1. MODULE ADVANCED MICROBIOLOGY FUNGAL EVOLUTION by Gayuh Rahayu Microbiology Study Program Department of Biology Faculty of Mathematic and Natural Sciences Bogor Agricultural University 2010

2. Fungal Evolution The oldest fossils of eukaryotes dates back to 0.85 billion years ago, but whether any of these eukaryotes (Fig 1a) were fungi remains unknown. As the definitive fossil evidence are absence, we can only speculate the evolutionary sequence that led to the acquisition of those main features which distinguish fungi from other living creatures namely eukaryotic protoplasts, microfibrilar cell walls (Fig 1b) and mycelia morphology. Cell wall is the crucial structure in fungal evolution and also the bacteria (Fig 1c). The cell wall functions in the turgor pressure control, absorption of nutrition, protection towards plasmosptysis allowing a high concentration of intracellular metabolites and hence increased metabolism rates, survival and growth. Fig 1a) Relationship of Whittaker’s five kingdoms to the three major evolutionary lines based on adaptattion to three distinct mode of nutrition, b) Schematic comparison of basic structural elements of prokaryotic and eukaryotic cell wall, c) microfibrillar structure of a cysts wall of P. palmivora and d) isolated chitosomes from yeast cels of Mucor rouxii 1 b bdbd a c

3. The evolutionary success of the fungi may be attributed to the spreading and penetrating power of the mycelium. The mycelial habit made the fungi able to adapt and succeed as a unique evolutionary line in eukaryotic world. There are five distinctive phases in evolution of the fungal cell wall to understand when, how and why cell walls came into being (Fig 2). Cell wall is not essential to living cells, so we must consider them to have been absent from primitive biota. These primordial cells must have possessed three main features, 1) specific and efficient catalysts to make their own cell components, - proteins, 2) a central depository of information needed to make the catalyst – nucleic acids, and 3) a barrier to envelope catalysts and metabolites from the external surrounding –phospholipid/protein membrane. Cell walls was present in oldest known microfossils, bacterium in sediments 3.5 years old. Cell walls evolved rather rapidly after the appearance of the first living cells about 3.5 to 4 billion ago. The cell wall of the prokaryotes differ from the eukaryotes. The cell wall of prokaryotes is made from polimers (peptidoglican or murein, Fig 1b) suited to a high degree tensil strength. With a few exception, the wall of eukaryotes have a microfibrillar structure (Fig 1c).For the fungi, the microfibrillar structure is made of khitin (Fig 1 b) kept in chitosome (Fig 1 d). From the lowest to the highest members of plant and fungal kingdoms, the same basic architecture of the wall is a skeleton of interwoven microfibrils embedded in amorphous matrix. Whether the cell wall of the eukaryota originate from the cell wall of prokaryotes or the eukaryotes developed from naked protoplast is still unclear (Fig 2). Fig 2. The most reasonable stages in the evolution of fungal cell walls Composition of the cell wall of the fungi are different (Fig 3). The primary component of the cell wall of true-fungi is chitin, whilst those of pseudo-fungi is cellulose. This has been effected the 2

4. 3 systematic of the fungi. The true-fungi are placed in the kingdom Fungi and the psudo-fungi are placed in Kingdom Chromista or Stramenophilla. The wall-less Fungi are placed in Kingdom Protozoa or Protoctista (Fig 5) Fig 3. Structural cell wall polysaccharides Fig. 4 Phylogenetic tree of the kingdom Fungi

5. 4 The Origin of True-Fungi and Chytrids Fungi are closer to the animals than to the plants with repects to 1) both commonly have chitinuous exoskeletons, 2) both store glycogen not starch, 3) both lack chloroplasts and iv) unlike plants, their mitochondrial codes, UGA codes for trypthophan, not chain termination (Fig.4). Chytridiomycetes have two other key features that narrow the search for their ancestor. The features are a single posterior cilium on the motile cells flattened and, non discoidal cristae (Fig 5). Only two other eukaryote groups have both character, i.e. metazoan and chanoflaggelates. To convert choanoflagellates to chytrids acquires a chitinous wall and lose phagotrophy (Fig. 6). Most likely the ancestral of chytridiomycetes are the Spizellomycetales (Fig. 7). Their zoospores seem primitive in 3 respects : 1) they are the only one with ribosomes dispersed in the cytoplasm as in most protists (other chytridiomycetes have a nuclear cap of ribosomes and therefore derived, not ancestral, 2) they are more amoeboid and 3) in some, the non-ciliated centriole is about 90 0 to the ciliated one, as in animals and choanoflagellates. Fig. 5 Phylogenetic relationship of the fungi

6. Spizellomycetales might be the ancestral form of Chytridiomycetes from which Blastocladiales and Chytridiales give rise independently. While Monoblepharidales probably evolved from Chytridiales. The ciliary roots of some Spizellomycetes resemble Choanociliates. Further, fan- shaped arrays of microtubules diverge from arc-like dense bodies beside the kinetosome and the narrow end of the fan is cross-striated. Fig. 6. Origin of the first fungus from a thecae choanociliate. A) life cycle of a thecae choanociliate (Salpingoecidae). B) an epiphytic salpingoecid undergoes a mutation, sticking its apical rather than basal end to the algal surface, so that thecal secretion prevents it from I) feeding phagotropically; II) survival would depend on either saprophytism or III) parasitism, with loss of collar and cilium, the theca would become complete wall and dispersal form of the choanaciliate (V) is retained. K L N R m nfc er = kinetosome = lipid body = nucleus = ribosome = mitochondria = non-functional centriole = endoplasmic reticulum Fig. 7 Zoospores of Spizellomycetales ultrastructure. 5

7. 6 The origin of zygomycetes Zygomycetes has non-flagellate spore and posses zygospores. These characters differentiate the zygomycetes from chytrids. To convert chytrids to zygomycetes, the zoopores should lose the flagella. Of the chytrids, Allomyces (Allomycetales) is most likely ancestors of zygomycetes that convert to the most primitive zygomycetes, the Basidiobolus (Entomophorales, Fig 8). Allomyces is typically coenocytic and lack dictyosome. Their mitosis closed with centriole outside the nucleus. This is probably a pre-adapted to ciliary lost. Fig. 8 Allomyces (Allomycetales), the most likely ancestors of zygomycetes (left) and the most primitive zygomycetes, Basdiobolus (Entomopho-rales, right), A-C) spore formation and release, D) spore on insect, E) zigospore with clamp The origin of ascomycetes The Hemiascomycetes and Euascomycetes may evolve in different line with different ancestor of zygomycetes. The ascomycota can be simply derived from zygomycete group Endogonales (Fig. 9). Only two significant modifications are needed to convert the subterranean endogonalean sporocarp into plectomycetes ascocarp (Plectomycetes) i.e. i) evolution ofd endospores from zygospores to ascospores and ii) evolution of ascogenous hyphae. The other three classes Loculoascommycetes, Pyrenomycetes and Discomycetes migt evolved independently from an early plectomycete by mutation that spread the ascospores more efficiently, the Loculoascommycetes involving active spore discharge by bitunicate asci, the Pyrenomycetes with pen perithecia or with apothecium in Discomycetes (Fig 10). The Hemiascomycetes might also evolve from the entomophoralean zygomycetes such as Completoria.

8. 7 Fig. 9 Endogone (Endogonales) ancestor of ascomycetes The origin of basidiomycetes Fig 10. Proposed phylogeny for Basidiomycota Basidiomycota differ from ascomycota in two respects: their post-meiotic spores (exospores) not endospores and they have a vegetative heterokaryophase. The basidia and asci have a similar function that equally well such that there is no advantages to change over. Developmentally it is easy for entomophoralean conidia to form basidia. Basidiospores are formed by conidia-like

9. 8 budding of the presumptive spores and their separation from the metabasidium by sterigmal septa. Entomophorales typically has actively discharge conidia and key changes to change into basidiomycetes i.e i) modification of the drop spore discharge mechanism and ii) by suppression of nuclear fusion in zygospores. Thus the basidiomycetes ancestral might have either zygospores or basidiospores such as in Teliomycetes. Teliosporesis just like zygospores, a premeotic struscture, but teliospores differ from zygospores in not being immediate product of hyphal fussion. Teliospores is formed from uredinisopres whih from from nuclear syngamy that developed just like pre-condiniation, thus possibily the same process of zygospores formation. The teliospores in the Urediniales might be derived, but it may be reversion to an ancestral types. The septation of teliomycetes metabasidia support their derivation from vegetative conidiophores. Similarly, the metabasidia of Auriculariales and Septobasidiales, they have long metabasidia suggested they derived from teliomycetes. The fundamental cleavage is between Urediniomycotina and orthomycotina which diverge in centrosome diversification. The evolution of the rest of basidiomycetes is in Fig 10. Questions: 1. Describe the characteristic of common ancestor of eufungi! ( max 7 sentences) 2. How did the zygosmycetes evolve to ascomycetes ? 3. Is there any possibility of basidiomycetes to derive from ascomycetes ancestor? Give a short explanation. References: Alexopoulos C.J., C.W. Mims dan M. Blackwell. 1996. Introductory Mycology. 4 th ed. New York: John Wiley & Sons, Inc. Cavalier-Smith. T. The origin of Fungi and Psudofungi. 1987 in Rayner,ADM, CM Brasier and D. Moore (eds). Evolutionary Biology of the Fungi. Cambridge: Cambridge University Press. P 339=354 More-Landecker, E. 1996. Fundamentals of the Fungi. 4 th ed. New Jersey: Prentice Hall.