TOR tour to auxin

Abstract

Auxin is a principal growth hormone in plants. A study by Schepetilnikov et al (2013) now reports that TOR is activated by auxin and regulates expression of auxin‐responsive genes by facilitating translation reinitiation of mRNAs with uORFs at their 5′ UTRs. In this way, TOR acts at the crossroad of the plasma membrane and nuclear auxin signalling pathways to link auxin with general nutrient signalling. Auxin signalling acts through concentration gradients to regulate developmental processes in plants and the flow of Auxin can be rapidly altered by environmental stimuli resulting in the redirection of plant growth. Auxin concentrations are read and translated into gradients of regulatory proteins, as seen for the PLETHORA (PLT) transcription factors, which determine cellular states, such as stem cell maintenance, cell proliferation, and cell elongation. The currently dominating view is that auxin is perceived by the nuclear TIR/AFB receptors, F‐box proteins, which regulate turnover of the AUX/IAA transcriptional repressors to control gene transcription through a family of AUXIN RESPONSE FACTORs (ARFs; Figure 1; Hayashi, 2012). Schepetilnikov et al (2013) now show that auxin also controls the abundance of key regulators in a post‐transcriptional manner involving selective protein translation. They report that auxin activates TARGET OF RAPAMICIN (TOR), the evolutionary conserved central growth regulator in yeast, plants, and animals. TOR is known to control protein translation through translation initiation in yeast and animals, but its role is less well understood in plants. It was previously …