Cell wall characteristics during sexual reproduction of Mougeotia sp. (Zygnematophyceae) revealed by electron microscopy, glycan microarrays and RAMAN spectroscopy

Abstract

Mougeotia spp. collected from field samples were investigated for their conjugation morphology by light-, fluorescence-, scanning- and transmission electron microscopy. During a scalarifom conjugation, the extragametangial zygospores were initially surrounded by a thin cell wall that developed into a multi-layered zygospore wall. Maturing zygospores turned dark brown and were filled with storage compounds such as lipids and starch. While M. parvula had a smooth surface, M. disjuncta had a punctated surface structure and a prominent suture. The zygospore wall consisted of a polysaccharide rich endospore, followed by a thin layer with a lipid-like appaerance, a massive electron dense mesospore and a very thin exospore composed of polysaccharides. Glycan microarray analysis of zygospores of different developmental stages revealed the occurrence of pectins and hemicelluloses, mostly composed of homogalacturonan (HG), xyloglucans, xylans, arabino-galactan proteins and extensins. In situ localization by the probe OG7-13AF 488 labelled HG in young zygospore walls, vegetative filaments and most prominently in conjugation tubes and cross walls. Raman imaging showed the distribution of proteins, lipids, carbohydrates and aromatic components of the mature zygospore with a spatial resolution of ~ 250 nm. The carbohydrate nature of the endo- and exospore was confirmed and in-between an enrichment of lipids and aromatic components, probably algaenan or a sporopollenin-like material. Taken together, these results indicate that during zygospore formation, reorganizations of the cell walls occured, leading to a resistant and protective structure.

Search for evolutionary roots of land plant arabinogalactan‐proteins in charophytes: presence of a rhamnogalactan‐protein in Spirogyra pratensis (Zygnematophyceae)

“…and S. mirabilis . The strongest interaction in both cases was also detected with JIM13 ( Permann et al, 2021a , b ). Because AGP-RG I-complexes have been described for Arabidopsis ( Tan et al, 2013 ), we also tested two antibodies specific for RG I (namely INRA-RU1 and -2).…”

“…Xyloglucan was originally assumed to be absent in CGA ( Popper and Fry, 2003 ), but there is now evidence that xyloglucans evolved in these algae ( Mikkelsen et al, 2021 ) and act as a substrate of unusual charophytic transglycosylases ( Franková and Fry, 2021 ). Evidence for xylans and xyloglucans in CGA is further based on glycan microarrays with antibodies directed against epitopes present in these polysaccharides ( Domozych et al, 2009 ; Eder and Lütz-Meindl, 2008 ; Ikegaya et al, 2012 ; Mikkelsen et al, 2021 ; Permann et al, 2021b ; Sørensen et al, 2011 ), as well as structure elucidation ( Ikegaya et al, 2008 ; Mikkelsen et al, 2021 ). These analytical data are complemented by studies of biosynthetic enzymes ( Del-Bem and Vincentz, 2010 ; Mikkelsen et al, 2014 , 2021 ; Nishiyama et al, 2018 ).…”

Comparative transcriptomics reveals the molecular toolkit used by an algivorous protist for cell wall perforation

“…The conjugating green alga Mougeotia sp. possesses a cell wall with certain similarities to those of the closely related land plants, including structural components such as crystalline cellulose microfibrils and gel-like pectins 6,7 . We suspected that Orciraptor utilises carbohydrate-active enzymes (CAZymes) to degrade these polymers (e.g.…”

Cryogenian glacial habitats as a plant terrestrialisation cradle – the origin of the anydrophytes and Zygnematophyceae split

“…As shown by streptophyte algal genus Spirotaenia, which has been shown to be a member of the Mesostigmatophyceae (Gontcharov and Melkonian 2004;Wickett et al, 2014) conjugation in streptophyte green algae is a homoplasious feature; the result of independent convergent evolution (Cheng et al, 2019 ) -in both cases potentially linked to glaciation conditions. Stress-resistant zygospores of Zygnematophyceae are covered by surface cell wall sporopolenin-like material (Permann et al, 2021) so we looked into known Cryogenian acritarchs and, despite an overall reduction in acritarchs diversity during the Cryogenian (Huntley et al, 2006), few new types of acritarchs appeared which seem possible to be potentially interpreted as Zygnematophyceae zygospores (Moczydlowska 2008) even on the ultrastructural level (Moczydlowska et al, 2010). This possibility will certainly require the attention of specialists in the future (see also Discussion -Moczydlowska and Liu 2020).…”