Genetically encodable optical reporters, such as green fluorescent protein, have revolutionized the observation and measurement of cellular states. However, the inverse challenge of using light to control precisely cellular behaviour has only recently begun to be addressed; semi-synthetic chromophore-tethered receptors and naturally occurring channel rhodopsins have been used to perturb directly neuronal networks. The difficulty of engineering light-sensitive proteins remains a significant impediment to the optical control of most cell-biological processes. Here we demonstrate the use of a new genetically encoded light-control system based on an optimized, reversible protein-protein interaction from the phytochrome signalling network of Arabidopsis thaliana. Because protein-protein interactions are one of the most general currencies of cellular information, this system can, in principle, be generically used to control diverse functions. Here we show that this system can be used to translocate target proteins precisely and reversibly to the membrane with micrometre spatial resolution and at the second timescale. We show that light-gated translocation of the upstream activators of Rho-family GTPases, which control the actin cytoskeleton, can be used to precisely reshape and direct the cell morphology of mammalian cells. The light-gated protein-protein interaction that has been optimized here should be useful for the design of diverse light-programmable reagents, potentially enabling a new generation of perturbative, quantitative experiments in cell biology.

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Spatiotemporal control of cell signalling using a light-switchable protein interaction

https://www.cell.com/trends/plant-science/pdf/S1360-1385(10)00162-7.pdf

PIFs: pivotal components in a cellular signaling hub

Integration of Brassinosteroid Signal Transduction with the Transcription Network for Plant Growth Regulation in Arabidopsis

Plant hormones are small molecules that regulate plant growth and development, as well as responses to changing environmental conditions. By modifying the production, distribution or signal transduction of these hormones, plants are able to regulate and coordinate both growth and/or stress tolerance to promote survival or escape from environmental stress. A central role for the gibberellin (GA) class of growth hormones in the response to abiotic stress is becoming increasingly evident. Reduction of GA levels and signalling has been shown to contribute to plant growth restriction on exposure to several stresses, including cold, salt and osmotic stress. Conversely, increased GA biosynthesis and signalling promote growth in plant escape responses to shading and submergence. In several cases, GA signalling has also been linked to stress tolerance. The transcriptional regulation of GA metabolism appears to be a major point of regulation of the GA pathway, while emerging evidence for interaction of the GA-signalling molecule DELLA with components of the signalling pathway for the stress hormone jasmonic acid suggests additional mechanisms by which GA signalling may integrate multiple hormone signalling pathways in the response to stress. Here, we review the evidence for the role of GA in these processes, and the regulation of the GA signalling pathway on exposure to abiotic stress. The potential mechanisms by which GA signalling modulates stress tolerance are also discussed.

/pdf/the-role-of-gibberellin-signalling-in-plant-responses-to-9wuqxdfvgf.pdf

The role of gibberellin signalling in plant responses to abiotic stress

Plant growth and development are particularly sensitive to changes in the light environment and especially to vegetational shading. The shade-avoidance response is mainly controlled by the phytochrome photoreceptors. In Arabidopsis, recent studies have identified several related bHLH class transcription factors (PIF, for phytochrome-interacting factors) as important components in phytochrome signaling. In addition to a related bHLH domain, most of the PIFs contain an active phytochrome binding (APB) domain that mediates their interaction with light-activated phytochrome B (phyB). Here we show that PIF4 and PIF5 act early in the phytochrome signaling pathways to promote the shade-avoidance response. PIF4 and PIF5 accumulate to high levels in the dark, are selectively degraded in response to red light, and remain at high levels under shade-mimicking conditions. Degradation of these transcription factors is preceded by phosphorylation, requires the APB domain and is sensitive to inhibitors of the proteasome, suggesting that PIF4 and PIF5 are degraded upon interaction with light-activated phyB. Our data suggest that, in dense vegetation, which is rich in far-red light, shade avoidance is triggered, at least partially, as a consequence of reduced phytochrome-mediated degradation of transcription factors such as PIF4 and PIF5. Consistent with this idea, the constitutive shade-avoidance phenotype of phyB mutants partially reverts in the absence of PIF4 and PIF5.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.2007.03341.x

Phytochrome-mediated inhibition of shade avoidance involves degradation of growth-promoting bHLH transcription factors

Phytochromes are a widespread family of red/far-red responsive photoreceptors first discovered in plants, where they constitute one of the three main classes of photomorphogenesis regulators. All phytochromes utilize covalently attached bilin chromophores that enable photoconversion between red-absorbing (Pr) and far-red-absorbing (Pfr) forms. Phytochromes are thus photoswitchable photosensors; canonical phytochromes have a conserved N-terminal photosensory core and a C-terminal regulatory region, which typically includes a histidine-kinase-related domain. The discovery of new bacterial and cyanobacterial members of the phytochrome family within the last decade has greatly aided biochemical and structural characterization of this family, with the first crystal structure of a bacteriophytochrome photosensory core appearing in 2005. This structure and other recent biochemical studies have provided exciting new insights into the structure of phytochrome, the photoconversion process that is central to...

/pdf/phytochrome-structure-and-signaling-mechanisms-bwi9ybrw78.pdf

Phytochrome structure and signaling mechanisms

The photoreversibility of plant phytochromes enables continuous surveillance of the ambient light environment. Through expression of profluorescent, photoinsensitive Tyr-to-His mutant alleles of Arabidopsis thaliana phytochrome B (PHYB(Y276H)) and Arabidopsis phytochrome A (PHYA(Y242H)) in transgenic Arabidopsis plants, we demonstrate that photoconversion is not a prerequisite for phytochrome signaling. PHYB(Y276H)-expressing plants exhibit chromophore-dependent constitutive photomorphogenesis, light-independent phyB(Y276H) nuclear localization, constitutive activation of genes normally repressed in darkness, and light-insensitive seed germination. Fluence rate analyses of transgenic plants expressing PHYB(Y276H), PHYA(Y242H), and other Y(GAF) mutant alleles of PHYB demonstrate that a range of altered light-signaling activities are associated with mutation of this residue. We conclude that the universally conserved GAF domain Tyr residue, with which the bilin chromophore is intimately associated, performs a critical role in coupling light perception to signal transduction by plant phytochromes.

/pdf/light-independent-phytochrome-signaling-mediated-by-dominant-m0npqw4ysu.pdf

Light-Independent Phytochrome Signaling Mediated by Dominant GAF Domain Tyrosine Mutants of Arabidopsis Phytochromes in Transgenic Plants

A light-independent allele of phytochrome B faithfully recapitulates photomorphogenic transcriptional networks.

This invention pertains to the discovery of mutant phytochromes that when introduced into a plant alter the photomorphogenic properties of that plant. In certain embodiments transfection of plants by nucleic acid constructs expressing the mutant phytochromes produced plants having a phenotype characterized by light-independent' activation. Thus, in certain embodiments, this invention provides a transgenic plant or plant cell comprising a mutant phytochrome where the mutant phytochrome is a light-stable phytochrome; and the transgenic plant shows decreased shade avoidance as compared to the same species or strain of plant lacking the mutant phytochrome. In various embodiments the mutant phytochrome comprises a mutation at the position corresponding to tyrosine residue 276 in an Arabidopsis phytochrome where the mutation is to a residue other than tyrosine.

Yi-Shin Su

Papers

Phytochrome structure and signaling mechanisms

Light-Independent Phytochrome Signaling Mediated by Dominant GAF Domain Tyrosine Mutants of Arabidopsis Phytochromes in Transgenic Plants

A light-independent allele of phytochrome B faithfully recapitulates photomorphogenic transcriptional networks.

Transgenic plants comprising a mutant phytochrome and showing altered photomorphogenesis