Phylogeny of the Zygomycota based on nuclear ribosomal sequence data
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F IG . 1. Phylogeny of Zygomycota based on rRNA operon (18S+28S+5.8S genes). Shown is a majority-rule consensus phylogram computed from the set of 36 000 credible trees with branch lengths averaged over trees. Numbers above branches indicate nodes that were supported by $ 95% Bayesian posterior probability. Branches supported by parsimony bootstrap $ 70% are indicated by thickened lines. Hashed lines indicate long branches divided by 8 to improve visibility of branch lengths. W HITE ET AL : P HYLOGENY OF THE Z YGOMYCOTA 875 (Gehrig et al 1996, Jensen et al 1998), the Ascomycota + Basidiomycota (Helgason et al 2003) or their relationships were unresolved (Bruns et al 1992, Tanabe et al 2000). Phylogenetic relationships of the Mucorales also were unresolved in a Bayesian SSU+LSU two-locus phylogeny (Lutzoni et al 2004). Similarly phylogenies inferred from amino acid sequence data from one or two loci have failed to resolve evolutionary relationships of the Mucorales (Keeling et al 2000, Keeling 2003, Helgason et al 2003), except for a possible sister group relationship with the Mortierellales (Tanabe et al 2004, Tanabe et al 2005) or the Entomophthorales (Keeling 2003). Sequences of the Endogonales however were noticeably absent from all of the amino acid-based phylogenies. Phylogeny reconstructions based on b-tubulin weakly supported a Mucorales + Ento- mophthorales sister group relationship but did not include sequences of the Mortierellales (Keeling 2003).
The genera currently classified within the mono- phyletic Mucorales (Lutzoni et al 2004) have been classified in up to 16 families, based primarily on differences in sexual and asexual reproductive mor- phology (Benny et al 2001). However our study supports the results of another based on three genes that indicated large scale polyphyly at the family level (O’Donnell et al 2001); in that study four of seven F IG
Scanning electron micrographs of Zygomycetes illustrating morphological diversity of sexual and asexual reproductive structures. A–E. Mucorales. Zygospores of A. Cokeromyces recurvatus, B. Cunninghamella homothallicus, C. Radiomyces spectabilis and D. Absidia spinosa. E. Hesseltinella vesiculosa sporangia. F–G. Mortierellales. F. Mortierella (Gamsiella) multidivaricata chlamydospore. G. Lobosporangium transversalis sporangia borne on arachnoid mycelium. H–J. Zoopagales. H. Piptocephalis cormbifera immature sporangia. I. Syncephalis cornu sporophore bearing senescent sporangia with uniseriate sporangiospores. J. Rhopalomyces elegans fertile vesicle with monosporous sporangia. K. Basidiobolus ranarum monosporous sporangium. L. Dimargaritales. Dispira cornuta two-spored sporangia. M–O. Kickxellales. Monosporous sporangia of M. Spiromyces minutus, N. Linderina pennispora and O. Kickxella alabastrina. Bars: A–F, I–O 5 10 mm; G, H 5 20 mm. 876
M YCOLOGIA
families containing two or more genera were inferred to be polyphyletic (i.e. Mucoraceae, Thamnidiaceae, Chaetocladiaceae and Radiomycetaceae). Given that these polyphyletic families comprise more than 80% of the Mucorales, the recent proposal to place all mucoralean families in synonymy with the Muco- raceae, with the exception of the Umbelopsidaceae, seems plausible (Benny 2005). We anticipate that as whole genomes become available these resources will help to accelerate a broad array of basic studies such as elucidating the evolution of sexual reproductive mode and phyloge- netic species recognition (Taylor et al 2000) within these ecologically diverse and economically important fungi. Mortierellales.—This order (F IG . 2F, G) comprises approximately 10% of the known Zygomycota with close to 100 recognized species (Hawksworth et al 1995) distributed among six genera (Benny 2005). With the exception of Mortierella, at more than 90 species, the other genera are monotypic (Aquamor- Aquamortierella, Lobosporangium and Gamsiella) or bitypic (Dissophora and Modicella). Except for Aqua- mortierella and Modicella, which are thought to be saprobic but never have been cultured, all members of this order are characterized by thin, delicate arachnoid-like mycelium (F IG . 2G) and zonate colo- nies that often produce a garlic-like odor in pure culture. Asexual reproduction is by uni- or multi- spored sporangia that either lack a columella or possess a rudimentary one and often by the pro- duction of chlamydospores (F IG . 2F). Sexual repro- duction, where known, is by zygospores which are formed between apposed suspensors (see F IG . 12.9e
in Taylor et al 2004). Although Hesseltine and Ellis (1973) and Benjamin (1979) retained the Mortierellaceae within the Mucorales, the Mortierellales, exclusive of the Umbe- lopsidaceae, was supported strongly as an indepen- dent evolutionary lineage in the combined rDNA phylogeny (F IG . 1). Likewise phylogenies inferred from amino acid and nucleotide sequence data (Gehrig et al 1996, Helgason et al 2003, Lutzoni et al 2004, Tanabe et al 2004) supported a monophyletic Mortierellales; however it has been resolved either as part of a paraphyletic zygomycotan grade (Seif et al 2005) or sister of the Endogonales (Gehrig et al 1996) or Mucorales (Tanabe et al 2004). In addition a preliminary two-locus phylogenetic analysis of complete SSU and partial LSU sequence data (O’Donnell unpubl) suggests that Mortierella might be paraphyletic with respect to Dissophora, Lobospor- angium and Gamsiella (Benny and Blackwell 2004), so generic relationships deserve further study. Expanded taxon sampling is needed before a robust hypothesis of the evolutionary relationships within the Mortier- ellales can be formulated. Taxa formerly recognized as subgenus Micromucor or the Mortierella isabellina-group of Mortierella (Gams 1977) were excluded from Mortierellales and strongly supported (F IG . 1) as monophyletic Umbe- lopsidaceae (Meyer and Gams 2003). This position, as early diverging members of a monophyletic Muco- rales, has been noted elsewhere (F IG . 3; O’Donnell et al 2001, Lutzoni et al 2004). Endogonales.—Symbiotic association of mycorrhizal fungi with plant roots is recognized as economically and ecologically important (Taylor et al 2004, Redecker and Rabb this issue). With the elevation of the Glomales to the Glomeromycota (Schu ¨ ßler et al 2001) the only known member of the Zygomycota sensu stricto that forms such symbioses are the facultatively saprotrophic Endogonales. Formerly treated as a family in the Mucorales (Hesseltine and Ellis 1973), Benjamin (1979) validated Moreau’s (1953) Endogonales by elevating the family to ordinal status. Morton and Benny (1990) subsequently emended the Endogonales to include only the Endogonaceae and Endogone and moved the other genera to a new order, the Glomales (Morton and Benny 1990). The Glomales and Endogonales are distinguished easily in that they produce intracellular, arbuscule-forming endomycorrhizae (AM) and ecto- mycorrhizae, respectively (Morton and Benny 1990, Benny et al 2001). Another hallmark of the Endogo- nales is that some species produce hypogeous fruiting structures called sporocarps that contain zygospores with apposed suspensors (see F IG . 15 in Benny et al 2001). The Endogonales, sometimes called pea-truffles because some species of Endogone produce macro- scopic sporocarps that are pea-like in appearance (Yao et al 1996), now includes four genera (Benny et al 2001, Kirk et al 2001). Phylogenetic studies based on SSU rDNA sequence analysis have indicated a possible sister group relationship with the Mortier- ellales (Gehrig et al 1996). However in the present study the Endogonales and Mucorales formed a strongly supported clade that is sister of the Ascomycota + Basidiomycota + Glomeromycota clade (F IG
nales and Mucorales is supported by morphological evidence because they both form zygospores, in contrast to the Glomeromycota in which zygospores never have been observed (Sanders 1999). Lastly, the novel Endogonales + Mucorales clade has been recovered also from multilocus analyses that included protein coding sequences ( James et al 2006a). W HITE ET AL : P HYLOGENY OF THE Z YGOMYCOTA 877 Yüklə 282,84 Kb. Dostları ilə paylaş:
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