title: Tomato Glutamate Decarboxylase Genes SlGAD2 and SlGAD3 Play Key Roles in Regulating γ-Aminobutyric Acid Levels in Tomato (Solanum lycopersicum).
abstract: Tomato (Solanum lycopersicum) can accumulate relatively high levels of γ-aminobutyric acid (GABA) during fruit development. However, the molecular mechanism underlying GABA accumulation and its physiological function in tomato fruits remain elusive. We previously identified three tomato genes (SlGAD1, SlGAD2 and SlGAD3) encoding glutamate decarboxylase (GAD), likely the key enzyme for GABA biosynthesis in tomato fruits. In this study, we generated transgenic tomato plants in which each SlGAD was suppressed and those in which all three SlGADs were simultaneously suppressed. A significant decrease in GABA levels, i.e. 50-81% compared with wild-type (WT) levels, was observed in mature green (MG) fruits of the SlGAD2-suppressed lines, while a more drastic reduction (up to <10% of WT levels) was observed in the SlGAD3- and triple SlGAD-suppressed lines. These findings suggest that both SlGAD2 and SlGAD3 expression are crucial for GABA biosynthesis in tomato fruits. The importance of SlGAD3 expression was also confirmed by generating transgenic tomato plants that over-expressed SlGAD3. The MG and red fruits of the over-expressing transgenic lines contained higher levels of GABA (2.7- to 5.2-fold) than those of the WT. We also determined that strong down-regulation of the SlGADs had little effect on overall plant growth, fruit development or primary fruit metabolism under normal growth conditions.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Mariko
authors.initials: M
authors.lastname: Takayama
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Koike
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan RIKEN Center for Sustainable Resource Science, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Miyako
authors.initials: M
authors.lastname: Kusano
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Chiaki
authors.initials: C
authors.lastname: Matsukura
authors.affiliation: RIKEN Center for Sustainable Resource Science, Yokohama, Kanagawa 230-0045, Japan Graduate School of Pharmaceutical Sciences, Chiba University, Chiba-shi, Chiba 260-0856, Japan.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Saito
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Tohru
authors.initials: T
authors.lastname: Ariizumi
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan ezura@gene.tsukuba.ac.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ezura
mesh_terms: D015536:Down-Regulation; D005638:Fruit / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D018506:Gene Expression Regulation, Plant; D005968:Glutamate Decarboxylase / Q000235:genetics* / Q000378:metabolism; D018551:Solanum lycopersicum / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1; C401141:glutamate decarboxylase 2
keywords: Fruit; GABA; GAD; Molecular breeding; RNAi; Tomato