期刊
PLANT CELL REPORTS
卷 36, 期 1, 页码 103-116出版社
SPRINGER
DOI: 10.1007/s00299-016-2061-4
关键词
E8 promoter; Fruit ripening; GABA; HSP terminator; Tomato
资金
- Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan
- Japan-France Joint Laboratory Project
- Research and Development Program for New Bio-industry Initiative, Bio-oriented Technology Research Advancement Institution (BRAIN)
The C-terminal extension region of SlGAD3 is likely involved in autoinhibition, and removing this domain increases GABA levels in tomato fruits. gamma-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 (SlGAD3 Delta C (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 SlGAD3 Delta C (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, SlGAD3 Delta C (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.
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