Application of ultrastructural and molecular data in the taxonomy of helotialean fungi
Date
2016-10-11
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Abstract
Tiksikseened (Helotiales sensu auct., Leotiomycetes, Ascomycota) kujutavad endast ˂2 mm läbimõõduga erivärviliste kausjas-peekerjate viljakehadega seeni. Nad on eluviisilt saproobid, parasiidid või sümbiondid (endofüüdid, mükoriisaseened) erinevatel taimedel, aga ka mullas ja vees. Olles küll looduses sagedased organismid, on neid keeruline määrata, sest morfoloogilised kriteeriumid on ebaselged ja molekulaarseks määramiseks napib DNA referentsjärjestusi. Doktoritöö põhieesmärk oli panustada fülogeneesipõhise klassifikatsiooni loomisse selles väheuuritud seenerühmas. Fülogeneesi rekonstrueerimiseks sekveneeriti mitmeid geenilõike. Lisaks uuriti võrdlevalt valitud taksonite morfoloogiat, kaasates transmissioon-elektronmikroskoopia meetodeid. Tulemusena selgus, et monofüleetilised rühmad eristuvad üksteisest mitmete tunnuste kombinatsiooni, mitte üksikute tunnuste poolest, nagu eoskoti tipustruktuur. Viimastele ei peaks andma võtmetähendust, kuivõrd konvergents on selles seenerühmas laialt levinud. Heaks näiteks homoplaasia kohta on jahukirmelise vintske viljakeha välisilme alusel eristatud perekond Encoelia, mis fülogeneesi põhjal osutus polüfüleetiliseks. Kaheksa Encoelia liiki lahknesid fülogeneesipuul kuude sugukonda, kusjuures perekonna tüüpliigiga ei olnud suguluses ükski teine Encoelia liik. Fülogeneesipõhise klassifikatsiooni loomisel taaselustati kaks ajaloolist sugukonda, kirjeldati uusi perekondi ja liike ning avaldati taksonoomilised rekombinatsioonid. Multigeen-fülogeneesipuu klaadid eristusid enamasti ökoloogia poolest. Paljude tiksikseente taksonite kohta saadi olulist ökoloogilist lisateavet, analüüsides koos viljakehade ja keskkonnaproovide ITS rDNA järjestusi. See võimaldas anda nimetuse paljudele avaliku geeniandmebaasi keskkonnasekventside lähteorganismidele. Siinne töö julgustab taksonoome rohkem kasutama DNA triipkoodistamist, soodustamaks koostööd ökoloogidega, kes enamasti tuvastavad seente elutsükli varjatumat poolt – seeneniidistiku etappi.
The helotialean fungi (Helotiales sensu auct., Leotiomycetes Ascomycota) have fruitbodies, which are small (˂2 mm in diameter) varicolored and discoid-cupulate. Their lifestyle is either saprobic, parasitic or symbioitic (endophytic, mycorrhizal) occurring in various plants, but also in water and soil. The general aim of this doctoral thesis was to contribute to creating a phylogeny-based classification of helotialean fungi, a group undersampled with molecular methods. For that purpose, DNA was sequenced, and comparative morphological studies were conducted, including transmission electron microscopy. The ultrastructure of apothecial hairs in the family Lachnaceae varies at the genus level, but the type of ascus apical apparatus of this family was the same except for Lachnellula. Phylogenetic analyses revealed historical characters such as the mealy appearance of apothecia and xero-tolerance to be homoplasious and the genus Encoelia to be polyphyletic with eight studied species distributed among six families. Synapomorphies were distinguished in two resurrected familes: refractive vacuolar bodies in Cenangiaceae and the presence of ionomidotic reaction in Cordieritidaceae. The substratal stromata and anamorph characteristics had also taxonomic significance. Monophyletic groups, distinguished in phylogenetic analyses indicated that helotialean taxa are defined by combination of several characters rather than individual features; reliance on the latter should be avoided. The analyses of ITS rDNA extracted from fruitbodies together with public sequences from various biological samples expanded information on the ecology of studied taxa and allowed identification of many sequenced organisms in public databases at family, genus, or species level. Based on this work taxonomists are encouraged to apply DNA barcoding and to inititate more intense cooperation with ecologists.
The helotialean fungi (Helotiales sensu auct., Leotiomycetes Ascomycota) have fruitbodies, which are small (˂2 mm in diameter) varicolored and discoid-cupulate. Their lifestyle is either saprobic, parasitic or symbioitic (endophytic, mycorrhizal) occurring in various plants, but also in water and soil. The general aim of this doctoral thesis was to contribute to creating a phylogeny-based classification of helotialean fungi, a group undersampled with molecular methods. For that purpose, DNA was sequenced, and comparative morphological studies were conducted, including transmission electron microscopy. The ultrastructure of apothecial hairs in the family Lachnaceae varies at the genus level, but the type of ascus apical apparatus of this family was the same except for Lachnellula. Phylogenetic analyses revealed historical characters such as the mealy appearance of apothecia and xero-tolerance to be homoplasious and the genus Encoelia to be polyphyletic with eight studied species distributed among six families. Synapomorphies were distinguished in two resurrected familes: refractive vacuolar bodies in Cenangiaceae and the presence of ionomidotic reaction in Cordieritidaceae. The substratal stromata and anamorph characteristics had also taxonomic significance. Monophyletic groups, distinguished in phylogenetic analyses indicated that helotialean taxa are defined by combination of several characters rather than individual features; reliance on the latter should be avoided. The analyses of ITS rDNA extracted from fruitbodies together with public sequences from various biological samples expanded information on the ecology of studied taxa and allowed identification of many sequenced organisms in public databases at family, genus, or species level. Based on this work taxonomists are encouraged to apply DNA barcoding and to inititate more intense cooperation with ecologists.
Description
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Keywords
molekulaarbioloogilised uuringud, kottseened, tiksikulaadsed, taksonoomia, molecular biological investigations, Ascomycota, Leotiales, taxonomy