PIF4 and PIF5 Transcription Factors Link Blue Light and Auxin to Regulate the Phototropic Response in Arabidopsis

Abstract

Both blue light (BL) and auxin are essential for phototropism in Arabidopsis thaliana. However, the mechanisms by which light is molecularly linked to auxin during phototropism remain elusive. Here, we report that PHYTOCHROME INTERACTING FACTOR4 (PIF4) and PIF5 act downstream of the BL sensor PHOTOTROPIN1 (PHOT1) to negatively modulate phototropism in Arabidopsis. We also reveal that PIF4 and PIF5 negatively regulate auxin signaling. Furthermore, we demonstrate that PIF4 directly activates the expression of the AUXIN/INDOLE-3-ACETIC ACID (IAA) genes IAA19 and IAA29 by binding to the G-box (CACGTG) motifs in their promoters. Our genetic assays demonstrate that IAA19 and IAA29, which physically interact with AUXIN RESPONSE FACTOR7 (ARF7), are sufficient for PIF4 to negatively regulate auxin signaling and phototropism. This study identifies a key step of phototropic signaling in Arabidopsis by showing that PIF4 and PIF5 link light and auxin.

PIF4-controlled auxin pathway contributes to hybrid vigor in Arabidopsis thaliana

“…Overexpression of PIF4 doubles the expression level of YUC8 and elevates endogenous-free IAA levels to 50% above wild type (19). The expression of IAA29 was increased in a 35S-PIF4 overexpression line, and decreased in the pif4 pif5 double mutant compared with the wild type (20). In our experiments, PIF4 was up-regulated in the F1 hybrids and the three hybrid mimics and down-regulated in the small line (Sml-D) (Fig.…”

“…YUC8 and IAA29 are activated by the transcription factor PIF4 (19,20). The expression of the auxin biosynthesis genes TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1 (TAA1) and YUC8 can be induced by transzeatin treatment in wild-type plants, but not in a pif4 mutant, indicating PIF4 is required for cytokinin-dependent auxin biosynthesis, which leads to cell division (22).…”

PIFs: Systems Integrators in Plant Development

“…Intriguingly, although PIFq members have been shown to inhibit seedling photomorphogenic development in blue light (Kang and Ni, 2006;Castillon et al, 2009;Kunihiro et al, 2010;Bu et al, 2011a), this effect appears to be mediated by phy, at least in the case of PIF1 and possibly PIF3 (Castillon et al, 2009;Bu et al, 2011a). By contrast, PIF4 and PIF5 have been shown to repress phototropism downstream of the blue light sensor phototropin (Sun et al, 2013).…”

“…In turn, PIFs are also proposed to regulate auxin signaling by inducing the expression of several AUX/IAA and SAUR genes during deetiolation, shade, diurnal growth, and high-temperature responses (Franklin et al, 2011;Nozue et al, 2011;Hornitschek et al, 2012;Leivar et al, 2012b;Li et al, 2012). Interestingly, IAA19 and IAA29 (Sun et al, 2013), as well as SAUR19 (Franklin et al, 2011), are shown to participate in phototropic and high-temperature responses, respectively, downstream of the PIFs. During hook formation, PIFs regulate auxin transport by directly inducing WAG2 (Willige et al, 2012) and ethylene levels by directly inducing ACS5 and ACS8 expression Gallego-Bartolomé et al, 2011).…”

Gene expression profile of <i>Arabidopsis</i> plants that overexpress <i>ZEITLUPE/LOV KELCH PROTEIN1</i>: up-regulation of auxin-inducible genes in hypocotyls

“…PIF4 is a basic helix-loop-helix transcription factor that promotes hypocotyl elongation by activating the expression of genes involved in auxin biosynthesis, auxin signaling components, cell wall loosening, and cell expansion (Hornitschek et al 2012;Leivar and Quail 2011;de Lucas and Prat 2014;Sun et al 2013). Therefore, the up-regulation of PIF4 might lead to elevation of auxin biosynthesis and up-regulation of SAURs in ZTLoverexpressing seedlings.…”