May supply 2-oxoglutarate for amino acid biosynthesis and ammonia assimilation via the glutamine synthetase/glutamate synthase (GS/GOGAT) pathway. May be involved in the production of NADPH to promote redox signaling or homeostasis in response to oxidative stress, or redox signaling linked to defense responses. D-threo-isocitrate + NADP(+) = 2-oxoglutarate + CO2 + NADPH Binds 1 Mg(2+) or Mn(2+) ion per subunit. Slight reduction in plant growth. Constitutive expression of pathogenesis-related genes and enhanced resistance to the bacterial pathogen P.syringae pv. tomato. Belongs to the isocitrate and isopropylmalate dehydrogenases family.