Rewiring of auxin signaling under persistent shade

PUCCIARELLO, O; LEGRIS, M; COSTIGLIOLO ROJAS C; IGLESIAS, MJ; HERNANDO, CE; DEZAR, C; VAZQUEZ, M; YANOVSKY, MJ; FINLAYSON, SA; PRAT, S; CASAL, JJ

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA

NATL ACAD SCIENCES

Lugar: Washington DC, USA; Año: 2018 vol. 115 p. 5612 - 5617

0027-8424

Light cues from neighboring vegetation rapidly initiate plantshade-avoidance responses. Despite our detailed knowledge ofthe early steps of this response, the molecular events underprolonged shade are largely unclear. Here we show that persistentneighbor cues reinforce growth responses in addition to promoting auxin-responsive gene expression in Arabidopsis and soybean. However, while the elevation of auxin levels is wellestablished as an early event, in Arabidopsis, the response to prolonged shade occurs when auxin levels have declined to the prestimulation values. Remarkably, the sustained low activity ofphytochrome B under prolonged shade led to (i) decreased levelsof PHYTOCHROME INTERACTING FACTOR 4 (PIF4) in the cotyledons (the organs that supply auxin) along with increased levelsin the vascular tissues of the stem, (ii) elevated expression of thePIF4 targets INDOLE-3-ACETIC ACID 19 (IAA19) and IAA29, which inturn reduced the expression of the growth-repressive IAA17 regulator, (iii) reduced abundance of AUXIN RESPONSE FACTOR 6, (iv)reduced expression of MIR393 and increased abundance of its targets, the auxin receptors, and (v) elevated auxin signaling as indicated by molecular markers. Mathematical and genetic analysessupport the physiological role of this system-level rearrangement.We propose that prolonged shade rewires the connectivity between light and auxin signaling to sustain shade avoidance without enhanced auxin levels.