Phytochrome interacting factors 4 and 5 control seedling growth in changing light conditions by directly controlling auxin signaling

Abstract

SUMMARYPlant growth is strongly influenced by the presence of neighbors that compete for light resources. In response to vegetational shading shade-intolerant plants such as Arabidopsis display a suite of developmental responses known as the shade-avoidance syndrome (SAS). The phytochrome B (phyB) photoreceptor is the major light sensor to mediate this adaptive response. Control of the SAS occurs in part with phyB, which controls protein abundance of phytochrome-interacting factors 4 and 5 (PIF4 and PIF5) directly. The shadeavoidance response also requires rapid biosynthesis of auxin and its transport to promote elongation growth. The identification of genome-wide PIF5-binding sites during shade avoidance revealed that this bHLH transcription factor regulates the expression of a subset of previously identified SAS genes. Moreover our study suggests that PIF4 and PIF5 regulate elongation growth by controlling directly the expression of genes that code for auxin biosynthesis and auxin signaling components.

PIFs: Systems Integrators in Plant Development

“…Recent studies under high R/FR conditions show that PIFq members also promote hypocotyl elongation in response to a reduction in PAR (Hornitschek et al, 2012;Leivar et al, 2012a), suggesting that PIFs exert integration of low R/FR and low PAR signals. Low PAR conditions involve a reduction in both R and blue light, so future examination is required to determine whether this role of PIFs in promoting growth in low PAR is due to a reduction in phyB signaling and/or a reduction in signaling via the blue light-sensing cryptochrome (cry) receptor.…”

“…RNA-seq studies allow the identification of PIFq-regulated genes with full genome coverage, such as the identification of 2025 genes that are misregulated in the pifq mutant in the dark (Zhang et al, 2013), nearly twice the number of genes identified by microarray analysis under equivalent growth conditions (Leivar et al, 2009). ChIP-seq technology has been used to define the genomic occupancy of PIF3 (Zhang et al, 2013) and PIF4 in etiolated seedlings and of PIF5 in shade (Hornitschek et al, 2012) (see below). These studies have defined high confidence binding sites in the genome for each of these PIFs and the associated genes, including 828 genes for PIF3, 4363 genes for PIF4, and 1218 genes for PIF5.…”

Phytochromes and Phytochrome Interacting Factors

“…In vitro gel-shift, random DNA-binding selection, and in vivo chromatin immunoprecipitation (ChIP) assays show that four major PIFs (PIF1, PIF3, PIF4, and PIF5) bound to either the G-box (CACGTG) and/or the E box (CANNTG), which are called PIF-binding E boxes (Martínez-Garcia et al, 2000;Huq and Quail, 2002;Huq et al, 2004;Hornitschek et al, 2012). A number of proteins that interact directly with PIFs modulate the DNA binding and, consequently, the transcriptional activity of PIFs ( Fig.…”

Photobody Localization of Phytochrome B Is Tightly Correlated with Prolonged and Light-Dependent Inhibition of Hypocotyl Elongation in the Dark

“…Next, to assess the transcriptional activity of PIF3 in the PBG and NGB lines at various time points during the R-to-D transition, we determined the expression levels of four wellcharacterizedPIFtargetgenes:PHYTOCHROME-INTERACTING FACTOR3-Like1 (PIL1), INDOLE-3-ACETIC ACID INDUCIBLE29 (IAA29), XYLOGLUCAN EDOTRANSGLYCOSYLASE7 (XTR7), and ARABIDOPSIS THALIANA HOMEOBOX PROTEIN2 (ATHB2) (Leivar et al, 2009(Leivar et al, , 2012bHornitschek et al, 2012). None of these genes were activated in pifq (Fig.…”