Phylum - Ascomycota

1. Phylum - Ascomycota Kingdom - Fungi

2. Higher fungi • Two phyla – Ascomycota and Basidiomycota • Thallus in both consists of sepatate hyphae that form extensive mycelia • Septa have pores that allow migration of cytoplasm, organelles and nuclei (specialized septa in Basidiomycota) • Compartments contain multiple nuclei

3. Higher fungi • Vegetative hyphae can fuse with one another = anastomosis (does not occur in lower fungi) • Asexual reproduction by conidia on conidiophores

4. Higher fungi • In sexual cycle, plasmogamy is separated from karyogamy – produces dikaryotic phase • Most of these fungi produce multicellular fruiting bodies • In general, called: • Ascoma (ascomata) in Ascomycota • Basidioma (basidiomata) in Basidiomycota

5. Higher fungi • Sexual reproduction produces spores after meiosis – ascospores or basidiospores (1n)

6. Ascomycota • General characterisitics • Generally have a similar sexual life cycle • All produce an ascus (sac-like structure) that contains haploid (1n) ascospores after meiosis • Includes ~75% of the described fungi – 64,000 spp. (20,000 anamorphs)

7. Ascomycota • Sexual life cycle is basically similar – haploid-dikaryotic life cycle • Vegetative phase is haploid mycelium that may reproduce asexually by formation of conidia • Plasmogamy is separated from karyogamy in time so that a dikaryotic phase is produced – the ascogenous hyphae represent the dikaryotic hyphae

8. Gametangia • Male gametangia may be an antheridium or conidium-like structure – spermatium • Female gametangium = ascogonium, may have a long projection, the trichogyne

9. Gametangia

10. Plasmogamy • Male element fuses with trichogyne of the ascogonium, nuclei migrate into the ascogonium to begin the dikaryotic condition • After plasmogamy, two hyphal systems begin to grow • Sterile haploid hyphae envelope the ascogonium to form the multicellular ascoma (fruiting body) • Dikaryotic ascogenous hyphae grow from ascogonium – will give rise to the asci

11. Ascogenous hyphae • Male and female nuclei divide conjugately to maintain the dikaryotic condition • Many ascogenous hyphae produced inside the developing ascoma • Tips of ascogenous hyphae form croziers (hooks) before developing into an ascus

12. Developing ascoma • Ascoma contains two types of hyphae • Ascogenous hyphae – dikaryotic, form asci through crozier formation • Sterile hyphae – haploid, form bulk of ascoma

13. Crozier and ascus formation • During ascus formation, karyogamy occurs to form a diploid nucleus followed by meiosis to form 4 haploid nuclei Mitosis Meiosis Karyogamy

14. Ascus formation • Most asci are cylindrical, but may be globose • 8 ascospores/ascus is a common number but this may vary • In most, ascogenous hyphae continue to proliferate, forming more croziers and more asci

15. Types of asci • Great deal of variation in asci and ascospores • Three basic types of asci • Prototunicate asci – thin, delicate wall that deliqueses to release ascospores

16. Types of asci • Unitunicate asci – ascus wall layers adhere closely to one another, ascospores released through a pore, a slit or an operculum (hinged cap) • Operculate asci • Inoperculate asci

17. Types of asci • Bitunicate asci – two wall layers that separate with the inner wall expanding, ascospores released through a pore

18. Fruiting bodies - ascomata • In most, the ascogenous hyphae are produced only in the ascoma (pl. ascomata • Ascomata consist of two types of hyphae – dikaryotic ascogenous hyphae that form the asci and haploid sterile hyphae that form the bulk of the ascoma • Four major types of ascomata

19. Cleistothecium • The cleistothecium remain closed until broken by internal forces, the asci are produced randomly within the ascoma

20. Perithecium • Begins as a closed structure but produces a pore at maturity through which the ascospores can escape • Asci produced in a definite layer - hymenium

21. Apothecium • Ascoma is open when asci mature, asci are produced in an hymenium

22. Ascostroma • Asci are produced in a cavity (locule) within a mass of sterile tissue = stroma • No ascoma wall as stroma did not originate from ascogonium

23. Ascomycota classification • Currently in a state of flux • The most current treatment divides the Ascomycota into three subphyla • Pezizomycotina – the largest is divided into 10 classes • Saccharomycotina – yeasts • Taphrinomycotina – yeast-like • 43 (35) orders have been proposed in the Ascomycota, some of these only contain lichens

24. Pezizomycotina • We will examine these fungi as: • Cleistothecial Ascomycota • Perithecial Ascomycota • Apothecial Ascomycota • Pseudothecial Ascomycota • Will discuss representatives within each of these groups to get an introduction to the Ascomycota

25. Cleistothecial Ascomycota • Cleistothecia are the simplest type of ascoma • Surrounded by relatively simple tissue (loose hyphae), do not have an opening, are broken open • Asci are scattered • Asci are prototunicate, globose to pear shaped

26. Cleistothecial Ascomycota • Include species that grow as saprotrophs on keratin (protein in hair, nails) • Contains the teleomorphs of human pathogens • Dermatophytes – cause superficial skin infections such as atheletes foot • Anamorphs are Trichophyton and Microsporium • Also contains fungi that cause deep or systemic infections of humans • Ajellomyces, the teleomorph of Histoplasma capsulatum which causes histoplasmosis • Blastomyces which causes blastomycosis

27. Aspergillus & Penicillium • The anamorphic stages (Aspergillus and Penicillium) – better known than the teleomorphs • Asci are spherical to club shaped, ascus wall dissolves at maturity leaving ascospores free inside the cleistothecium • Most are saprotrophs • Widespread in soil, litter • Opportunistic human & animal pathogens – aspergilloses, penicilloses

28. Aspergillus & Penicillium • Important industrial organisms, used in making – • Chemicals – citric, gluconic & other organic acids • Antibiotics – penicillin, griseofulvin • Production of miso and soy sauce, sake • Cheese production – blue cheese and camembert • Also important in food spoilage • Citrus fruits • Grains & peanuts – produce mycotoxins

29. Aspergillus • Anamorphic genus – close to 100 species • 11 different teleomorphic genera produce Aspergillus conidia and conidiophores, including Eurotium, Emericella • Common fungi found in air, soil, water • Grow on a variety of substrates, in humid climates found growing on clothing, shoes, etc. • Important as contaminants of stored grain, species produce aflatoxin

30. Aspergillus • Produce characteristic conidiophore • Conidia produced by phialides – flask shaped conidiogenous cells • Have a characterisitic foot cell

31. Penicillium • Over 95 species connected to 3 teleomorphic genera – Talaromyces, Eupenicillium, Carpentales • Very common in soil, conidia found in air, water, soil • Food spoilage – on citrus fruits, jelly, cheeses • Produce penicillin and other chemicals industrially • P. roqfertii, P. camembertii used to make cheeses

32. Penicillium • Asexual conidiophore – not swollen at tip, no foot cell • Phialides arranged in a brushlike manner

33. Powdery mildews • Ascomata do not form opening so can be termed cleistothecia, but are more like perithecia without an opening • Asci occur in an irregular layer, not scattered • Asci are unitunicate, forcibly discharge ascospores through a slit • Produce colorless hyphae on surface of plant host • Produce haustoria that penetrate epidermal cells of host

34. Asexual reproduction • Hyphae produce chains of conidia during growing season (spring and summer) on surface of plant leaf – giving the powdery, white appearance

35. Sexual reproduction • Late in growing season, as plants begin to senesce, ascomata are produced – thought to overwinter as ascomata • Ascomata are closed, have characteristic appendages extending from them • Asci are globose to ovoid, generally one to a few asci/ascoma

36. Ascoma • Appendages

37. Perithecial Ascomycota • Ascoma is a perithecium • Has an opening through which ascospores leave the ascoma = ostiole • Asci produced in a layer = hymenium • Asci are unitunicate and inoperculate • Asci typically have a pore or slit at the thickened tip

38. Perithecial Ascomycota • A large and diverse group of fungi –(have already discussed the powdery mildews which are sometimes included here • Include species which are • Saprotrophs – wood, dung, soil, plant litter • Parasites – plant, animal (arthropod) diseases • Endophytes • Some produce mycotoxins • One species used as a meat substitute

39. Perithecia • Typically flask shaped structures • Pore with opening = ostiole • Perithecial wall composed of pseudoparenchyma tissue • Centrum is the central part where asci develop

40. Perithecia • Perithecial wall composed of fungal tissue called pseudoparenchyma – thin cell walls, looks like plant parenchyma tissue • Centrum – the asci and sterile structures that fill the cavity within the perithecial wall • Sterile structures: • Paraphyses – basally produced in hymenium • Pseudoparaphyses – originate from top of the perithecium, grow into hymenium • Periphyses – extending into the ostiole

41. Perithecium Ostiole Periphysis • Classification is based in large part on development of centrum, development of paraphyses or pseudoparaphyses Wall Stroma Paraphysis Ascus Ascospore

42. Perithecia • Perithecia may be produced individually or they may be produced within a mass of tissue = stroma (always produce a separate perithecial wall)

43. Stroma (stromata) • Compact tissue that forms a flat plate or a mass • Hyphae may be inflated, intertwined, have lost identity to form a tissue that looks like parenchyma tissue of plants – called pseudoparenchyma • May be hard and woody or soft and fleshy

44. Perithecial Ascomycota • Saprotrophic fungi on dung, wood, in soil & decaying leaves • Includes Neurospora – important in study of genetics • Asci are club shaped to cylindrical, most produce 8 ascospores • Asci may breakdown and release ascospores or persist & forcibly discharge ascospores

45. Chaetomium • Common saprotrophs in soil and dung, highly cellulolytic • Perithecia have distinctive filaments (straight or spiral )extending from upper part of perithecium • Asci are club shaped and wall deliqueses leaving ascospores embedded in jelly like substance that oozes out of the ostiole

46. Chaetomium • Ascospores are lemon shaped

47. Neurospora crassa • Red (pink) bread mold – grows on dough in bakeries, forms lots of conidia, bad contaminant • Widely used in genetic studies, one gene – one enzyme concept developed in Neurospora • Mostspecies are heterothallic – two mating types – A & a

48. Sordaria perithecia & asci

49. Ascospore discharge • In many Ascomycota, asci develop high turgor pressure and actively discharge ascospores individually or as a group from ascus • In some, particularly coprophilous forms, the asci or ascomata may be phototrophic so that ascospores are discharged toward the light

50. Ascospore discharge • In Sordaria, Neurospora and other members of this group, asci stretch through ostiole and actively discharge ascospores