Journal
PLANT AND CELL PHYSIOLOGY
Volume 56, Issue 8, Pages 1533-1545Publisher
OXFORD UNIV PRESS
DOI: 10.1093/pcp/pcv075
Keywords
Fruit; GABA; GAD; Molecular breeding; RNAi; Tomato
Categories
Funding
- Japan-France Joint Laboratory Project
- Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan
- Research and Development Program for New Bio-industry Initiatives, Bio-oriented Technology Research Advancement Institution (BRAIN)
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Tomato (Solanum lycopersicum) can accumulate relatively high levels of g-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.
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