Differential TOR activation and cell proliferation in Arabidopsis root and shoot apexes

Growth and cell proliferation at the shoot and root apexes are regulated by diverse factors including hormones, nutrients, and light. Previously, the protein kinase TOR (Target of Rapamycin), a transducer of glucose energy signals, was shown to phosphorylate and activate the transcription factor E2Fa, an activator of S-phase genes and cell division, in the root meristem. Li et al. show that TOR similarly transduces the glucose signal in the shoot meristem, but that TOR activation and shoot meristem activation also requires light signals. They further showed that auxin could substitute for light signals in the activation of TOR. Together, these studies show that while glucose is sufficient to promote root meristem activity, light/auxin is additionally required in the shoot. Proc. Natl. Acad. Sci. USA