A novel senescence‐associated gene encoding γ‐aminobutyric acid (GABA):pyruvate transaminase is upregulated during rice leaf senescence

Abstract

The gene Osl2, which is specifically upregulated during leaf senescence in rice (Oryza sativa L. cv. Tainong 67), was cloned and functionally characterized. The protein coding region of the gene consists of 19 exons encoding 516 amino acids, with a putative mitochondrial targeting sequence and conserved sequence of the pyridoxal 5 0 -phosphate-binding domain. The recombinant Osl2 fusion protein over-expressed in Escherichia coli displays pyruvate-dependent g-aminobuty-ric acid (GABA) transaminase (EC 2.6.1.19) activity. Examination of the expression patterns of the Osl2 gene in rice reveals that Osl2-specific transcripts are induced in the senescing leaves. The temporal profile of Osl2 protein accumulation is correlated with that of pyruvate-dependent GABA transaminase activity in rice leaves, with the highest expression level at the S3 senescent stage. The potential role for GABA transaminase during rice leaf senescence is discussed.

TheArabidopsis onset of leaf death5Mutation of Quinolinate Synthase Affects Nicotinamide Adenine Dinucleotide Biosynthesis and Causes Early Ageing

“…One of the most intriguing metabolites that show an age-related accumulation in both the wild type and old5 is GABA. Studies on Osl2, a mitochondrial GABA transaminase in rice (Oryza sativa) (Ansari et al, 2005), suggested a switch in metabolism at the onset of senescence. Next to that, in plants as well as in animals, the GABA shunt is upregulated in times of high respiratory demand (Sweetlove et al, 2007;Fait et al, 2008).…”

Does GABA increase the efficiency of symbiotic N2fixation in legumes?

“…24 Additionally, in the recent years, the possibility that GABA might be involved in regulating plant growth and development has been raised. Several plant development processes has been suggested including pollen tube growth, 25 senescence, 26 reproduction, 25 fertilization 27 and are numerous environmental effects causing a decrease in symbiotic N 2 fixation activity. In many cases it has been assumed that such decrease in N 2 fixation could induce growth retardation of the legume plant as well as the plant demand for symbiotically fixed N. 6 There is a growing body of evidence indicating that symbiotic N 2 fixation of legumes is tightly regulated by the host N-demand which is mediated through N-feedback mechanism.…”

The cell death factor, cell wall elicitor of rice blast fungus (Magnaporthe grisea) causes metabolic alterations including GABA shunt in rice cultured cells

“…The amount of GABA in the resulting supernatant was measured by the CE/MS method described above. Pyruvate-dependent GABA-T (GABA-TP) activity was measured according to the method of Ansari et al, 27 with minor modifications. The extract was added to a reaction mixture (pH 8.2) containing 50 mM Tris-HCl, 1.5 mM DTT, 0.5 mM EDTA, 10% glycerol, 10 mM GABA and 0.1 mM PLP.…”