RRC ID 49501
Author Takayama M, Matsukura C, Ariizumi T, Ezura H.
Title Activating glutamate decarboxylase activity by removing the autoinhibitory domain leads to hyper γ-aminobutyric acid (GABA) accumulation in tomato fruit.
Journal Plant Cell Rep
Abstract KEY MESSAGE:The C-terminal extension region of SlGAD3 is likely involved in autoinhibition, and removing this domain increases GABA levels in tomato fruits. γ-Aminobutyric acid (GABA) is a ubiquitous non-protein amino acid with several health-promoting benefits. In many plants including tomato, GABA is synthesized via decarboxylation of glutamate in a reaction catalyzed by glutamate decarboxylase (GAD), which generally contains a C-terminal autoinhibitory domain. We previously generated transgenic tomato plants in which tomato GAD3 (SlGAD3) was expressed using the 35S promoter/NOS terminator expression cassette (35S-SlGAD3-NOS), yielding a four- to fivefold increase in GABA levels in red-ripe fruits compared to the control. In this study, to further increase GABA accumulation in tomato fruits, we expressed SlGAD3 with (SlGAD3 OX ) or without (SlGAD3ΔC OX ) a putative autoinhibitory domain in tomato using the fruit ripening-specific E8 promoter and the Arabidopsis heat shock protein 18.2 (HSP) terminator. Although the GABA levels in SlGAD3 OX fruits were equivalent to those in 35S-SlGAD3-NOS fruits, GABA levels in SlGAD3ΔC OX fruits increased by 11- to 18-fold compared to control plants, indicating that removing the autoinhibitory domain increases GABA biosynthesis activity. Furthermore, the increased GABA levels were accompanied by a drastic reduction in glutamate and aspartate levels, indicating that enhanced GABA biosynthesis affects amino acid metabolism in ripe-fruits. Moreover, SlGAD3ΔC OX fruits exhibited an orange-ripe phenotype, which was associated with reduced levels of both carotenoid and mRNA transcripts of ethylene-responsive carotenogenic genes, suggesting that over activation of GAD influences ethylene sensitivity. Our strategy utilizing the E8 promoter and HSP terminator expression cassette, together with SlGAD3 C-terminal deletion, would facilitate the production of tomato fruits with increased GABA levels.
Volume 36(1)
Pages 103-116
Published 2017-1-1
DOI 10.1007/s00299-016-2061-4
PII 10.1007/s00299-016-2061-4
PMID 27704232
MeSH Amino Acid Sequence Amino Acids / metabolism Biosynthetic Pathways / genetics Carotenoids / biosynthesis Enzyme Activation Ethylenes / metabolism Fruit / enzymology* Gene Expression Regulation, Plant Genes, Plant Glutamate Decarboxylase / chemistry* Glutamate Decarboxylase / genetics Glutamate Decarboxylase / metabolism* Pigmentation / genetics Plants, Genetically Modified Protein Domains RNA, Messenger / genetics RNA, Messenger / metabolism Sequence Alignment Sequence Deletion* Solanum lycopersicum / enzymology* Solanum lycopersicum / genetics gamma-Aminobutyric Acid / metabolism*
IF 3.825
Times Cited 16