Mitochondrial succinic-semialdehyde dehydrogenase of the γ-aminobutyrate shunt is required to restrict levels of reactive oxygen intermediates in plants

Abstract

The ␥-aminobutyrate (GABA) shunt is a metabolic pathway that bypasses two steps of the tricarboxylic acid cycle, and it is present in both prokaryotes and eukaryotes. In plants the pathway is composed of the calcium͞calmodulin-regulated cytosolic enzyme glutamate decarboxylase and the mitochondrial enzymes GABA transaminase and succinic-semialdehyde dehydrogenase (SSADH). The activity of the GABA shunt in plants is rapidly enhanced in response to various biotic and abiotic stresses. However the physiological role of this pathway remains obscure. To elucidate its role in plants, we analyzed Arabidopsis T-DNA knockout mutants of SSADH, the ultimate enzyme of the pathway. Four alleles of the ssadh mutation were isolated, and these exhibited a similar phenotype. When exposed to white light (100 mol of photons per m 2 per s), they appear dwarfed with necrotic lesions. Detailed spectrum analysis revealed that UV-B has the most adverse effect on the mutant phenotype, whereas photosynthetic active range light has a very little effect. The ssadh mutants are also sensitive to heat, as they develop necrosis when submitted to such stress. Moreover, both UV and heat cause a rapid increase in the levels of hydrogen peroxide in the ssadh mutants, which is associated with enhanced cell death. Surprisingly, our study also shows that trichomes are hypersensitive to stresses in ssadh mutants. Our work establishes a role for the GABA shunt in preventing the accumulation of reactive oxygen intermediates and cell death, which appears to be essential for plant defense against environmental stress.

Genetic approaches towards overcoming water deficit in plants - special emphasis on LEAs

“…Plants overcome the ROS mediated stress response either by preventing the accumulation of ROS or by effectively eliminating the ROS thus formed e.g. The gamma-amino butyrate (GABA) shunt prevents the accumulation of ROS and has been implicated in plant defense against environmental stress (Bouche et al, 2003). Elimination of ROS is achieved by antioxidant compounds such as ascorbic acid, glutathione, thioredoxin and carotenoids, and by ROS scavenging enzymes (e.g.…”

Significant improvement of stress tolerance in tobacco plants by overexpressing a stress-responsive aldehyde dehydrogenase gene from maize (Zea mays)

“…A mitochondria-localized ALDH5F1 encodes a succinic semialdehyde dehydrogenase and constitutes a member of the c-aminobutyric acid shunt in Arabidopsis (Busch and Fromm 1999). Disrupted ALDH5F1 results in an enhanced sensitivity to both UV-B light and heat stress (Bouché et al 2003). Another mitochondrial D 1 -pyrroline-5-carboxylate dehydrogenase probably participated in preventing proline toxicity (Deuschle et al 2001).…”

An extensive microarray analysis of AAL-toxin-induced cell death in Arabidopsis thaliana brings new insights into the complexity of programmed cell death in plants

“…It encodes glutamate decarboxylase, a Ca 2+ /calmodulin-dependent enzyme that converts glutamate to g-aminobutiric acid (GABA) [49]. GABA is regarded as a stress molecule and participates in the so-called GABA shunt, a pathway that is essential for restriction of levels of ROS in plants [50]. We were surprised to see levels of a number of droughtand low-temperature-induced proteins, including LTI78 and the transcription factor DREB1C, going down already at the first time point.…”