Callose deposition is essential for the completion of cytokinesis in the unicellular alga,Penium margaritaceum

Abstract

Cytokinesis in land plants involves the formation of a cell plate that develops into the new cell wall. Callose is a β-1,3 glucan that transiently accumulates at later stages of cell plate development and is thought to stabilize the delicate membrane network of the cell plate as it expands. Cytokinetic callose deposition is currently considered specific to multicellular plant species as it has not been detected in unicellular algae. Here we present callose at the cytokinesis junction of the unicellular charophyte, Penium margaritaceum. Notably, callose deposition at the division plane of P. margaritaceum showed distinct, spatiotemporal patterns that could represent distinct roles of this polymer in cytokinesis and cell wall assembly. Pharmacological inhibition of cytokinetic callose deposition by Endosidin 7 treatment resulted in cytokinesis defects, consistent with the essential role for this polymer in P. margaritaceum cell division. Cell wall deposition and assembly at the isthmus zone was also affected by the absence of callose, demonstrating the dynamic nature of new wall assembly in P. margaritaceum. The identification of candidate callose synthase genes provides molecular evidence for callose biosynthesis in P. margaritaceum. The evolutionary implications of cytokinetic callose in this unicellular Zygnematopycean alga is discussed in the context of the conquest of land by plants. Summary Statement Evolutionarily conserved callose in Penium margaritaceum is essential for the completion of cytokinesis.

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

“…Mixed-linked glucans known from grasses (Gibeaut and Carpita, 1993) and also from Equisetum (Fry et al, 2008) have also been detected in different CGA, although they were mainly present in the alkalisoluble fractions Sørensen et al, 2011). Callose was not found in cell walls of Micrasterias but was present in Zygnema (Herburger and Holzinger, 2015) and it is essential for the completion of cytokinesis in Penium (Davis et al, 2020).…”

Plant cytokinesis and the construction of new cell wall

“…Notably, ES7 does not inhibit wound or stress‐induced callose. The cytokinetic defects resulting from ES7 application both in higher plants and algae support the evolutionarily conserved role of the polymer in cytokinesis [77,78]. The failure of cell plate maturation with ES7 application indicates that callose is likely a contributor to the stabilizing or spreading force as predicted by modelling [76] (Fig.…”

“…Chemical biology using ES7 and SMIFH2 informed the role of callose and formins, respectively, in cytokinesis [77,78,108] and can be instrumental in dissecting different aspects of cytokinesis at a spatiotemporal level while overcoming lethality.…”

“…Established cell culture systems, such as BY-2 cultures [123] or algae [78], are amenable to synchronization and can be used to establish quick pipelines for interrogation. Conditional mutants, such as the temperature sensitive tplate mutant, can overcome many of the challenges with canonical cytokinesis mutants [124].…”

Subcellular positioning during cell division and cell plate formation in maize

“…Several RAB-GTPases and KNOLLE localize to the cell plate and motile particles. We incubated maize leaves with Endosidin 7 (ES7), a chemical that inhibits cytokinesisspecific callose deposition in Arabidopsis (Park et al, 2014) and disrupts cytokinesis in algae (Davis et al, 2020). ES7 pulse treatments did not affect accumulation of cell plate localized proteins or disrupt cell plate morphology in maize.…”