Dee Jaclyn M, Mollicone Marilyn, Longcore Joyce E, Roberson Robert W, Berbee Mary L
Department of Botany, University of British Columbia, Vancouver, British Columbia, V6T-1Z4 Canada
School of Biology and Ecology, University of Maine, Orono, Maine 04469.
Mycologia. 2015 Jul-Aug;107(4):710-28. doi: 10.3852/14-275. Epub 2015 Apr 24.
The evolution of filamentous hyphae underlies an astounding diversity of fungal form and function. We studied the cellular structure and evolutionary origins of the filamentous form in the Monoblepharidomycetes (Chytridiomycota), an early-diverging fungal lineage that displays an exceptional range of body types, from crescent-shaped single cells to sprawling hyphae. To do so, we combined light and transmission electron microscopic analyses of hyphal cytoplasm with molecular phylogenetic reconstructions. Hyphae of Monoblepharidomycetes lack a complex aggregation of secretory vesicles at the hyphal apex (i.e. Spitzenkörper), have centrosomes as primary microtubule organizing centers and have stacked Golgi cisternae instead of tubular/fenestrated Golgi equivalents. The cytoplasmic distribution of actin in Monoblepharidomycetes is comparable to the arrangement observed previously in other filamentous fungi. To discern the origins of Monoblepharidomycetes hyphae, we inferred a phylogeny of the fungi based on 18S and 28S ribosomal DNA sequence data with maximum likelihood and Bayesian inference methods. We focused sampling on Monoblepharidomycetes to infer intergeneric relationships within the class and determined 78 new sequences. Analyses showed class Monoblepharidomycetes to be monophyletic and nested within Chytridiomycota. Hyphal Monoblepharidomycetes formed a clade sister to the genera without hyphae, Harpochytrium and Oedogoniomyces. A likelihood ancestral state reconstruction indicated that hyphae arose independently within the Monoblepharidomycetes lineage and in at least two other lineages. Cytological differences among monoblepharidalean and other fungal hyphae are consistent with these convergent origins.
丝状菌丝的演化是真菌形态和功能惊人多样性的基础。我们研究了单毛菌纲（壶菌门）中丝状形态的细胞结构和进化起源，单毛菌纲是一个早期分化的真菌谱系，展现出从月牙形单细胞到蔓延菌丝的一系列特殊身体类型。为此，我们将菌丝细胞质的光学显微镜和透射电子显微镜分析与分子系统发育重建相结合。单毛菌纲的菌丝在菌丝顶端缺乏分泌囊泡的复杂聚集（即，Spitzenkörper），以中心体作为主要微管组织中心，并且具有堆叠的高尔基体潴泡而不是管状/有孔的高尔基体等价物。单毛菌纲中肌动蛋白的细胞质分布与先前在其他丝状真菌中观察到的排列方式相当。为了弄清单毛菌纲菌丝的起源，我们基于18S和28S核糖体DNA序列数据，采用最大似然法和贝叶斯推断法推断了真菌的系统发育。我们集中对单毛菌纲进行采样以推断该纲内属间关系，并确定了78个新序列。分析表明单毛菌纲是单系的，并嵌套在壶菌门内。有菌丝的单毛菌纲形成了一个分支，是无菌丝的属——哈氏壶菌属和鞘藻壶菌属的姐妹分支。似然祖先状态重建表明，菌丝在单毛菌纲谱系内以及至少其他两个谱系中独立出现。单毛菌目真菌和其他真菌菌丝之间的细胞学差异与这些趋同起源是一致的。
