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United States Department of Agriculture

Agricultural Research Service

Title: Out of the dark: how the PIFs are unmasking a dual temporal mechanism of phytochrome signalling)

Author
item Monte, Elena
item Al-sady, Bassem
item Leivar, Pablo
item Quail, Peter

Submitted to: Journal of Experimental Biology Online
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2007
Publication Date: 9/12/2007
Publication URL: http://jxb.oxfordjournals.org/cgi/reprint/58/12/3125
Citation: Monte, E., Al-Sady, B., Leivar, P., Quail, P. 2007. Out of the dark: how the PIFs are unmasking a dual temporal mechanism of phytochrome signalling. Journal of Experimental Biology. 3(58):3125-3133.

Interpretive Summary: Following light-induced nuclear translocation, the phytochromes induce changes in gene expression to regulate plant development. PIF3 and other PIFs (phytochrome-interacting factors), members of the bHLH (basic helix–loop–helix) family of transcriptional regulators, interact specifically with the active Pfr conformer of the phytochrome molecule, suggesting that the PIFs are key components of phytochrome signal transduction. The mechanism by which the PIFs transduce phytochrome signals is not understood. After initial studies that suggested that PIF3 was a positive regulator of phytochrome signalling, mutant studies indicated that the PIFs primarily act as negative regulators in the pathway. Furthermore, in some cases they accumulate in the dark and are degraded upon illumination by the ubiquitin–26S proteasome system. At least for PIF3, the protein degradation depends on direct interaction with the phytochrome molecule and is preceded by protein phosphorylation. In this review, the current understanding of the role of the PIFs in phytochrome-mediated photomorphogenesis will be summarized, and recent findings suggesting an unanticipated dual mechanism of action of the PIFs will be discussed.

Technical Abstract: Following light-induced nuclear translocation, the phytochromes induce changes in gene expression to regulate plant development. PIF3 and other PIFs (phytochrome-interacting factors), members of the bHLH (basic helix–loop–helix) family of transcriptional regulators, interact specifically with the active Pfr conformer of the phytochrome molecule, suggesting that the PIFs are key components of phytochrome signal transduction. The mechanism by which the PIFs transduce phytochrome signals is not understood. After initial studies that suggested that PIF3 was a positive regulator of phytochrome signalling, mutant studies indicated that the PIFs primarily act as negative regulators in the pathway. Furthermore, in some cases they accumulate in the dark and are degraded upon illumination by the ubiquitin–26S proteasome system. At least for PIF3, the protein degradation depends on direct interaction with the phytochrome molecule and is preceded by protein phosphorylation. In this review, the current understanding of the role of the PIFs in phytochrome-mediated photomorphogenesis will be summarized, and recent findings suggesting an unanticipated dual mechanism of action of the PIFs will be discussed.

Last Modified: 8/24/2016
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