TOR tour to auxin

Abstract

EMBO J (2013) 32: 1087–1102 doi:; DOI: 10.1038/emboj.2013.61; published online March 22 2013

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.

Figure 1

Regulation of cell growth and proliferation by the growth hormone, auxin, and nutrients. (A) Auxin (A) canonical signalling components are labelled red. Auxin has a two-receptor system for its signal transduction, and these as well as nutrient signalling might converge through TOR that regulates the selective translation of ARFs. For details, see text. (B) Plant growth is very plastic and adaptable to changing environmental conditions. A long known example is gravitropic growth of, for example, roots that is regulated by differential auxin distribution from the root cap in epidermal layers; auxin is being depleted in the upper face. This leads to a curvature that relies primarily on selective cell enlargement and in longer terms also on cell proliferation. Schepetilnikov et al (2013) show that TOR is involved in this process. (C) TOR integrates auxin and nutrient signalling primarily by regulated protein translation. Selective protein translation of key transcriptional regulators could sensitise the second auxin perception system within the nucleus to regulate auxin-responsive transcription. Protein translation underpins growth that drives cell proliferation. However, growth can also repress proliferation to allow cells to attain larger sizes in nutrient-rich condition, and proliferation can repress growth to maintain cells in a meristematic state.