Fungal Growth and Sporulation

G. T. Cole. 1986. Microbiol. Rev. 50: 95-132

From: Fischer-Parton et al. 2000. J. Microscopy 198 (3): 246-259 Exocytosis—enzymes (pectinases, cellulases, proteases) to degrade compounds in the environment Endocytosis—removal of excess plasma membrane, recycling membrane proteins, transport of membrane proteins & lipids to vacuole for degradation, uptake of molecules, etc.

? Mannoproteins Glucan synthase Wall-lytic enzymes, protease activators Chitosomes (chitin synthase) Multivesicular bodies Wall substrates Enzyme activators (GTP), inhibitor Delivered from cytosol? Components probably delivered by membrane-bound vesicles plasmalemma wall Components of wall synthesis at hyphal tip. Modified from Deacon (2006). Fungal Biology.

Asexual Sporulation Sporangiospores formed by cleavage of protoplasm in a multinucleate sporangium (Chytridiomycota, Zygomycota, Oomycota) Conidia develop directly from hyphae or from modified hyphal cells called conidiogenous cells (Ascomycota including Deuteromycetes, some Basidiomycota)

Control of asexual sporulation May be triggered by changes in carbon:nitrogen ratio in growth medium May require light trigger, e.g. near-ultraviolet light Under control of sporulation genes: One group involved in switch from somatic growth to sporulation A second group regulates developmental stages of sporulation A third group regulates secondary aspects including spore color

Asexual Fungi: Deuteromycetes

Deuteromycetes “deuter-” Gk., meaning “second” > 20,000 species of fungi in 2600 genera have no known sexual state Most belong in phylum Ascomycota These fungi are also called: Anamorphic fungi Mitosporic fungi Conidial fungi Imperfect fungi Fungi imperfecti

Asexual propagules Chlamydospore Sclerotium (pl. sclerotia) 1-celled spore (usually thick-walled) designed for perennation; formed inside existing cell Sclerotium (pl. sclerotia) Rounded mass of hyphae, often differentiated into rind and medulla

Asexual propagules Conidium (pl. conidia) Non-motile spore designed for dispersal Wide range of shape, size, color and septation among taxa

Saccardoan Spore Types P.A. Saccardo (1845-1920) “Sylloge Fungorum” (1882-1972)--names & descriptions of all known fungi Developed system of classifying fungi based on type of spore (shape, septation, color)

Saccardoan Spore Types Color Hyaline or bright (hyalo-) Pigmented (phaeo-) Shape and septation 1-celled—amerospore 2-celled—didymospore Multicelled—phragmospore Muriform—dictyospore Filiform—scolecospore Helical—helicospore Branched--staurospore

Saccardoan Spore Types scolecospore amerospore staurospore helicospore dictyospore phragmospore didymospore

Synanamorph Two or more types of asexual spores formed by the same fungus Example: Ceratocystis fibriata

Conidiogenous Cells A cell that forms one or more conidia May be formed on a specialized simple or branched hypha called a conidiophore

From D. Malloch

Conidial Development (Ontogeny) Blastic—blowing out of conidial initial prior to formation of delimiting septum Thallic—conversion of segment of existing hyphae into conidia

Blastic versus thallic Cole, 1986

Blastic development Holoblastic Enteroblastic single conidium is formed from conidiogenous locus, all wall layers involved in formation of conidium wall Enteroblastic more than one conidium formed from locus, only the inner wall layer(s) involved in formation of conidium wall

Holoblastic From Hawksworth et al., 1995

Holoblastic/synchronous Holoblastic/sympodial From Hawksworth et al., 1995

Enteroblastic development Phialidic—a basipetal succession of conidia is formed from a fixed locus on the conidiogenous cell (phialide) collarette

Enteroblastic development Annellidic—a basipetal succession of conidia formed by repeated percurrent proliferation of conidiogenous locus, leaving the distal end of locus with transverse scars (annellations)

Enteroblastic development Tretic—the inner wall of the conidiogenous cell blows out through a hole (pore) in the outer wall like a balloon to form a conidium.

Arrangement of conidia at locus Solitary  Catenate = true chains Seriate = false chains, spore heads Dry spores Wet spores (gleoid)

Succession of conidia Basipetal = a chain of conidia in which new spores are formed at the base, the oldest conidia are at the apex Acropetal = a chain of conidia with the new spores formed at the end of the chain, oldest spores are at the base. In order for this type of conidial formation to occur, the conidia must function as conidiogenous cells (e.g., Alternaria, Cladosporium)

Alternaria conidiogenous cells and conidia

Alternaria

Cladosporium; arrows indicate pores (tretic conidial development)

Conidiophores Hyphae bearing conidiogenous cells Morphologically differentiated from vegetative hyphae (=macronematous) Morphologically not differentiated (=micronematous)

Conidiophores

Types of Deuteromycetes Hyphomycetes—fungi that produce conidia from conidiogenous cells free on their mycelia May be formed on the surface of synnemata or sporodochia Coelomycetes—fungi that produce conidia from conidiogenous cells formed in conidiomata

Synnemata Conidiophores united at base Conidiogenous cells at apex

Sporodochium A compact, cushion-like aggregation of hyphae on which conidiophores are formed in a dense layer The aggregation of hyphae is called a stroma (pl. stromata)

Hyphomycetes Moniliaceae—conidiophores formed singly, hyphae and conidia pale-colored Dematiaceae—conidiophores formed singly, hyphae and/or conidia dark-colored Tuberculariaceae—conidiophores aggregated on cushion-like sporodochium (pl. sporodochia) Stilbaceae—conidiophores aggregated in a synnema (pl. synnemata), an erect bundle with conidia formed at apex