Capturing the phosphorylation and protein interaction landscape of the plant TOR kinase

Meristems encompass stem/progenitor cells that sustain postembryonic growth of all plant organs. How meristems are activated and sustained by nutrient signalling remains enigmatic in photosynthetic plants. Combining chemical manipulations and chemical genetics at the photoautotrophic transition checkpoint, we reveal that shoot photosynthesis-derived glucose drives target-of-rapamycin (TOR) signalling relays through glycolysis and mitochondrial bioenergetics to control root meristem activation, which is decoupled from direct glucose sensing, growth-hormone signalling, and stem-cell maintenance. Surprisingly, glucose-TOR signalling dictates transcriptional reprogramming of remarkable gene sets involved in central and secondary metabolism, cell cycle, transcription, signalling, 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-signalling defects in e2fa root meristems. Our findings establish pivotal roles of glucose-TOR signalling in unprecedented transcriptional networks wiring central metabolism and biosynthesis for energy and biomass production, and integrating localized stem/progenitor-cell proliferation through inter-organ nutrient coordination to control developmental transition and growth.

Comparative sequence analysis has significantly altered our view on the complexity of genome organization and gene functions in different kingdoms. PLAZA 3.0 is designed to make comparative genomics data for plants available through a user-friendly web interface. Structural and functional annotation, gene families, protein domains, phylogenetic trees and detailed information about genome organization can easily be queried and visualized. Compared with the first version released in 2009, which featured nine organisms, the number of integrated genomes is more than four times higher, and now covers 37 plant species. The new species provide a wider phylogenetic range as well as a more in-depth sampling of specific clades, and genomes of additional crop species are present. The functional annotation has been expanded and now comprises data from Gene Ontology, MapMan, UniProtKB/Swiss-Prot, PlnTFDB and PlantTFDB. Furthermore, we improved the algorithms to transfer functional annotation from well-characterized plant genomes to other species. The additional data and new features make PLAZA 3.0 (http://bioinformatics.psb.ugent.be/plaza/) a versatile and comprehensible resource for users wanting to explore genome information to study different aspects of plant biology, both in model and non-model organisms.

All living organisms rely on nutrients to sustain cell metabolism and energy production, which in turn need to be adjusted based on available resources. The evolutionarily conserved target of rapamycin (TOR) protein kinase is a central regulatory hub that connects environmental information about the quantity and quality of nutrients to developmental and metabolic processes in order to maintain cellular homeostasis. TOR is activated by both nitrogen and carbon metabolites and promotes energy-consuming processes such as cell division, mRNA translation, and anabolism in times of abundance while repressing nutrient remobilization through autophagy. In animals and yeasts, TOR acts antagonistically to the starvation-induced AMP-activated kinase (AMPK)/sucrose nonfermenting 1 (Snf1) kinase, called Snf1-related kinase 1 (SnRK1) in plants. This review summarizes the immense knowledge on the relationship between TOR signaling and nutrients in nonphotosynthetic organisms and presents recent findings in plants that illuminate the crucial role of this pathway in conveying nutrient-derived signals and regulating many aspects of metabolism and growth.