The phytohormone auxin induces or represses growth depending on its concentration and the underlying tissue type. However, it remains unknown how auxin signalling is modulated to allow tissues transiting between repression and promotion of growth. Here, we used apical hook development as a model for growth transitions in plants. A PIN-FORMED (PIN)-dependent intercellular auxin transport module defines an auxin maximum that is causal for growth repression during the formation of the apical hook. Our data illustrate that growth transition for apical hook opening is largely independent of this PIN module, but requires the PIN-LIKES (PILS) putative auxin carriers at the endoplasmic reticulum. PILS proteins reduce nuclear auxin signalling in the apical hook, leading to the de-repression of growth and the onset of hook opening. We also show that the phytochrome (phy) B-reliant light-signalling pathway directly regulates PILS gene activity, thereby enabling light perception to repress nuclear auxin signalling and to control growth. We propose a novel mechanism, in which PILS proteins allow external signals to alter tissue sensitivity to auxin, defining differential growth rates.
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We are grateful to P. Zadnikova and E. Benkova for introducing us to infrared-based time lapse imaging; D. Scheuring and F. Barbez for helping us establishing our infrared imaging station; C. Fankhauser, P. Wigge, J. Friml and A. Maizel for providing published material; E. Benkova, M. Geisler, U. Hammes and J.K.-V. group members for critical reading of the manuscript; J. Thacker for help with the manuscript; and the BOKU-VIBT Imaging Centre for access and expertise. This work was supported by the Vienna Research Group (VRG) programme of the Vienna Science and Technology Fund (WWTF), the Austrian Science Fund (FWF) (Projects: P26568-B16 and P26591-B16) and the European Research Council (ERC) (Starting Grant 639478-AuxinER) (to J.K.-V.) as well as the APART fellowship of the Austrian Academy of Sciences (ÖAW) (to D.L.).
The authors declare no competing financial interests.
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Béziat, C., Barbez, E., Feraru, M. et al. Light triggers PILS-dependent reduction in nuclear auxin signalling for growth transition. Nature Plants 3, 17105 (2017). https://doi.org/10.1038/nplants.2017.105