ASPERGILLUS-FUMIGATUS ARP1 MODULATES CONIDIAL PIGMENTATION AND COMPLEMENT DEPOSITION

Aspergillus fumigatus is an important pathogen causing invasive pulmon ary aspergillosis in immunocompromised patients. The fungus propagates by conidia, which are the infectious structures inhaled by the human host. Opsonophagocytosis is thought to contribute to clearance of the inhaled conidia, a process that is facilitated by complement depositio n on conidial surfaces. We now show that conidial colour mutants exhib it significant increases in C3 binding capacity compared with wild typ e. A reddish-pink mutation that led to enhanced C3 binding was complem ented by a cosmid clone. A 3.3 kb DNA fragment from the subsequently r escued cosmid was sufficient to restore the bluish-green conidial pigm ent. The bluish-green transformant exhibited a level of C3 binding sim ilar to that of the parental strain. A gene, designated arp1, was resp onsible for the complementation. Comparison of the genomic and cDNA se quences of arp1 revealed that it has two introns and encodes a putativ e protein of 168 amino acids. Arp1 is very similar to scytalone dehydr atase, an enzyme involved in 1,8-dihydroxynaphthalene-melanin synthesi s in Colletotrichum lagenarium and Magnaporthe grisea. Northern hybrid ization analysis revealed that arp1 is developmentally regulated, bein g expressed during conidiation. Disruption of arp1 resulted in reddish -pink conidia and increased C3 binding. Our studies suggest that arp1 modulates the bluish-green pigmentation of conidia as well as compleme nt deposition.