Aspergillus flavus GPI-anchored protein-encoding ecm33 has a role in growth, development, aflatoxin biosynthesis, and maize infection

Authors: Chang, Perng Kuang; ZHANG, QI - Oil Crops Research Institute - China; Scharfenstein, Leslie; Mack, Brian; YOSHIMI, AKIRA - Tohoku University; MIYAZAWA, KEN - Tohoku University; ABE, KEIETSU - Tohoku University

Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2018
Publication Date: 4/25/2018
Citation: Chang, P.-K., Zhang, Q., Scharfenstein, L.L., Mack, B.M., Yoshimi, A., Miyazawa, K., Abe, K. 2018. Aspergillus flavus GPI-anchored protein-encoding ecm33 has a role in growth, development, aflatoxin biosynthesis, and maize infection. Applied Microbiology and Biotechnology. 102:5209-5220. https://doi.org/10.1007/s00253-018-9012-7.
DOI: https://doi.org/10.1007/s00253-018-9012-7

Interpretive Summary: Aspergillus flavus, a saprophytic fungus, usually lives on decaying vegetation. When encountering nutrient-rich crops, the opportunistic pathogen transiently turns parasitic, killing and macerating host tissues. Plant innate immunity relies primarily on the detection of invading pathogens. Cell wall components such as chitin and ß-glucan are elicitors involved in microbe-associated molecular patterns recognized by host plants. Few genes involved in cell wall integrity of A. flavus have been studied. In this work, we examined the function of a gene that encodes a cell wall organization protein. We found that a defect in this gene slowed colony growth, decreased conidiation and altered conidial color but it elevated sclerotial production and increased the sensitivity to a cell wall perturbing agent. Analyses of cell wall of the gene mutant strain showed that its a-glucan was decreased but its chitin and ß-glucan were increased. Compromised cell wall integrity appeared to also affect A. flavus growth and development.

Technical Abstract: Many glycosylphosphatidylinositol-anchored proteins (GPI-APs) of fungi are membrane enzymes, organization components, and extracellular matrix adhesins. We analyzed eight Aspergillus flavus transcriptomes for the GPI-AP gene family and identified AFLA_040110, AFLA_063860 and AFLA_113120 to be among the top two highly expressed genes. Disruption of the former two genes did not drastically affect A. flavus growth and development. In contrast, disruption of AFLA_113120, an orthologue of Saccharomyces cerevisiae ECM33, decreased vegetative growth and conidiation, promoted sclerotial production and altered conidial pigmentation. The developmental defects were remediated by incubation under constant light. The A. flavus ecm33 null mutant showed decreased sensitivity to congo red at low concentrations (25-50 µg/mL) but had increased sensitivity to calcofluor white at high concentrations (250-500 µg/mL). Analyses of cell wall carbohydrates indicated that the a-glucan content was decreased but the contents of chitin and ß-glucan were increased in the mutant strain. We concluded that A. flavus Ecm33 is critical for proper cell wall composition that plays an important role in cell wall integrity.