Hyphal heterogeneity in Aspergillus oryzae is the result of dynamic closure of septa by Woronin bodies

Hyphae of higher fungi are compartmentalized by septa. These septa contain a central pore that allows for inter-compartmental and inter-hyphal cytoplasmic streaming. The cytoplasm within the mycelium is therefore considered to be a continuous system. In this study, however, we demonstrate by laser dissection that 40% of the apical septa of exploring hyphae of Aspergillus oryzae are closed. Closure of septa correlated with the presence of a peroxisome-derived organelle, known as Woronin body, near the septal pore. The location of Woronin bodies in the hyphae was dynamic and, as a result, plugging of the septal pore was reversible. Septal plugging was abolished in a ?Aohex1 strain that cannot form Woronin bodies. Notably, hyphal heterogeneity was also affected in the ?Aohex1 strain. Wild-type strains of A.?oryzae showed heterogeneous distribution of GFP between neighbouring hyphae at the outer part of the colony when the reporter was expressed from the promoter of the glucoamylase gene glaA or the a-glucuronidase gene aguA. In contrast, GFP fluorescence showed a normal distribution in the case of the ?Aohex1 strain. Taken together, it is concluded that Woronin bodies maintain hyphal heterogeneity in a fungal mycelium by impeding cytoplasmic continuity.