Fukushima Atsushi, Iwasa Mami, Nakabayashi Ryo, Kobayashi Makoto, Nishizawa Tomoko, Okazaki Yozo, Saito Kazuki, Kusano Miyako
RIKEN Center for Sustainable Resource ScienceYokohama, Japan.
Nissan Chemical Industries, Ltd.Funabashi, Japan.
Front Plant Sci. 2017 Aug 28;8:1464. doi: 10.3389/fpls.2017.01464. eCollection 2017.
Plants possess highly sensitive mechanisms that monitor environmental stress levels for a dose-dependent fine-tuning of their growth and development. Differences in plant responses to severe and mild abiotic stresses have been recognized. Although many studies have revealed that glutathione can contribute to plant tolerance to various environmental stresses, little is known about the relationship between glutathione and mild abiotic stress, especially the effect of stress-induced altered glutathione levels on the metabolism. Here, we applied a systems biology approach to identify key pathways involved in the gene-to-metabolite networks perturbed by low glutathione content under mild abiotic stress in . We used glutathione synthesis mutants ( and ) and plants overexpressing the gene encoding γ-glutamylcysteine synthetase, the first enzyme of the glutathione biosynthetic pathway. The plants were exposed to two mild stress conditions-oxidative stress elicited by methyl viologen and stress induced by the limited availability of phosphate. We observed that the mutants and transgenic plants showed similar shoot growth as that of the wild-type plants under mild abiotic stress. We then selected the synthesis mutants and performed multi-platform metabolomics and microarray experiments to evaluate the possible effects on the overall metabolome and the transcriptome. As a common oxidative stress response, several flavonoids that we assessed showed overaccumulation, whereas the mild phosphate stress resulted in increased levels of specific kaempferol- and quercetin-glycosides. Remarkably, in addition to a significant increased level of sugar, osmolytes, and lipids as mild oxidative stress-responsive metabolites, short-chain aliphatic glucosinolates over-accumulated in the mutants, whereas the level of long-chain aliphatic glucosinolates and specific lipids decreased. Coordinated gene expressions related to glucosinolate and flavonoid biosynthesis also supported the metabolite responses in the mutant. Our results suggest that glutathione synthesis mutants accelerate transcriptional regulatory networks to control the biosynthetic pathways involved in glutathione-independent scavenging metabolites, and that they might reconfigure the metabolic networks in primary and secondary metabolism, including lipids, glucosinolates, and flavonoids. This work provides a basis for the elucidation of the molecular mechanisms involved in the metabolic and transcriptional regulatory networks in response to combined low glutathione content with mild oxidative and nutrient stress in .
植物拥有高度敏感的机制，可监测环境胁迫水平，以便对其生长和发育进行剂量依赖性的精细调节。人们已经认识到植物对严重和轻度非生物胁迫的反应存在差异。尽管许多研究表明谷胱甘肽有助于植物耐受各种环境胁迫，但关于谷胱甘肽与轻度非生物胁迫之间的关系，尤其是胁迫诱导的谷胱甘肽水平变化对代谢的影响，人们所知甚少。在此，我们应用系统生物学方法来确定在轻度非生物胁迫下，低谷胱甘肽含量扰乱的基因到代谢物网络中涉及的关键途径。我们使用了谷胱甘肽合成突变体（和）以及过表达编码γ-谷氨酰半胱氨酸合成酶（谷胱甘肽生物合成途径的第一种酶）基因的植物。将这些植物暴露于两种轻度胁迫条件下——甲基紫精引发的氧化胁迫和磷酸盐供应有限诱导的胁迫。我们观察到，在轻度非生物胁迫下，突变体和转基因植物的地上部生长与野生型植物相似。然后，我们选择了合成突变体并进行多平台代谢组学和微阵列实验，以评估对整体代谢组和转录组的可能影响。作为一种常见的氧化应激反应，我们评估的几种黄酮类化合物显示出过度积累，而轻度磷酸盐胁迫导致特定山奈酚和槲皮素糖苷水平升高。值得注意的是，除了作为轻度氧化应激反应代谢物的糖、渗透保护剂和脂质水平显著增加外，短链脂肪族芥子油苷在突变体中过度积累，而长链脂肪族芥子油苷和特定脂质的水平则下降。与芥子油苷和黄酮类生物合成相关的协调基因表达也支持了突变体中的代谢物反应。我们的结果表明，谷胱甘肽合成突变体加速转录调控网络，以控制参与非谷胱甘肽依赖性清除代谢物的生物合成途径，并且它们可能重新配置初级和次级代谢中的代谢网络，包括脂质、芥子油苷和黄酮类化合物。这项工作为阐明在中低谷胱甘肽含量与轻度氧化和营养胁迫相结合时，代谢和转录调控网络中涉及的分子机制提供了基础。
