A mutually assured destruction mechanism attenuates light signaling in Arabidopsis

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Science  06 Jun 2014:
Vol. 344, Issue 6188, pp. 1160-1164
DOI: 10.1126/science.1250778

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Emerging from the shade into the light

As a growing seedling emerges into the light, it needs to shift its developmental program to grow toward the light. Signaling components that flip the switch from growth in the shade to growth in the light include phytochromes, which are sensitive to red light, and transcription factors that drive the shade-adapted pattern of development. Ni et al. now show how phosphorylation sets these signaling partners up for destruction. The signaling established by red light invokes photomorphogenesis by promoting the destruction of the photoreceptor and its signaling partner.

Science, this issue p. 1160


After light-induced nuclear translocation, phytochrome photoreceptors interact with and induce rapid phosphorylation and degradation of basic helix-loop-helix transcription factors, such as PHYTOCHROME-INTERACTING FACTOR 3 (PIF3), to regulate gene expression. Concomitantly, this interaction triggers feedback reduction of phytochrome B (phyB) levels. Light-induced phosphorylation of PIF3 is necessary for the degradation of both proteins. We report that this PIF3 phosphorylation induces, and is necessary for, recruitment of LRB [Light-Response Bric-a-Brack/Tramtrack/Broad (BTB)] E3 ubiquitin ligases to the PIF3-phyB complex. The recruited LRBs promote concurrent polyubiqutination and degradation of both PIF3 and phyB in vivo. These data reveal a linked signal-transmission and attenuation mechanism involving mutually assured destruction of the receptor and its immediate signaling partner.

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