The TOR-EIN2 axis mediates nuclear signalling to modulate plant growth

The evolutionarily conserved target of rapamycin (TOR) kinase acts as a master regulator that coordinates cell proliferation and growth by integrating nutrient, energy, hormone and stress signals in all eukaryotes.sup.1,2. Research has focused mainly on TOR-regulated translation, but how TOR orchestrates the global transcriptional network remains unclear. Here we identify ethylene-insensitive protein 2 (EIN2), a central integrator.sup.3-5 that shuttles between the cytoplasm and the nucleus, as a direct substrate of TOR in Arabidopsis thaliana. Glucose-activated TOR kinase directly phosphorylates EIN2 to prevent its nuclear localization. Notably, the rapid global transcriptional reprogramming that is directed by glucose-TOR signalling is largely compromised in the ein2-5 mutant, and EIN2 negatively regulates the expression of a wide range of target genes of glucose-activated TOR that are involved in DNA replication, cell wall and lipid synthesis and various secondary metabolic pathways. Chemical, cellular and genetic analyses reveal that cell elongation and proliferation processes that are controlled by the glucose-TOR-EIN2 axis are decoupled from canonical ethylene-CTR1-EIN2 signalling, and mediated by different phosphorylation sites. Our findings reveal a molecular mechanism by which a central signalling hub is shared but differentially modulated by diverse signalling pathways using distinct phosphorylation codes that can be specified by upstream protein kinases. In Arabidopsis, phosphorylation of EIN2 by TOR kinase in the presence of glucose prevents the nuclear localization of EIN2, showing that the glucose-TOR-EIN2 axis regulates the transcriptome independently of ethylene signalling pathways.
Author(s): Liwen Fu [sup.1] [sup.2] , Yanlin Liu [sup.2] , Guochen Qin [sup.1] , Ping Wu [sup.3] , Hailing Zi [sup.1] , Zhongtian Xu [sup.1] , Xiaodi Zhao [sup.2] , [...]