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Review
. 2018 Jan;217(2):547-551.
doi: 10.1111/nph.14886. Epub 2017 Nov 15.

New Insights Into the Mechanisms of Phytochrome-Cryptochrome Coaction

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Free PMC article
Review

New Insights Into the Mechanisms of Phytochrome-Cryptochrome Coaction

Qin Wang et al. New Phytol. .
Free PMC article

Abstract

Contents Summary 547 I. Introduction 547 II. Phytochromes mediate light-induced transcription of BICs to inactivate cryptochromes 548 III. PPKs phosphorylate light-signaling proteins and histones to affect plant development 548 IV. Prospect 550 Acknowledgements 550 References 550 SUMMARY: Plants perceive and respond to light signals by multiple sensory photoreceptors, including phytochromes and cryptochromes, which absorb different wavelengths of light to regulate genome expression and plant development. Photophysiological analyses have long revealed the coordinated actions of different photoreceptors, a phenomenon referred to as the photoreceptor coaction. The mechanistic explanations of photoreceptor coactions are not fully understood. The function of direct protein-protein interaction of phytochromes and cryptochromes and common signaling molecules of these photoreceptors, such as SPA1/COP1 E3 ubiquitin ligase complex and bHLH transcription factors PIFs, would partially explain phytochrome-cryptochrome coactions. In addition, newly discovered proteins that block cryptochrome photodimerization or catalyze cryptochrome phosphorylation may also participate in the phytochrome and cryptochrome coaction. This Tansley insight, which is not intended to make a comprehensive review of the studies of photoreceptor coactions, attempts to highlight those recent findings and their possible roles in the photoreceptor coaction.

Keywords: Blue-light Inhibitors of Cryptochrome1 (BIC1); Photoregulatory Protein Kinase1 (PPK1); blue light; cryptochromes; phytochromes.

Figures

Fig. 1
Fig. 1
Phytochromes (PHY) mediate light-induced transcription of Bluelight Inhibitors of Cryptochromes (BICs) to inactivate cryptochromes. This model depicts that CRY2 undergoes photodimerization to become active. The active CRY2 inhibits SPA/COP1 ubiquitin ligase activity, leading to increased activity of the HY5 transcription factor, and accumulation of BIC proteins that inhibits CRY2 photodimerization. Phytochromes also activate BIC expression to suppress CRY2 photodimerization and photoactivation. Solid arrows or T-bar indicate positive or negative actions, respectively, dotted arrow indicates translation. Pr, Pr form of PHY; Pfr, Pfr form of PHY.
Fig. 2
Fig. 2
Potential roles of photoregulatory protein kinases (PPKs) in phytochrome–cryptochrome coactions. This model depicts that PPKs phosphorylate CRY2 and PIF3, resulting in degradation of CRY2, PIF3 and phyB. PPKs also phosphorylate histones H3 and H2A, which may affect phytochrome- and cryptochrome-dependent chromatin remodeling and plant development. Pi, phosphorylation; EC, evening complex; PHY, phyA, B, C, D, E, E3X,COP1and unknownE3 ubiquitin ligases; LRB, Light Response Bric-a-Brack/Tramtrack/Broad (BTB) E3 ubiquitin ligase. Solid or dotted arrows indicate positive actions possibly by multiple steps.

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