?-1,3-Glucan is one of the main polysaccharide in the cell wall of filamentous fungi, and is known as an aggregation factor of hyphae. The model filamentous fungus Aspergillus nidulans has two ?-1,3-glucan synthases genes, agsA and agsB. We previously reported that AgsB is a primary ?-1,3-glucan synthase in vegetative hyphae, but the function of AgsA remains unclear. Here we constructed strains overexpressing agsA (agsAOE) or agsB (agsBOE) for clarifying the role of ?-1,3-glucan in hyphal aggregation. In liquid culture, the hyphae of the wild-type and agsBOE strain formed tightly aggregated pellet, whereas the agsAOE aggregated loosely. To reveal these phenotypic difference between the overexpression strains, we analyzed the chemical structure of ?-1,3-glucan from both strains. Interestingly peak molecular mass of ?-1,3-glucan from the agsAOE strain (1,480 ± 80 kDa) was four times than that from agsBOE strains (372 ± 47 kDa). We also analyzed localization of ?-1,3-glucan in the cell wall by fluorescent labelling of ?-1,3-glucan with ?-1,3-glucan-binding domain-fused GFP (AGBD-GFP). ?-1,3-Glucan of the agsBOE cells was clearly labelled with AGBD-GFP, whereas only weakly labelled in the agsAOE cells. In addition, ?-1,3-glucanase treated agsAOE cells were clearly labelled with AGBD-GFP. These results suggest that ?-1,3-glucan was localized outermost layer in the agsBOE strain, whereas ?- 1,3-glucan covered most of ?-1,3-glucan in the agsAOE strain. Together the degree of hyphal aggregation seemed to be controlled not only by the amount of ?-1,3-glucan but also by the molecular mass and localization of ?-1,3-glucan in the cell wall. The different distribution of ?-1,3-glucan in the cell wall of the agsAOE and agsBOE strains may be caused by the difference in the physicochemical properties of ?-1,3-glucans synthesized by AgsA and AgsB. In general, polysaccharides of which molecular mass is lager are usually less soluble than the smaller one. Therefore, the ?-1,3-glucan having larger molecular mass might be localized in the inner layer, whereas smaller one in the outer layer of the cell wall. Here, we discuss the relationship between molecular mass and distribution of ?-1,3-glucan in the cell wall.
Full conference title:
- Fungal Genetics Conference 30th (2019)