Devonian Fungi: Interactions with the Green Alga Palaeonitella

This paper describes three new taxa of fossil aquatic fungi preserved in 400-million-year-old Lower Devonian Rhynie Chert. All of the fungal morphotypes are attached to cells of the green alga Palaeonitella cranii. Milleromyces rhyniensis is characterized by a holocarpic, epibiotic ^oosporangium with an elongate discharge tube that penetrates the host cell wall; arising from the base of the sporangium is an extensive rhizoidal system. Stages in infection by presumed zoospores are documented. In Lyonomyces pyriformis the globose-pyriform thallus is embedded in the surface coating of the cell wall. At the base of each thallus is a single rhizoid. Krispiromyces is extramatrical, holocarpic, and characterized by a short beak-like discharge papilla. The rhizoidal system appears to be apophysate. Some of these fungi were probably saprobes, while others were deemed parasitic because of the extensive hypertrophy of some of the algal cells. Although not all life history stages are represented, the discovery of these Lower Devonian forms greatly expands our knowledge of the biology and diversity of aquatic fungi in an ancient freshwater ecosystem

Fossil arbuscular mycorrhizae from the Early Devonian

The 400 million-year-old Rhynie chert has provided a wealth of information not only of early land plants, but also of the fungi that inhabited this paleoecosystem. In this paper we report the first unequivocal evidence of arbuscules in an endomycorrhizal symbiosis. A new genus, Glomites, is characterized by extraradical, aseptate hyphae with a two-parted wall, and an intraradical, highly branched network of thin-walled hyphae. Hyphal branches produce terminal, elongate-globose multilayered spores that lack a basal septum. Other hyphae penetrate cell walls and form arbuscules. Arbuscules are morphologically identical to those of living arbuscular mycorrhizae (AM) in consisting of a basal trunk and highly dichotomous distal branches that form a bush-like tuft. Arbuscules are confined to a narrow band of specialized thinwalled cells in the outer cortex that continue to be meristematic. Features of the fossil biotroph are compared with those of extant arbuscular mycorrhizae. Although interpretations regarding the evolution of mycorrhizal mutualisms continue to be speculative, the demonstration of arbuscules in the Early Devonian indicates that nutrient transfer is an ancient phenomenon that may have been in existence when plants invaded the land

Abstracts from the 20th International Symposium on Signal Transduction at the Blood-Brain Barriers

https://deepblue.lib.umich.edu/bitstream/2027.42/138963/1/12987_2017_Article_71.pd

A crescent-shaped ALIX dimer targets ESCRT-III CHMP4 filaments

International audienceALIX recruits ESCRT-III CHMP4 and is involved in membrane remodeling during endosomal receptor sorting, budding of some enveloped viruses, and cytokinesis. We show that ALIX dimerizes via the middle domain (ALIX(-V)) in solution. Structural modeling based on small angle X-ray scattering (SAXS) data reveals an elongated crescent-shaped conformation for dimeric ALIX lacking the proline-rich domain (ALIX(BRO1-V)). Mutations at the dimerization interface prevent dimerization and induce an open elongated monomeric conformation of ALIX(-V) as determined by SAXS modeling. ALIX dimerizes in vivo and dimeric ALIX colocalizes with CHMP4B upon coexpression. We show further that ALIX dimerization affects HIV-1 budding. C-terminally truncated activated CHMP4B retaining the ALIX binding site forms linear, circular, and helical filaments in vitro, which can be bridged by ALIX. Our data suggest that dimeric ALIX represents the active form that interacts with ESCRT-III CHMP4 polymers and functions as a scaffolding protein during membrane remodeling processes