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Eukaryotic Cell, August 2006, p. 1328-1336, Vol. 5, No. 8
1535-9778/06/$08.00+0     doi:10.1128/EC.00024-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Functional Analysis of the ATG8 Homologue Aoatg8 and Role of Autophagy in Differentiation and Germination in Aspergillus oryzae

Takashi Kikuma, Mamoru Ohneda,{dagger} Manabu Arioka, and Katsuhiko Kitamoto*

Department of Biotechnology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan

Received 30 January 2006/ Accepted 2 June 2006

Autophagy is a well-known degradation system, induced by nutrient starvation, in which cytoplasmic components and organelles are digested via vacuoles/lysosomes. Recently, it was reported that autophagy is involved in the turnover of cellular components, development, differentiation, immune responses, protection against pathogens, and cell death. In this study, we isolated the ATG8 gene homologue Aoatg8 from the filamentous fungus Aspergillus oryzae and visualized autophagy by the expression of DsRed2-AoAtg8 and enhanced green fluorescent protein-AoAtg8 fusion proteins in this fungus. While the fusion proteins were localized in dot structures which are preautophagosomal structure-like structures under normal growth conditions, starvation or rapamycin treatment caused their accumulation in vacuoles. DsRed2 expressed in the cytoplasm was also taken up into vacuoles under starvation conditions or during the differentiation of conidiophores and conidial germination. Deletion mutants of Aoatg8 did not form aerial hyphae and conidia, and DsRed2 was not localized in vacuoles under starvation conditions, indicating that Aoatg8 is essential for autophagy. Furthermore, Aoatg8 conditional mutants showed delayed conidial germination in the absence of nitrogen sources. These results suggest that autophagy functions in both the differentiation of aerial hyphae and in conidial germination in A. oryzae.

* Corresponding author. Mailing address: Department of Biotechnology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan. Phone: 81-3-5841-5161. Fax: 81-3-5841-8033. E-mail: akitamo{at}mail.ecc.u-tokyo.ac.jp.

{dagger} Present address: Department of Cell Biology, National Institute for Basic Biology, Okazaki 444-5858, Japan.

Eukaryotic Cell, August 2006, p. 1328-1336, Vol. 5, No. 8
1535-9778/06/$08.00+0     doi:10.1128/EC.00024-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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