Studies On Phylogenetic Relationships Among Representative Groups Of Four Orders In Myxomycetes Based On Living Habit, Morphogenesis And Molecular Characteristics

Myxomycetes are a kind of eukaryotic organisms that exist widely in terrestrial ecosystem. Their specific morphological characteristics of vegetative and fruiting body are shaped by long-term evolution and selection between their habitat and themself. The classification of Myxomycetes depends mainly on morphological characteristics of fruiting body and includes six main groups (Ceratiomyxales, Echinosteliales, Liceales, Trichiales, Physarales and Stemonitales). Ceratiomyxales, a group of species with exospores, are distinctly different from the other five orders, a group of species with endospores. The phylogenetic relationships of five orders with endospores have been attracting the attention of many researchers, but there are too many different contentions based on different morphological and molecular characteristics. In the paper, based on their living habits in nature, features of morphogenesis, and conservative and variational molecular characteristics, the positions of Liceales, Trichiales, Physarales and Stemonitales in the phylogeny evolution of Myxomycetes were studied. Hope to provide some new theoretical proofs for the development of taxonomy and evolutionary biology of Myxomycetes. Main results for this study are as follows:1.78species, which were collected from some typical regions of Jilin Province, Sichuan Province and Tibet Autonomous Region, belonged to Ceratiomyxales, Liceales, Trichiales, Physarales and Stemonitales,7families,22genus. Their substratum types were litter, log and bark, whose pH was no significant difference except that of the litter. It was easily affected by species of tree. Each taxonomic category had preferential substratum type and pH. The substratum types of Ceratiomyxales and Liceales were stable and log, and those of Trichiales, Physarales and Stemonitales were diverse. Those of Trichiales were mainly log, those of Stemonitales were log and litter, and those of Physarales were mainly litter. In addition, there was no significant difference of pH among five groups; Diversity of internal bacterium of14samples in four orders was detected by16S rDNA gene. Bacteria were only detected from9samples and belonged to Proteobacteria (including Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria) and Actinobacteria. Gammaproteobacteria was the dominant population. In addition, there may be some difference of bacterium diversity in different habitats and pH range, not affected by taxonomic status and needed more data to prove that; The foraging process of six phaneroplasmodia (Didymium megalosporum, D. squamulosum, Physarum melleum, Badhamia gracilis, Fuligo septica and Physarella oblonga) to three treatments during 48hours was characteristic for themselves. The nutritional status of each phaneroplasmodium was related to its habitat and the nutritional requirement of each phneroplasmodium was related to its taxonomic status.2. Based on relevant literature and14species’features of morphogenesis in Trichiales, Physarales and Stemonitales, the forming process and growth method of plasmodia among Trichiales, Physarales and Stemonitales were similar. There were also many similarities in the morphological characteristics between Physarales and Stemonitales during the forming process of fruiting body. But Stemonitales had an advanced and mobile coralloidal mass. Based on reported morphogenesis features of Liceales, from the perspective of complexity of plasmodial life history strategy and fruiting body morphology, Liceales was more primitive group, and Trichiales, Physarales and Stemonitales were more advanced groups. In addition, there was a homology among Trichiales, Physarales and Stemonitale, and Physarales and Stemonitale may derive from Trichiales.3. Partial cytochrome oxidase I genes of Ceratiomyxa fruticulosa, D. megalosporum, D. squamulosum, Diderma radiatum, Hemitrichia serpula and Trichia decipiens were first gained. That of Ceratiomyxales was longer than those of Echinosteliales, Trichiales, Physarales and Stemonitales, which were highly conservative and no intron area. When the DNA was transcribed into mRNA, those of Physarales and Stemonitales had more insertion of Cs, but those of Echinosteliales and Trichiales had not. The phylogenetic tree constructed by maximum likelihood method gathered Physarales and Stemonitales together, which were more advanced groups; Partial DNA sequence of a-tubulin of plasmodia in D. megalosporum was1159bp in length, whose region from177bp to235bp was intron area and remaining regions were exon area. The coded amino acid sequence was366aa in length and was fully identical with the same sequence of P. polycephalum. But the DNA sequences between them were different, and there were same sense mutation; Eighteen genes of ITS region and5.8S rDNA of ribosome were gained firstly from15species, including Craterium leucocephalum, P. compressum (fruiting body and plasmodium), P. gyrosum, P. pusillum, P. oblonga (fruiting body and plasmodium), B. gracilis, B. utricularis, F. septica, L. fragilis (Sichuan Province and Inner Mongolia Autonomous Region), D. megalosporum, D. squamulosum, D. chondrioderma, Arcyria occidentalis, Enteridium splendens, Cribraria argiliacea. Those of12species in Physarales were800-2000bp in length and had a large variation especially at the region of ITS1. Those of species in Liceales and Trichiales were less than in Physarales in the length and the value of GC%. So the speed of evolution of Physarales was faster than those of Trichiales and Liceales.Therefore, based on living habits in nature, morphogenesis and molecular characteristics of Liceales, Trichiales, Physarales and Stemonitales, Liceales were more primitive groups, and Trichiales, Physarales and Stemonitales were more advanced groups. In addition, Physarales and Stemonitale had close gentic relationship and were derived from Trichiales.