Single-component hydroxylase that is part of the gamma-resorcylate (GRA) degradation pathway. GRA is initially converted by GRA decarboxylase to resorcinol, which is hydroxylated by resorcinol 4-hydroxylase. H(+) + NADH + O2 + resorcinol = benzene-1,2,4-triol + H2O + NAD(+) The mutant bacteria is unable to grow on GRA (PubMed:26319878). Only 25% of the resorcinol is degraded compared to wild-type (PubMed:26319878).