Activation of TOR signaling by diverse nitrogen signals in plants

Growth control in eukaryotes depends on the TOR kinase, which integrates energy and nutrient signals. In this issue of Developmental Cell, Liu et al. demonstrate that, plants, inorganic nitrogen amino acids activate via GTPase ROP2 to promote cell proliferation leaf growth shoot. All cells must align developmental decisions with availability nutrients needed support growth. eukaryotic organisms, job assessing cellular status falls a highly conserved protein kinase called (target rapamycin) (Kim Guan, 2019Kim J. Guan K.L. mTOR as central hub signalling growth.Nat. Cell Biol. 2019; 21: 63-71Crossref PubMed Scopus (385) Google Scholar). animals, wide range upstream signals, including availability, factor levels, energy, stress. activation promotes gene expression biosynthetic cascades anabolism proliferation. A similar role for node controlling has also been established plants (Wu al., 2019Wu Y. Shi L. Li Fu Xiong Sheen Integration nutrient, light, hormone plants.J. Exp. Bot. 70: 2227-2238Crossref (51) Scholar), but how signals contribute remains largely unknown. Nitrogen is an essential macronutrient acquired primarily (nitrate ammonia) from soil. 2021Liu Duan X. Zhao Ding W. Wang Diverse convergent ROP2-TOR signaling Arabidopsis.Dev. Cell. 2021; 56 (this issue): 1283-1295Abstract Full Text PDF (17) Scholar take important step toward understanding activated by various nitrogen-containing compounds that small Rho-like key intermediary between sensing activation. recent years, molecular picture regulation begun emerge, based studies model plant Arabidopsis Similar growth, part activating translation through phosphorylation S6K1, E2F transcription factors. addition, factors are targets regulation, EIN2 ethylene pathway (Fu 2021Fu Qin G. Wu P. Zi H. Xu Z. Yang S. al.The TOR-EIN2 axis mediates nuclear modulate growth.Nature. 591: 288-292Crossref (18) BZR1 brassinosteroid (Zhang 2016Zhang Zhu J.Y. Roh Marchive C. Kim S.K. Meyer Sun Z.Y. Signaling Promotes Accumulation Balance Carbon Availability Arabidopsis.Curr. 2016; 26: 1854-1860Abstract (115) receptors abscisic acid Proteomic have identified large number potential components network both evolutionarily plant-specific (Van Leene 2019Van Han Gadeyne A. Eeckhout D. Matthijs Cannoot B. De Winne N. Persiau Van Slijke E. de Cotte al.Capturing interaction landscape kinase.Nat. Plants. 5: 316-327Crossref (86) Plant sugar (Xiong 2013Xiong McCormack M. Hall Q. Xiang Glucose-TOR reprograms transcriptome activates meristems.Nature. 2013; 496: 181-186Crossref (405) auxin (Li 2017Li Cai T. Differential root shoot apexes.Proc. Natl. Acad. Sci. USA. 2017; 114: 2765-2770Crossref (133) well sulfur-containing precursors cysteine biosynthesis, phosphorous, (Cao 2019Cao S.J. Xing Schenck C.A. Jiang Last R.L. Brandizzi F. Homeostasis branched-chain critical activity Arabidopsis.eLife. 8: e50747Crossref (30) Scholar; While many activation, corresponding remain To understand regulated Arabidopsis, focused emergence first pair true leaves, transition marks onset photoautotrophic This process driven specialized region, meristem, located at apex. Regulation meristem interplay nutrients, hormonal signaling, playing Seedlings germinated absence could grow while, powered carbon reserves stored seed then encountered reversible arrest before emergence. When was added back, cycle primordium reactivated, measured increased Cyclin B1;1 promoter activity, leading development new leaves. substrate closely tracked concentration shoot, falling depleted rising rapidly again after resupply. Importantly, completely blocked when together Torin2, specific inhibitor TOR, demonstrating active necessary induction response nitrogen. By applying different combination inhibitors preventing their interconversion, authors further showed nitrate ammonium, sources, glutamine were potent TOR-activating compounds. The kinetics S6K1 rapid, plateauing within 30 min addition all three systematically tested 20 found 15 them varying degrees. noted most early products assimilation pathways (glutamine) sulfur (cysteine) or glycolate (glycine). Interestingly, these only partially overlap those animals differences correlate somewhat routes metabolism, suggesting evolutionary adaptation nitrogen-TOR pathways. How does TOR? Previous acts GTPase, downstream light perception, (Schepetilnikov 2017Schepetilnikov Makarian Srour O. Geldreich Chicher Hammann Ryabova L.A. binds target rapamycin, auxin.EMBO 36: 886-903Crossref (83) show nitrate, ammonia, glutamine. Auxin did not nitrogen-starved act auxin. Further, constitutively (GTP-bound) form apex, auxin, may converge TOR. distinct GTPases mediate acid-TOR similarities two kingdoms mechanisms intriguing (Figure 1). diverse (nitrate, acids) unknown plants. rapid effects (S6K1 detected 5 min) suggest direct signaling. several absent well-characterized receptor NRT1.1 dispensable nitrate-TOR (Liu Further research will be uncover sensors channel integrator Plants prioritize allocation limited development. Here, shortage arrests increases uptake Such opposite responses higher levels acids, TOR-activity than under nitrogen-limiting condition. contrast, sugar-limiting conditions, inactivated roots (a sink tissue sugar) These findings indicate functions switch maintain homeostasis carbon- nitrogen-related processes aboveground underground tissues. Therefore, coordinate transport/allocation metabolism improving use efficiency crop productivity. declare no competing interests. Z.-Y.W. professor courtesy Stanford University. ArabidopsisLiu al.Developmental CellApril 7, 2021In BriefAmino (AAs) mammalian Autotrophic absorb convert into AAs. reveal AAs function separate stimulate independent nitrogen-assimilation pathway. Full-Text