Expanding Roles of PIFs in Signal Integration from Multiple Processes

Abstract

PHYTOCHROME INTERACTING FACTORs (PIFs) are members of the basic helix-loop-helix (bHLH) family of transcription factors in Arabidopsis. Since their discovery in phytochrome-mediated light signaling pathways, recent studies have unraveled new functions of PIFs in integrating multiple signaling pathways not only by their role as transcription factors directly targeting gene expression, but also by interacting with diverse groups of factors to optimize plant growth and development. These include endogenous (e.g., hormonal) as well as abiotic (light, circadian and elevated temperature) and biotic (defense responses) pathways. PIFs interact with key factors in each of these pathways, and tailor the outcome of the signal integration among these pathways. This review summarizes the role of PIFs as pivotal signal integrators in regulating plant growth and development.

Phytochromes and Phytochrome Interacting Factors

“…Thus, having multiple kinases and E3 ubiquitin ligases might allow fine-tuning the rate of degradation and the sensitivity to different fluences. Second, PIFs are not involved only in light signaling pathways, but recent studies highlight the importance of PIFs in multiple aspects of plant growth and development and response pathways (Leivar and Monte, 2014;Paik et al, 2017). Thus, PIFs act as a central hub in many cellular signaling pathways (e.g.…”

“…Thus, PIFs act as a central hub in many cellular signaling pathways (e.g. GA, brassinosteroid [BR], auxin, ethylene, JA, circadian, and many others; Leivar and Monte, 2014;Paik et al, 2017). Therefore, signaling factors from these pathways (e.g.…”

“…A number of proteins that interact directly with PIFs modulate the DNA binding and, consequently, the transcriptional activity of PIFs ( Fig. 4; Paik et al, 2017). These are divided into two classes: factors enhancing PIF DNA-binding activity (Fig.…”

“…Finally, we discuss the dynamic regulation of PIF DNA-binding and transcriptional activities through PIF-interacting partners. For details on the roles of phytochromes and PIFs in other pathways, readers are directed to recently published review articles (Legris et al, 2017;Paik et al, 2017).…”

Light Signaling, Root Development, and Plasticity

“…The PHY and CRY photoreceptors can physically interact with specific sets of PIF proteins and thereby regulate PIF phosphorylation. The phosphorylation status of PIFs subsequently determines their activity and in most instances their stability (Paik et al, 2017). ChIP-seq studies on PIFs have identified a very broad range of target genes, including those associated with cell wall modifications, auxin biology and several other transcription factors.…”