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The Novel Mechanism that Glucose and Light/Auxin Orchestrate TOR Signaling for Activation of the Root and Shoot Apexes


An light-auxin-ROP2-TOR-transcription factors E2Fa,b signaling cascade was found in Arabidopsis that coordinates with glucose(energy) signals to orchestrate plant growth and development
Research groups, directed by Prof. Yan Xiong and Prof. Tongda Xu in Shanghai Center for Plant Stress Biology(PSC), Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences recently published an article, entitled ”Differential TOR activation and cell proliferation in Arabidopsis root and shoot apexes”, in Proc Natl Acad SCi USA.2017 Feb 21. This article addressed the vital question whether and how the spatially separated shoot and root apex meristems respond to the dynamic environmental changes differentially in nature.
The developmental plasticity of plants relies on the remarkable ability of the meristems to integrate nutrient and energy availability with environmental signals. Meristems in root and shoot apexes share highly similar molecular players but are spatially separated by soil. Whether and how these two meristematic tissues have differential activation requirements for local nutrient, hormone, and environmental cues (e.g., light) remain enigmatic in photosynthetic plants. This research report that the activation of root and shoot apexes relies on distinct glucose and light signals. Glucose energy signaling is sufficient to activate target of rapamycin (TOR) kinase in root apexes. In contrast, both the glucose and light signals are required for TOR activation in shoot apexes. Strikingly, exogenously applied auxin is able to replace light to activate TOR in shoot apexes and promote true leaf development. A relatively low concentration of auxin in the shoot and high concentration of auxin in the root might be responsible for this distinctive light requirement in root and shoot apexes, because light is required to promote auxin biosynthesis in the shoot. Furthermore, this study reveal that the small GTPase ROP2 transduces light-auxin signal to activate TOR by direct interaction, which, in turn, promotes E2Fa,b transcription factors for activating cell cycle genes in shoot apexes. Consistently, constitutively activated ROP2 plants stimulate TOR in the shoot apex and cause true leaf development even without light. Together, our findings establish a pivotal hub role of TOR signaling in integrating different environmental signals to regulate distinct developmental transition and growth in the shoot and root.
This research is supported by National Natural Science Foundation of China, by the Recruitment Program of Global Experts, and funding from the Chinese Academy of Sciences.

A. Differential responses to light and glucose in shoot and root development;
B. Auxin substituted light to activate TOR in the shoot apex;
C. CA-ROP2 activated pCYCB1,1::GUS expression in the dark;
D. Model for TOR kinase integrating light/auxin and nutrition signals to control shoot and root development

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