Catalyzes the oxidation of (R)-2-hydroxyglutarate to 2-oxoglutarate. May be involved in the catabolism of propionyl-CoA derived from beta-oxidation. Involved in degradation of lysine for the supply of carbon and electrons to the ETF/ETFQO complex during dark-induced sugar starvation. (R)-2-hydroxyglutarate + A = 2-oxoglutarate + AH2 Binds 1 FAD per monomer. Very low activity toward D-lactate, D-2-hydroxybutyrate and meso-tartrate. Does not efficiently use cytochrome c as electron acceptor and is not able to transfer electrons to NAD or NADP. Optimum pH is 8.5-9.5. Homodimer. By dark-induced senescence. No visible phenotype when grown under standard conditions. Belongs to the FAD-binding oxidoreductase/transferase type 4 family. Intron retention.