Identification of Photorespiratory Glutamate: Glyoxylate Aminotransferase (GGAT) Gene in Arabidopsis

Abstract

In the photorespiratory process, peroxisomal glutamate: glyoxylate aminotransferase (GGAT) catalyzes the reaction of glutamate and glyoxylate to 2-oxoglutalate and glycine. Although GGAT was thought to have essential roles for the transamination to photorespiratory cycles, the gene encoding GGAT has not been identified. We isolated a T-DNA insertion knockout line of alanine 2-oxoglutarate aminotransferase (AOAT)-like protein (aoat1-1). In aoat1-1 the activity of GGAT was reduced drastically. The growth rate of aoat1-1 was repressed under normal light, though differences were slight under lower light or high CO₂ (0.3%) conditions. These phenotypes resembled to photorespiration deficient mutants. aoat1-1 displayed an increase of glutamate levels and a reduction of serine levels. Based on these results it was concluded that AOAT1 functions as photorespiratory GGAT.