Department of Applied Science, University of Arkansas at Little Rock, Little Rock, AR 72204, USA.
J Exp Bot. 2012 Jan;63(2):825-35. doi: 10.1093/jxb/err306. Epub 2011 Oct 11.
The phosphoinositol pathway is one of the major eukaryotic signalling pathways. The metabolite of the phosphoinositol pathway, inositol- (1,4,5) trisphosphate (InsP(3)), is a regulator of plant responses to a wide variety of stresses, including light, drought, cold, and salinity. It was found that the expression of InsP 5-ptase, the enzyme that hydrolyses InsP(3), also dramatically affects the levels of inositol phosphate metabolites and the secondary metabolites in transgenic tomato plants. Tomato plants expressing InsP 5-ptase exhibited a reduction in the levels of several important inositol phosphates, including InsP(1), InsP(2), InsP(3), and InsP(4). Reduced levels of inositol phosphates accompanied an increase in the accumulation of phenylpropanoids (rutin, chlorogenic acid) and ascorbic acid (vitamin C) in the transgenic fruits of tomato plants. The enhanced accumulation of these metabolites in transgenic tomato plants was in direct correspondence with the observed up-regulation of the genes that express the key enzymes of ascorbic acid metabolism (myo-inositol oxygenase, MIOX; L-galactono-γ-lactone dehydrogenase, GLDH) and phenylpropanoid metabolism (chalcone synthase, CHS1; cinnamoyl-CoA shikimate/quinate transferase, HCT). To understand the molecular links between the activation of different branches of plant metabolism and InsP(3) reduction in tomato fruits, the expression of transcription factors known to be involved in light signalling was analysed by real-time RT-PCR. The expression of LeHY5, SIMYB12, and LeELIP was found to be higher in fruits expressing InsP 5-ptase. These results suggest possible interconnections between phosphoinositol metabolism, light signalling, and secondary metabolism in plants. Our study also revealed the biotechnological potential for the genetic improvement of crop plants by the manipulation of the phosphoinositol pathway.
磷酸肌醇途径是真核生物信号转导的主要途径之一。磷酸肌醇途径的代谢产物肌醇-（1,4,5）三磷酸（InsP(3)）是植物对多种胁迫（包括光、干旱、寒冷和盐度）反应的调节剂。研究发现，水解 InsP(3)的酶 InsP 5-ptase 的表达也会显著影响肌醇磷酸代谢物和转基因番茄植物次生代谢物的水平。表达 InsP 5-ptase 的番茄植物表现出几种重要的肌醇磷酸（包括 InsP(1)、InsP(2)、InsP(3)和 InsP(4)）水平降低。肌醇磷酸水平降低伴随着苯丙烷类（芦丁、绿原酸）和抗坏血酸（维生素 C）在转基因番茄果实中的积累增加。这些代谢物在转基因番茄植物中的积累增强与观察到的关键酶基因的表达上调直接相关，这些基因表达抗坏血酸代谢（肌醇氧化酶，MIOX；L-半乳糖酸-γ-内酯脱氢酶，GLDH）和苯丙烷代谢（查尔酮合酶，CHS1；肉桂酰辅酶 A 莽草酸/奎宁酸转移酶，HCT）。为了了解植物代谢不同分支的激活与番茄果实中 InsP(3)减少之间的分子联系，通过实时 RT-PCR 分析了已知参与光信号转导的转录因子的表达。发现表达 InsP 5-ptase 的果实中 LeHY5、SIMYB12 和 LeELIP 的表达更高。这些结果表明磷酸肌醇代谢、光信号和植物次生代谢之间可能存在相互联系。我们的研究还揭示了通过操纵磷酸肌醇途径对作物进行遗传改良的生物技术潜力。
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