Arabidopsis TOR signaling is essential for sugar-regulated callus formation.

Dedifferentiation is a remarkable process that produces pluripotent stem cells from differentiated somatic cells to ensure developmental plasticity. Plants have evolved the ability of cellular dedifferentiation, and signaling cascades related to auxin and cytokinin-dependent callus formation have been extensively investigated. However, the molecular mechanism underlying sugar-dependent callus formation remains unknown. Here, we show that sugar-dependent callus formation is mainly regulated by the TOR-E2Fa module in Arabidopsis. Sugar-activated TOR kinase phosphorylates and stabilizes E2Fa proteins to transcriptionally activate S-phase genes during callus formation. In parallel, E2Fa is transcriptionally regulated by the ARF-LBD transcription cascade. Multi-layered regulation of E2Fa by sugar and auxin is likely to shape balanced cellular dedifferentiation capability in Arabidopsis.