Abstract
γ-aminobutyric acid transaminase (GABA-T) catalyses the conversion of GABA to succinic semialdehyde. Tomato has three genes for GABA-T. Each isoform shows different subcellular localization. These all enzymes showed pyruvate- and glyoxylate-dependent activities (Clark et al., 2009). Rice (O.sativa) is composed of four GABA-T gene families. Here, we report subcellular localization and enzymatic characterization for rice GABA-Ts. We fused full-length cDNAs for OsGABA-T1, OsGABA-T2, OsGABA-T3 each to the 5'-proximal site of the GFP in-frame. For OsGABA-T4, a coding region from first to second initiation codon in it was inserted in the 5'-upstream of the GFP. Transient expression assay of these GFP fusion plasmids in Allium epidermal and Vicia guard cells revealed that both OsGABA-T1 and OsGABA-T2 are localized in mitochondria. OsGABA-T3::GFP was targeted to plastids and cytosol as well as mitochondria. OsGABA-T4 was observed only in cytosol. Like tomato, these enzymes all acted in pyruvate- and glyoxylate-dependent manner. Enzymatic activities of OaGABA-T1 and OsGABA-T3 were relatively the same, while that of OsGABA-T2 was only one to two % of those of the former two enzymes.
