Localisation and substrate specificities of transglycanases in charophyte algae relate to development and morphology

Abstract

Cell wall-modifying enzymes were previously investigated in charophyte green algae (CGA) from cultures of uniform age, giving limited insight into their roles. Therefore, we investigated the in situ localisation and specificity of enzymes acting on hemicelluloses in CGA genera of different morphologies and developmental stages. In vivo transglycosylation between xyloglucan and an endogenous donor in filamentous Klebsormidium and Zygnema showed action in longitudinal cell walls of young (1 month) but not old cells (1 year), suggesting involvement in cell growth. Contrastingly, in parenchymatous Chara, transglycanase action occurred in all cell planes. In Klebsormidium and Zygnema, enzyme action predominately co-localised with xyloglucans and mannans, to a lesser extent mixed-linkage β-glucan (MLG), indicating predominantly xyloglucan:xyloglucan endotransglucosylase (XET). Novel transglycosylation activities between xyloglucan and xylan, and xyloglucan and galactomannan were identified in vitro, in both genera. Our results show that several cell wall-modifying enzymes are present in CGA and that differences in morphology and cell age are related to enzyme localisation and specificity. This indicates an evolutionary significance of cell wall modifications, as similar changes are known from their immediate descendants, the land plants.