Glucose-TOR signalling orchestrates metabolic transcriptome and meristem establishment
Yan Xiong, Matthew McMcormark, Qi Hall, Chengbin Xiang & Jen Sheen

Department of Molecular Biology, Massachusetts General Hospital, and Department of Genetics, Harvard Medical School, Boston,USA.
School of Life Science, University of Science and Technology of China, Hefei, China.
Corresponding Author: Yan Xiong, Tel (+8601) 515-771-2910, E-mail: xiong@molbio.mgh.harvard.edu

Abstract
Meristems encompass stem/progenitor cells that sustain postembryonic growth of all plant organs. How meristems are established and stimulated by nutrient signaling remains enigmatic in photosynthetic plants. Combing chemical manipulations and chemical genetics at the photoautotrophic transition checkpoint, we reveal that shoot photosynthesis drives long-distance glucose-target-of-rapamycin (TOR) signaling relays through glycolysis and mitochondrial bioenergetics to control root meristem establishment and accelerate growth, which is decoupled from direct glucose sensing, growth-hormone signaling, and stem-cell maintenance. Surprisingly, glucose-TOR signaling dictates transcriptional reprogramming of remarkable gene sets involved in cell cycle, transcription, signaling, metabolism, transport and folding. Systems, cellular and genetic analyses uncover TOR phosphorylation of E2Fa transcription factor for an unconventional activation of S-phase genes, and glucose-insensitive e2fa root-meristem defects. Our findings establish pivotal roles of glucose-TOR signaling in unprecedented transcriptional networks wiring central metabolism/biosynthesis for energy/biomass production, and integrating localized stem/progenitor-cell proliferation through inter-organ nutrient signaling to control developmental transition and growth.

Key Words: Target of rapamycin, glucose, mitochondrial bioenergetics, meristem, photoautotrophic transition, inter-organ signaling, E2Fa transcription factor.