Thallus Development in the Chytridiomycota

Transcription

1 Thallus Development in the Chytridiomycota Rabern Simmons, PEET trainee University of Maine Mycological Society of America Annual Meeting July 29, 2009

2 Purpose Provide a glossary for teachers and students of the Chytridiomycota, or chytrids Slightly different vocabulary than other fungal groups Allow students to accurately explain what they see Provide coherent discourse of ideas

3 To meaningfully construct this glossary... Define morphological terms Show examples and compare morphologies Show evidence that similarity of form does not necessitate relatedness Morphological trends occur in multiple lineages

4 Chytridiomycota True fungi that produce zoospores with single smooth, posterior flagellum Molecular phylogenies hypothesize 2 classes Monoblepharidomycetes 1 order Chytridiomycetes 6 described orders 3 clades with no ordinal description

5 Traditional Morphological Taxonomy Characters viewed by light microscopy (LM) Possession of operculum Lid-like portion of zoosporangium Amount of thallus devoted to zoosporangium Development of zoosporangium from zoospore cyst Number of zoosporangia per thallus

6 I. Thallus Morphology Holocarpic Eucarpic Olpidium sp. (currently incertae sedis) Most common chytrid form. Sparrow, Aquatic Phycomycetes.

7 Holocarpic chytrid Zoosporangia with zoospore discharge tubes Plant cell wall Resting sporangia of fungus Olpidium brassicae in root cells (LM). Used with permission of D J S Barr.

8 Eucarpic chytrids Rhizoids Defining feature Robust and blunt-ended Sparse, fine and tapered Isodiametric... Just to name a few.

9 Rhizoids May have subsporangial swelling, or apophysis Chytriomyces aureus on chitin (Hoffman modulation contrast LM) JEL72 Unidentified Cladochytriales on agar (phase contrast LM) Unidentified Spizellomycetales on agar (LM)

10 II. Development of the Zoospore Cyst Endogenous Exogenous Zoospore cyst JEL369 Clydaea vesicula on agar (phase contrast LM) Barr81 Powellomyces hirtus on agar (Hoffman modulation contrast LM)

11 Endogenous Growth: Swelling of zoospore cyst Zoospore with flagellum Rhizoidal axis JEL539 Maunachytrium keaense on agar (phase contrast LM)

12 Exogenous Growth: Nuclear migration Zoospore cyst (zc) Zoosporangium zc zc Rhizoidal axis JEL129 Entophlyctis luteolus on agar (phase contrast LM)

13 Exogenous-Endogenous Growth e.g. Blyttiomyces helicus Cytoplasm initially exits zoospore cyst into germ tube Zoospore cyst Exogenous development Cytoplasm re-enters zoospore cyst during maturation of zoosporangium Endogenous development

14 Blyttiomyces helicus Apiculus: Apex of initial zoospore cyst On spruce pollen (LM)

15 III. Number of zoosporangia Monocentric Polycentric Zoosporangium Papilla Rhizoids Rhizomycelium Rhizoids JEL 95 Powellomyces sp. on agar (Hoffman modulation contrast LM) Zoosporangia JEL109 Polychytrium aggregatum on agar (phase contrast LM)

16 Monocentric Chytrids Holocarpic or Eucarpic Endogenous or Exogenous Many Chytridiomycetes Select Monoblepharidomycetes Holdfast anchor to substrate Loss of flagellum

17 Monocentric Monoblepharidomycete with holdfast Harpochytrium hedinii on agar (phase contrast LM) Emerson & Whisler Cultural studies on Oedogoniomyces and Harpochytrium, and a proposal to place them in a new order of aquatic phycomycetes.

18 Monocentric, Holocarpic Monoblepharidomycete Previous cell wall Hyaloraphidium curvatum on agar (phase contrast LM)

19 Polycentric chytrids Giving rise to multiple zoosporangia Eucarpic and Exogenous Rare exceptions Several Chytridiomycetes Majority of Monoblepharidomycetes

20 Polycentric Chytrids Rhizomycelium is coenocytic or rarely septate JEL109 Polychytrium aggregatum on agar (phase contrast LM) JEL610 Cladochytrium sp. on agar (phase contrast LM)

21 Pseudosepta in Gonapodya sp. (Monoblepharidomycetes) Gonapodya polymorpha on agar (phase contrast LM)

22 Polycentricity continued Terminal or intercalary zoosporangia & swellings JEL109 Polychytrium aggregatum on agar (phase contrast LM) M53 Monoblepharis sp. On agar (phase contrast LM) JEL611 Nowakowskiella sp. on agar (phase contrast LM)

23 More polycentrics on agar JEL137 Physocladia obscura JEL342 Catenomyces persicinus M36 Gonapodya polymorpha M6 Gonapodya prolifera

24 Polycentric Monoblepharidomycete w/ holdfast & w/o rhizomycelium Oedogoniomyces spp. on agar (phase contrast LM) Emerson & Whisler Cultural studies on Oedogoniomyces and Harpochytrium, and a proposal to place them in a new order of aquatic phycomycetes.

25 Problems with morphological taxonomy 1. Morphology in situ not necessarily the same as pure culture

26 Lobulomyces poculatus eucarpic, endogenous, monocentric Veil of cell wall Veil may be absent Empty zoosporangium with operculum on spruce pollen (phase contrast LM) Developing zoosporangium on agar (phase contrast LM)

27 Problems with morphological taxonomy 1. Morphology in situ not necessarily the same as pure culture 2. Morphology may differ on various nutrient media

28 JEL95 Powellomyces sp. eucarpic, monocentric, generally exogenous zc zc zc zc? on agar (Hoffman modulation contrast LM)

29 Problems with morphological taxonomy 1. Morphology in situ not necessarily the same as pure culture 2. Morphology may differ on various nutrient media 3. Morphology is not indicative of phylogeny

30 Example 1: Molecular clades with known monocentric exogenous development Tree adapted from James et al A molecular phylogeny of the flagellated fungi (Chytridiomycota) and description of a new phylum (Blastocladiomycota).

31 Example 2: Molecular clades with known polycentric growth Tree adapted from James et al A molecular phylogeny of the flagellated fungi (Chytridiomycota) and description of a new phylum (Blastocladiomycota).

32 Conclusions Large degree of variation seen in simple, basal fungi Makes them interesting, but difficult to explain Morphology remains useful for species identification L. poculatus, B. helicus, etc. However, morphological similarity is not necessarily an indication of relatedness Must emphasize, or else we are defining but not educating!!!