Characterization of a bZIP Transcription Factor ZipD in Aspergillus flavus 

Aspergillus flavus produces aflatoxin B1, a Group 1 carcinogen, that causes severe economic and agricultural losses and invasive aspergillosis in humans. During its growth, A. flavusdevelops threadlike structures called hyphae, which form a continuous mycelium that associated with host colonization and toxin production. Transcription factors are considered as regulator of development and pathogenicity and major transcription factor families include Zinc Finger (C2H2), basic helix-loop-helix (bHLH), and basic leucine zipper (bZIP).Among these families, bZIP proteins have been shown to be associated with growth, metabolism, and stress tolerance. In A. fumigatus, the bZIP Transcription factor zipD is known to regulate signalling pathways and cell wall integrity. However,the ortholog of zipD in A. flavus has not been characterized. To investigate this, we generated a deletion mutant and a complemented strain of zipD in A. flavus. First, zipD deletion mutant showed reduced colony growth and conidia production. Second, ∆zipD strain exhibited increased sclerotia formation, suggesting a role in sexual development. Finally, ∆zipD strain displayed reduced conidial colonization in pathogenicity assays using corn, bean, and meju compared to the wild type. All of these phenotypes were recovered in the complemented strain. These results suggest that zipD functions as a regulator of both growth developmental processes and pathogenic traits in A. flavus.