Abstract
The disruption of the succinic semialdehyde dehydrogenase (SSADH) function in Arabidopsis leads to aberrant growth phenotype. In human, the SSADH malfunction leads to a condition known as γ-hydroxybutyrate (GHB) aciduria. It is characterized by the accumulation of GHB as well as abnormal growth. GHB aciduria is treated pharmacologically with compounds analogous to gamma-aminubutyrate (GABA). One of these compounds called vagabatrin effectively suppressed the ssadh phenotype in Arabidopsis. Furthermore, the Arabidopsis ssadh phenotype has been suppressed genetically by simultaneous mutation in the POP2 gene. In the present study, the presence of alternative solutions for suppression of the ssadh phenotype was investigated. For that, four ethyl methanesulfonate treated ssadh lines namely 7D, 13J, 17J and 21H were characterized phenotypically and chemotypically. Three- week-old plants of the suppressor lines grew much better than the parent ssadh line and resembled the wild type. The suppressor lines also accumulated reduced amounts of GABA and GHB. PCR based mapping using Sequence Characterized Amplified Region (SCAR) markers located the mutations to chromosome 2 and chromosome 5, suggesting the involvement of at least two mutations in suppression of the ssadh phenotype. Deep whole-genome sequencing of line 17J identified several mutations that induced amino acid change, frame shift and a stop codon. The findings showed that there are more possibilities to suppress the ssadh phenotype; furthermore, it provides an opportunity to identify genes that interact with the GABA shunt. Key words: Gamma-aminubutyrate (GABA), shunt; succinic semialdehyde dehydrogenase (SSADH) mapping, Arabidopsis, succinic semialdehyde (SSA), γ-hydroxybutyrate (GHB).
Highlights
Succinic semialdehyde dehydrogenase (SSADH) is a Gamma-aminubutyrate (GABA)-shunt enzyme that catalyzes the oxidation of succinic semialdehyde (SSA) to succinate in the presence of NAD+
The findings showed that there are more possibilities to suppress the ssadh phenotype; it provides an opportunity to identify genes that interact with the GABA shunt
The only known way of suppressing of the ssadh phenotype in Arabidopsis is through mutations in POP2 gene
Summary
Succinic semialdehyde dehydrogenase (SSADH) is a Gamma-aminubutyrate (GABA)-shunt enzyme that catalyzes the oxidation of succinic semialdehyde (SSA) to succinate in the presence of NAD+. Its genome contains a single copy of SSADH encoding gene (Busch and Fromm, 1999) Knockout of this single gene leads to an accumulation of reactive oxygen species (ROS), a stunted growth (dwarfism), a necrosis on leaves and hypersensitivity to environmental stresses (Fait et al, 2004; Bouche et al, 2003). This abnormal growth phenotype was associated with an accumulation of gamma hydroxybutyric acid (GHB) and hydrogen peroxide in tissues (Fait et al, 2004). Deficiency in SSADH activity causes a disorder called GHB aciduria, which is manifested by a high level of GHB in the physiological fluids (Jakobs et al, 1981; Hogema et al, 2001)
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