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The Development, Ultrastructural Cytology, and Molecular Phylogeny of the Basal Oomycete Eurychasma dicksonii, Infecting the Filamentous Phaeophyte Algae Ectocarpus siliculosus and Pylaiella littoralis

Lookup NU author(s): Satoshi Sekimoto, Dr Gordon Beakes


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The morphological development, ultrastructural cytology, and molecular phylogeny of Eurychasma dicksonii, a holocarpic oomycete endoparasite of phaeophyte algae, were investigated in laboratory cultures. Infection of the host algae by E. dicksonii is initiated by an adhesorium-like infection apparatus. First non-walled, the parasite cell developed a cell wall and numerous large vacuoles once it had almost completely filled the infected host cell (foamy stage). Large-scale cytoplasmic changes led to the differentiation of a sporangium with peripheral primary cysts. Secondary zoospores appeared to be liberated from the primary cysts in the internal space left after the peripheral spores differentiated. These zoospores contained two phases of peripheral vesicles, most likely homologous to the dorsal encystment vesicles and K-bodies observed in other oomycetes. Following zoospore liberation the walls of the empty cyst were left behind, forming the so-called net sporangium, a distinctive morphological feature of this genus. The morphological and ultrastructural features of Eurychasma were discussed in relation to similarities with other oomycetes. Both SSU rRNA and COII trees pointed to a basal position of Eurychasma among the Oomycetes. The cox2 sequences also revealed that the UGA codon encoded tryptophan, constituting the first report of stop codon reassignment in an oomycete mitochondrion. © 2007 Elsevier GmbH. All rights reserved.

Publication metadata

Author(s): Sekimoto S, Beakes GW, Gachon CMM, Müller DG, Küpper FC, Honda D

Publication type: Article

Publication status: Published

Journal: Protist

Year: 2008

Volume: 159

Issue: 2

Pages: 299-318

ISSN (print): 1434-4610

ISSN (electronic): 1618-0941

Publisher: Urban und Fischer Verlag


DOI: 10.1016/j.protis.2007.11.004

PubMed id: 18243049


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Funder referenceFunder name
MR/K001744/1Medical Research Council