Short-chain dehydrogenase/reductase; part of the gene cluster that mediates the biosynthesis of fusarubins, highly pigmented naphthoquinones responsible for the coloration of the fruiting bodies (PubMed:22492438, PubMed:23825955). The non-reducing polyketide synthase FSR1 is responsible for the condensation of seven acetyl-CoA units to yield a haptaketide (PubMed:22492438). After rings A and B are formed by aldol-type cyclization, the PKS-derived product is released as 6-O-demethylfusarubinaldehyde (PubMed:22492438). Then, two hydroxyl groups at C-5 and C-10 are incorporated by FSR3, and simultaneously hydroxyl groups at C-6 and C-8 are methylated by FSR2 (PubMed:22492438). The aldehyde is, on the one hand, reduced by FSR3 to 8-O-methylfusarubin alcohol, which equilibrates mainly with 8-O-methylfusarubin and only small amounts of 8-O-methylnectriafurone (PubMed:22492438). On the other hand, the aldehyde can be oxidized to form 8-O-methylfusarubinic acid, a reaction driven by FSR3 equilibrating with 8-O-methylfusarubinlactone, finally resulting in 8-O-methylanhydrofusarubinlactol after a further reduction step and loss of water (PubMed:22492438). 8-O-Methylfusarubinic acid can also undergo decarboxylation, resulting in 8-O-methyl-13-hydroxynorjavanicin after another hydroxylation step at C-13 (PubMed:22492438). Both steps are most likely also accomplished by FSR3 (PubMed:22492438). No enzymatic function has been determined so far for either FSR4 and FSR5 (PubMed:22492438). Their deletion does not alter the product spectrum, but the possibility that they catalyze specific enzymatic steps during perithecium development cannot be ruled out (PubMed:22492438). FSR4 might possess a regulatory function in the biosynthesis of fusarubins (PubMed:22492438). Expression is induced in presence of sodium nitrate, and repressed by glutamine (PubMed:22492438). Does nor affect the production of the fusarubins (PubMed:22492438). Belongs to the short-chain dehydrogenases/reductases (SDR) family.