radicals Lignin peroxidase, LiP requires H2O2,veratryl alcohol (substrate of LiP) H2O2 is generated by several exoenzyme systems glyoxal oxidase LiP occurs as multiple isoenzymes generates free radical VA+ to remove electron from lignin PAH=polycyclic aromatic hydrocarbon 2+ Manganese peroxidase, MnP, similarly uses H2O2 to oxidize Mn to Mn3+, which then acts on phenolic substrates Glyoxal oxidase one of several oxidases that produce H2O2 Laccase a copper enzyme oxidizes phenolic molecules to quinines and quinones by single electron transfers Lignin oxidation by LiP requires H2O2 and veratryl alcohol Ectomycorrhizal Hymenomycetes Tremellales Trichosporonales Wood decay fungi Filobasidiales Cystofilobasidiales Dacrymycetales Auriculariales Gomphoid-phalloid Cantharelloid ectomycorrhizal fungi Hymenochaetoid Russuloid Thelephoroid Polyporoid Bolete Euagarics Blue bars are age estimate ranges, numbers in parentheses are mean age estimate, MYA Blue and red branches indicate significant expansion or contraction of polyphenoloxidases (POD). Numbers in red following taxon names are POD gene counts. The node labeled A is the ancestor of Agaricomycetes; nodes labeled B are “backbone” nodes in Agaricomycetes. Mean age of the Agaricomycetes (A) is ~290 MYA (million years ago) Ancestral Agaricomycete was a white rot fungus; brown rot and mycorrhizal species derived from white rot ancestors ca. 300 MYA, end of Carboniferous Period a sharp decline in organic carbon burial (coal)—a result of evolution of white rot fungi??? • The variety and complexity of fungal enzymes makes them useful for various applications: – remediation of contaminated soil – biofuels conversions – composting – industrial applications—pectinases, lipases, proteases, cellulases, laccases – fungal enzymes unique properties—activity, stability • The diversity of properties of fungal enzymes reflects their biodiversity and the diversity of habitats they inhabit • Fungi in natural habitats decompose dead organic matter, sapbrobes • Some decay fungi attack plants before they are dead, pathogens, parasites, necrotrophs Wood decay • Fungi break down wood • Recycle nutrients, add soil fertility • Creates nurse logs • Organic matter adds water- holding capacity to upper soil horizons • Forest regeneration • Tree species preferentially regenerate on decomposing logs, “nurse logs” Root decay pathogens Three major ones are basidiomycetes, Hymenomycetes Armillaria, Heterobasidion, Phellinus sporocarp a hymenophore (conk, mushroom) white rot fungi produce cellulases and polyphenoloxidases, enzymes that break down both cellulose and lignin brown rot fungi produce cellulases only; break down cellulose and leave behind lignin decomposed wood loses fibrous character brown, crumbly Laminated Root Rot Phellinus weirii (older name Poria weirii, other names Inonotus weirii? Hymenochaetaceae, Hymenochaetales Currently one species name covers two distinctly different pathogens; almost certainly two different species, but no one rushing to publish a new name On West side of Cascades: Douglas-fir form On Douglas-fir, Mountain hemlock, grand fir, laminated root rot On East side (Idaho, E. Washington) Western redcedar form on Western redcedar, “butt rot” Phellinus weirii laminated decay A white rot causing delamination of wood Aerial views of Phellinus weirii infection centers near Waldo Lake, OR Infection cycle of P. weirii • Stand replacing fire, kills dominant forest trees (Mt. hemlock) • Phellinus weirii remains alive, active in roots and CWD • Lodgepole pine for ca. 200 yr (not susceptible to LRR) • After 200-300 yr Mountain hemlock becomes dominant • Remnant mortality centers begin to appear and spread radially, sometimes merging • Based on annual rates of expansion, P. weirii genets conservatively estimated to be 1200-3000 years old, persisting over multiple overstory generations • >>Fungal pathogen is older than the dominant forest trees • >>Within mortality centers more species/structural diversity & complexity, uneven aged stands Phellinus weirii P. weirii can persist for many decades as a saprotroph Ectotrophic mycelium, spreads from colonized stumps & coarse woody debris to infect susceptible tree species Ectotrophic mycelium on roots Inside infection centers removal of overstory creates openings with different species (nonhosts), age mixture In