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Title: BIOSYNTHESIS OF THE PENTAKETIDE, 1,3,6,8-T4HN IN ASPERGILLUS FUMIGATUS REQUIRES BOTH POLYKETIDE SYNTHASE AND AYG1P

Author
item TSAI, HUEI-FUNG
item FUJII, ISAO
item WATANABE, AKIRA
item Wheeler, Michael - Mike
item CHANG, YUN
item EBIZUKA, YUTAKA
item KWON-CHUNG, K.

Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/21/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Polyketide synthase (Alb1p encoded by alb1), THN reductase (encoded by arp2) and scytalone dehydratase (encoded by arp1) have been reported to catalyze the first three steps of the pentaketide melanin pathway. In the human pathogenic fungus Aspergillus fumigatus, the ayg1 (aspergillus yellowish-green 1) gene is one of the six clustered genes involved in conidial pigmentation. However, its function remains unknown since no homolog has yet to be found in the database. We show that the ayg1 deletant is insensitive to trycyclazole and neither flaviolin nor 1,3,6,8- tetrahydroxynaphthalen (T4HN) were detected in its culture extract. A double disruption of alb1 and ayg1 resulted in an albino conidial phenotype indicating that alb1 functions upstream of ayg1. Conversely, both the arp1+ayg1 and arp2+ayg1 double deletions resulted in a conidial color similar to that of the ayg1 deletant. These results suggested that ayg1 functions upstream of the arp1 and arp2 genes and is essential for T4HN production. These findings are different from the case in Collectrotrichum lagenarium where PKS (polyketides synthase) alone is enough to synthesize T4HN (pentaketide) by the heterologous expression system using Aspergillus oryzae as a host. Interestingly, overexpression of alb1 in A. oryzae led to production of the heptaketide, naphthopyrone, rather than the pentaketide, T4HN. We hypothesize ayg1 is required in A. fumigatus to synthesize the pentaketide initiated with alb1. In order to test this hypothesis, ayg1 was introduced into A. oryzae with or without alb1. Production of T4HN occurred in A. oryzae only when both alb1 and ayg1 were overexpressed. This demonstrated that Ayg1p (encoded by ayg1) is essential for Alb1p to synthesize T4HN in A. fumigatus and A. oryzae.