The increase in cell volume and nuclear number of the koji-fungus Aspergillus oryzae contributes to its high enzyme productivity

Abstract The regulation of cell volume and nuclear number in multi-nucleate organisms remains largely unknown. The koji-fungus Aspergillus oryzae has been used in traditional Japanese brewing and fermentation. We discovered that cell volume of hyphae increases tenfold, and the number of nuclei in the hyphal cells also increases tenfold, exceeding 200. The increase in cell volume and nuclear number is unique to A. oryzae and correlates with its high enzyme production capabilities. Through transcriptome analysis of thick hyphae isolated via laser microdissection and SNP analysis of practical strains from koji manufacturers, we identified a calcium channel and glycosyl transferase involved in cell volume expansion. Additionally, we indicated that specific amino acids and activation of the TOR pathway are essential for increasing nuclear number. This study not only deepens our understanding of the evolutionary processes that promote high enzyme productivity through fungal breeding, but also provides valuable insights into the molecular mechanisms regulating cell volume and nuclear number in multi-nucleate organisms.