Intercellular communication through the septal pore in Aspergillus oryzae

A network of interconnected hyphae is usually formed in mycelia colonies of filamentous ascomycete fungi. Cytoplasmic continuity via septal pores and hyphal fusion facilitate translocation of nutrients within colonies. In Aspergillus species, molecular mechanism regulation such mycelial network has not been intensively studied. Recently, it has been reported that 2 homologous proteins, so (Neurospora crassa) and Pro40 (Sordaria macrospora) localize at the septal pore, similarly to Woronin bodies which plug during hyphal injury. These proteins are known to be necessary for hyphal fusion and sexual development in the ascomycete fungi. This study presents the effects in response to different physical and chemical stresses like high pH, low pH,and depletion of carbon and nitrogen sources exhibited by A. oryzae strains ITDI 3002 and ITDI 3038, seen as changes in their cytoplasmic streaming and formation of anastomoses among hyphae. Effects of the following stress were correlated with the ability of the organism to secrete enzymes, particularly, alpha-amylase. Application of the different stress resulted to the arrest of cytoplasmic streaming and fusion of hyphae in both strains, ITDI 3002 and ITDI 3038. In Ao 3038, it was observed that there was a decrease in alpha-amylase activity when subjected to high pH and low pH while increase in the enzyme activity was observed when carbon and nitrogen sources were added. However, statistical analysis support that stresses applied on the strains may not have been enough to elicit significant variation between the treatments and control. Microscopic investigations of AoSO-EGFP fusion protein showed localization of AoSO in the septal pore as a punctuate dot under various stress conditions (high/low temperature, extreme acidic/alkaline pH, nitrogen/carbon starvation). This suggests that AoSO may regulate intercellular communication during environmental changes. In the Aohex 1 deletion strain lacking woronin bodies, accumulation of the protein on the central portion of the septum was still evident under these stress conditions, although its migration to the septal pore was delayed. For visualizing cell to cell communication through cytoplasmic streaming between hyphal compartments, the Dendra 2 system was used in A.oryzae. For the control strain, cell to cell movement of Dendra 2 was obstructed under both stressed conditions. It appears that migration of Dendra 2 to the neighboring compartment was blocked. On the other hand, delta AoSO strain showed converted light red flurescence of Dendra 2 (purple color) to the neighboring compartment under low temperature. This might suggest that AoSO participates in controlling cytoplasm communication between hyphal compartments.