Biochemical mechanism on GABA accumulation during fruit development in tomato
Biochemical mechanism on GABA accumulation during fruit development in tomato
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DOI：
10.1093/pcp/pcn113
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发表时间：
2008-09-01
影响因子：
4.9
通讯作者：
Ezura, Hiroshi
中科院分区：
文献类型：
--
作者：
Akihiro, Takashi;Koike, Satoshi;Ezura, Hiroshi
人们发现，在成熟期之前，番茄（Solanum lycopersicum）果实中积累了大量的γ-氨基丁酸（GABA）。此后不久，GABA 在破坏阶段后迅速分解代谢。我们筛选了富含 GABA 的番茄品种“DG03-9”，该品种在破碎阶段后没有表现出快速的 GABA 分解代谢。尽管水果中 GABA 的超积累和快速分解代谢是众所周知的，但其机制尚不清楚。为了阐明这些机制，我们对“Micro-Tom”和“DG03-9”果实进行了比较研究，分析 GABA 生物合成和分解代谢相关酶的基因表达水平、蛋白质水平和酶活性水平。在GABA积累过程中，我们发现GABA含量与SlGAD2和SlGAD3的表达水平呈正相关。这两个基因都编码谷氨酸脱羧酶（GAD），这是 GABA 生物合成的关键酶。在 GABA 分解代谢过程中，我们发现 GABA 含量与 α-酮戊二酸依赖性 GABA 转氨酶 (GABA-TK) 的酶活性之间存在很强的相关性。分别由GABA和谷氨酸合成的谷氨酸和天冬氨酸的含量随着GABA-TK酶活性的升高而增加。 GABA-TK 是动物中 GABA 转氨酶的主要形式，并且似乎是植物中的次要形式。在‘DG03-9’果实中，GAD酶活性延长至成熟期，而GABA-TK活性显着较低。综上所述，我们的结果表明，GAD 和 GABA-TK 分别在番茄果实中的 GABA 积累和分解代谢中发挥着至关重要的作用。
A large amount of gamma-aminobutyric acid (GABA) was found to accumulate in tomato (Solanum lycopersicum) fruits before the breaker stage. Shortly thereafter, GABA was rapidly catabolized after the breaker stage. We screened the GABA-rich tomato cultivar 'DG03-9' which did not show rapid GABA catabolism after the breaker stage. Although GABA hyperaccumulation and rapid catabolism in fruits is well known, the mechanisms are not clearly understood. In order to clarify these mechanisms, we performed comparative studies of 'Micro-Tom' and 'DG03-9' fruits for the analysis of gene expression levels, protein levels and enzymatic activity levels of GABA biosynthesis- and catabolism-related enzymes. During GABA accumulation, we found positive correlations among GABA contents and expression levels of SlGAD2 and SlGAD3. Both of these genes encode glutamate decarboxylase (GAD) which is a key enzyme of GABA biosynthesis. During GABA catabolism, we found a strong correlation between GABA contents and enzyme activity of alpha-ketoglutarate-dependent GABA transaminase (GABA-TK). The contents of glutamate and aspartate, which are synthesized from GABA and glutamate, respectively, increased with elevation of GABA-TK enzymatic activity. GABA-TK is the major GABA transaminase form in animals and appears to be a minor form in plants. In 'DG03-9' fruits, GAD enzymatic activity was prolonged until the ripening stage, and GABA-TK activity was significantly low. Taken together, our results suggest that GAD and GABA-TK play crucial roles in GABA accumulation and catabolism, respectively, in tomato fruits.