“Zygomycota”

1. “Zygomycota” Kingdom Fungi

2. “Zygomycota” • Is polyphyletic & has been divided into four subphyla • Vegetative stage – well developed aseptate hyphae • Asexual reproduction by nonmotile sporangiospores • Sexual reproduction – Zygospore produced in a zygosporangium from fusion of two similar gametangia • Ca. 800 spp.

3. “Zygomycota” • Will discuss two major orders in two of the subphyla and mention the Trichomycetes in a third • Mucorales – saprotrophic (420 spp) • Entomophthorales – parasites of arthropods (240 spp) • Trichomycetes - Harpellales & Asellariales smaller (135 spp), less well understood, are commensals on surface and in guts of arthropods

4. Mucorales • Zygospore production is generally similar among species, therefore classification is based on characteristics of asexual reproductive structures • Asexual reproduction is typically by production of sporangiospores, but we will see lines of evolution in which the number of spores/sporangium is reduced until there is only 1 spore/sporangium - conidium

5. Mucorales • Grow saprotrophically on decaying plant and animal remains in soils, dung, etc. • Produce large numbers of asexual spores that are dispersed in the air • Common contaminants in laboratory • Some are important in spoiling food – common bread mold, storage diseases of fruits and vegetables • Some infect humans and animals – opportunistic pathogens

6. Mucorales • Typically form aseptate hyphae, septa formed to delimit reproductive structures • Some species form rhizoids • Rhizoids – generally tapering structures without nuclei

7. Multispored sporangium • Morphology of sporangia varies, basis for classification • Typical multispored sporangium contains • Sporangium wall • Sporangiophore – modified hypha that supports the sporangium • Columella – extension of sporangiophore into the sporangium

8. Development of sporangium • Tip of sporangiophore swells • Swelling increases, contains multinucleate cytoplasm • Cytoplasm is cleaved to form all spores at one time – cell membrane and cell walls laid down around nuclei

9. Development of sporangia • After formation, sporangial wall may break and release spores into the air or • A drop of fluid may envelop the sporangium with spores being dispersed by small animals that touch the sporangium

10. Reduction of sporangium • Several lines of evolution in the reduction of number of spores/sporangium • Examples of modifications of sporangia • Thamnidium – both multispored sporangium and smaller sporangia = sporangiola

11. Reduction of sporangia • Blakeslea – sporangiola with 3 spores/sporangiolum • Cunninghamella – one spore/sporangiolum, spore wall and sporangiolum wall indisdistinguishable except with EM

12. Reduction of sporangia • One group in the Mucorales produce cylindrical sporangia = merosporangia • Also see a reduction in the number of spores/sporangium in this line • Syncephalastrum

13. Other sporangial modifications • Pilobolus – fungal shotgun • Grows on herbivore dung • Sporangiophore contains carotenoids, acts as a lens to focus light and direct the growth of the sporangiophore to point the sporangium at light source

14. Pilobolus • As the sporangium and sporangiophore mature, the sporangiophore builds up a very high turgor pressure • Sporangium as a whole is shot off suddenly, directly at the light – up to 3 m • A drop of fluid on the sporangium causes it to stick to whatever it hits • Phototrophic ability allows sporangium to be shot out of a pile of dung, land on grass, be eaten by herbivores

15. Pilobolus • Passage through gut of herbivore activates spore germination • Sporangium is dark in color to prevent damage from UV when attached to grass

16. Sexual Reproduction • Gametangium – haploid multinucleate structure that typically produces gametes • Gametes – haploid cells that are involved in fusing (plasmogamy), e.g. eggs and sperm • In some fungi, gametangia do not produce gametes but fuse themselves

17. Sexual Reproduction • Fungi may produce gametes in gametangia or they may produce gametangia without gametes • In some fungi, gametes, gametangia may fuse with other gametes, gametangia from the same thallus = homothallic • In other fungi, gametes, gametangia from one thallus are prevented from fusing with others from the same thallus = heterothallic • Variety of genetic factors control heterothallism

18. Sexual reproduction in Zygomycota • Involves fusion of two multinucleate haploid gametangia that are similar in structure, may differ in size • Gametangia are produced as terminal swellings of hyphal branches • After plasmogamy – a thick walled zygospore is produced within a zygosporangium • Both homothallic and heterothallic species

19. Life cycle • Vegetative mycelium is haploid, reproduces asexually by producing sporangiospores in sporangia • In a heterothallic species, when two compatible strains (+ and -) come together, hyphal branches form, enlarge to form progametangia

20. Life cycle • Two hyphae come together and swell producing progametangia • Septa form, producing multinucleate gametangia and suspensors • Gametangia fuse and form zygospore

21. Life cycle • Plasmogamy occurs, end walls of gametangia dissolve and cytoplasm of gametangia mixes • Multinucleate zygospore is formed

22. Formation of zygospore

23. Life cycle • Zygospore develops thick wall, warty appearance, dark in color • Karyogamy occurs at different times in zygospore formation in different species, so zygospore is diploid at some point

24. Life cycle • When zygospore germinates, meiosis occurs to start the haploid portion of the life cycle over again

25. Life cycle

26. Variation in zygospores • Some variation is seen in zygospore formation

27. Entomophthorales • Arthropod parasites, 240 spp. • Asexual reproduction by one spored sporangiola (conidia) • Mycelium exhibits limited growth in the body of the host, forms septa and fragments • Entomophthora is a parasite of flies – seen when fly is stuck to window, white halo around it

28. Entomophthora • Mycelium fills up body of fly, forms sporangiophores that extend out of segments of abdomen

29. Entomophthora • Sporangiophore builds up pressure, shoots off sporangiolum when there is air movement (another fly) • If misses, can form another structure that shoots it off, up to 3 times • Sexual reproduction not well understood, form resting spores that are similar to zygospores

30. Entomophthorales

31. Trichomycetes • All but a few species are obligate commensals in guts or on exoskeleton of arthropods • Found in freshwater (mayfly, stonefly, midges) and terrestrial (millipedes) arthropods

32. Trichomycetes • Thallus is relatively simple – produce a holdfast that anchors them to lining of gut

33. Trichomycetes • Thallus may be unbranched and aseptate or branched and septate • Variety of asexual spores produced (generally 1 spore/sporangium)

34. Trichomycetes • Sexual reproduction involves formation of zygospores (in one order) • Fusion of cells in thallus • Formation of zygosporophore and then zygospore

35. Glomeromycota • These fungi were once placed in the Zygomycota, now a separate phylum • Obligate biotrophs • Biotrophic in the roots of higher plants (ca. 80%), form arbuscular mycorrhizae • Ca. 169 spp.

36. Glomeromycota • Form tree-like structures = arbuscules in cells of plant – exchange of nutrients between fungus and plant • Form large spores in soil –azygospores, and chlamydospores depending on species

37. Glomeromycota • Spores are large, 40-800 µm in diameter • We will discuss these fungi more in mycorrhizae

38. Phylogenetic relationships