Hydroxynaphthalene reductase; part of the gene cluster that mediates the biosynthesis of dihydroxynaphthalene (DHN)-melanin, a bluish-green pigment and a structural component of the conidial wall (PubMed:10515939, PubMed:19156203). The first step of the pathway is the production of the heptaketide naphtopyrone YWA1 by the polyketide synthase alb1 though condensation of acetyl-CoA with malonyl-CoA (PubMed:10515939). The naphtopyrone YWA1 is then converted to the pentaketide 1,3,6,8-tetrahydroxynaphthalene (1,3,6,8-THN) by the heptaketide hydrolyase ayg1 though chain-length shortening (PubMed:10515939). 1,3,6,8-THN is substrate of the hydroxynaphthalene reductase arp2 to yield scytalone (PubMed:10515939). The scytalone dehydratase arp1 then reduces scytalone to 1,3,8-THN (PubMed:10515939). 1,3,8-THN is also substrate of the hydroxynaphthalene reductase arp2 to yield vermelone (PubMed:10515939). Vermelone is further converted by the multicopper oxidase abr1 to 1,8-DHN (PubMed:10515939). Finally the laccase abr2 transforms 1,8-DHN to DHN-melanin (PubMed:10515939). DHN-melanin biosynthesis appears to be initiated in endosomes where early enzymes (abl1, ayg1, arp1 and arp2) localize, with exocytosis leading to melanin deposition on the cell surface where late enzymes (abr1 and abr2) localize (PubMed:26972005). DHN-melanin is an important structural component of the outer cell wall and is required for the presence of conidial surface hydrophobins (PubMed:19703288). DHN-melanin also plays a crucial role in fungal virulence, including a protective role against the host's immune defenses (PubMed:19156203, PubMed:20145078, PubMed:21747802, PubMed:21573171, PubMed:24818666). DHN-melanin protects also conidia against amoeba predation (PubMed:25684622). Tricyclazole and pyroquilon inhibit arp2 hydroxynaphtalene reductase activity (PubMed:19703288). Pigment biosynthesis; melanin biosynthesis. Results in brownish conidial phenotype (PubMed:19703288, PubMed:26972005). Results in an altered conidial surface with masked surface rodlet layer, leaky cell wall allowing the deposition of proteins on the cell surface and exposing the otherwise-masked cell wall polysaccharides at the surface (PubMed:24818666). Belongs to the short-chain dehydrogenases/reductases (SDR) family.