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

Nicolas Bouché, Aaron Fait, David Bouchez, Simon G. Møller, Hillel Fromm

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329 Scopus citations

Abstract

The γ-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 calcium/calmodulin-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 μmol of photons per m2 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.

Original languageEnglish
Pages (from-to)6843-6848
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume100
Issue number11
DOIs
StatePublished - 27 May 2003
Externally publishedYes

ASJC Scopus subject areas

  • General

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