Phototropin (phot) is a blue light (BL) receptor and thermosensor that mediates chloroplast movements in plants. Liverworts, as early‐diverging plant species, have a single copy of PHOT gene, and the ...phot protein in each liverwort activates the signaling pathway adapted to its specific growing environment. In this study, we functionally compared phot from two different liverworts species: Apopellia endiviifolia (Aephot) and Marchantia polymorpha (Mpphot). The BL‐dependent photochemical activity of Aephot was similar to that of Mpphot, whereas the thermochemical activity of Aephot was lower than that of Mpphot. Therefore, the phot‐mediated signaling pathways of the two plant species may differ more in response to temperature than to BL. Furthermore, we analyzed the functional compatibility of Aephot and Mpphot in chloroplast movements by transiently expressing AePHOT or MpPHOT. The transient expression of AePHOT did not mediate chloroplast movement in M. polymorpha, showing the incompatibility of Aephot with the signaling pathway of M. polymorpha. By contrast, the transient expression of MpPHOT mediated chloroplast movement in A. endiviifolia, indicating the compatibility of Mpphot with the signaling pathway of A. endiviifolia. Our findings reveal both functional similarities and differences between Aephot and Mpphot proteins from the closely related liverworts.
The phototropin (phot) of two closed liverworts species: Apopellia endiviifolia (Aephot) and Marchantia polymorpha (Mpphot) have been functionally compared in this study. Both Aephot and Mpphot show similarities in their photocycle, but diversity in the functions of regulating chloroplast movement. The transient expression of AePHOT did not mediate chloroplast movement in M. polymorpha, showing the incompatibility of Aephot with the signaling pathway of M. polymorpha. By contrast, the transient expression of MpPHOT‐mediated chloroplast movement in A. endiviifolia indicates the compatibility of Mpphot with the signaling pathway of A. endiviifolia.
Drought tolerance is important for grain crops, including rice (Oryza sativa); for example, rice cultivated under intermittent irrigation produces less methane gas compared to rice grown in anaerobic ...paddy field conditions, but these plants require greater drought tolerance. Moreover, the roles of rice circadian‐clock genes in drought tolerance remain largely unknown. Here, we show that the mutation of LOV KELCH REPEAT PROTEIN 2 (OsLKP2) enhanced drought tolerance by increasing cuticular wax biosynthesis. Among ZEITLUPE family genes, OsLKP2 expression specifically increased under dehydration stress. OsLKP2 knockdown (oslkp2‐1) and knockout (oslkp2‐2) mutants exhibited enhanced drought tolerance. Cuticular waxes inhibit non‐stomatal water loss. Under drought conditions, total wax loads on the leaf surface increased by approximately 10% in oslkp2‐1 and oslkp2‐2 compared to the wild type, and the transcript levels of cuticular wax biosynthesis genes were upregulated in the oslkp2 mutants. Yeast two‐hybrid, bimolecular fluorescence complementation, and coimmunoprecipitation assays revealed that OsLKP2 interacts with GIGANTEA (OsGI) in the nucleus. The osgi mutants also showed enhanced tolerance to drought stress, with a high density of wax crystals on their leaf surface. These results demonstrate that the OsLKP2‐OsGI interaction negatively regulates wax accumulation on leaf surfaces, thereby decreasing rice resilience to drought stress.
Summary statement
Loss of LOV KELCH REPEAT PROTEIN 2 (OsLKP2) function results in drought tolerance in rice due to an elevated total wax load on leaf surfaces through upregulated expression of wax‐related genes. In the nucleus, OsLKP2 interacts with GIGANTEA, whose null mutant also shows enhanced drought tolerance.
The blue-light (BL) receptor, aureochrome was found and isolated from xanthophycean macro alga Vaucheria in 2007. Aureochrome is a BL receptor only in photosynthetic stramenopiles, such as diatoms, ...raphidophycean and brown algae. Aureochrome is composed of a bZIP (basic leucine Zipper) transcription factor domain at the N terminus and a LOV (Light-Oxygen-Voltage) domain at the C terminus. FMN (flavin mononucleotide) binds to LOV domain of aureochrome to function as a BL receptor. After BL irradiation, bZIP binds to cis elements (specific DNA binding sequence) with conformational change of LOV domain and regulates gene expression. These results suggest that various BL responses of photosynthetic stramenopiles are induced via the aureochrome. In this review, we introduce the function of aureochrome and future perspective.
Photoreceptor flavoproteins of the LOV, BLUF, and cryptochrome families are ubiquitous among the three domains of life and are configured as UVA/blue-light systems not only in plants-their original ...arena-but also in prokaryotes and microscopic algae. Here, we review these proteins' structure and function, their biological roles, and their evolution and impact in the living world, and underline their growing application in biotechnologies. We present novel developments such as the interplay of light and redox stimuli, emerging enzymatic and biological functions, lessons on evolution from picoalgae, metagenomics analysis, and optogenetics applications.
Methods to acutely manipulate protein interactions at the subcellular level are powerful tools in cell biology. Several blue-light-dependent optical dimerization tools have been developed. In these ...systems one protein component of the dimer (the bait) is directed to a specific subcellular location, while the other component (the prey) is fused to the protein of interest. Upon illumination, binding of the prey to the bait results in its subcellular redistribution. Here, we compared and quantified the extent of light-dependent dimer occurrence in small, subcellular volumes controlled by three such tools: Cry2/CIB1, iLID, and Magnets. We show that both the location of the photoreceptor protein(s) in the dimer pair and its (their) switch-off kinetics determine the subcellular volume where dimer formation occurs and the amount of protein recruited in the illuminated volume. Efficient spatial confinement of dimer to the area of illumination is achieved when the photosensitive component of the dimerization pair is tethered to the membrane of intracellular compartments and when on and off kinetics are extremely fast, as achieved with iLID or Magnets. Magnets and the iLID variants with the fastest switch-off kinetics induce and maintain protein dimerization in the smallest volume, although this comes at the expense of the total amount of dimer. These findings highlight the distinct features of different optical dimerization systems and will be useful guides in the choice of tools for specific applications.
Bacteria and fungi of the plant microbiota can be phytopathogens, parasites or symbionts that establish mutually advantageous relationships with plants. They are often rich in photoreceptors for ...UVA–Visible light, and in many cases, they exhibit light regulation of growth patterns, infectivity or virulence, reproductive traits, and production of pigments and of metabolites. In addition to the light-driven effects, often demonstrated via the generation of photoreceptor gene knock-outs, microbial photoreceptors can exert effects also in the dark. Interestingly, some fungi switch their attitude towards plants in dependence of illumination or dark conditions in as much as they may be symbiotic or pathogenic. This review summarizes the current knowledge about the roles of light and photoreceptors in plant-associated bacteria and fungi aiming at the identification of common traits and general working ideas. Still, reports on light-driven infection of plants are often restricted to the description of macroscopically observable phenomena, whereas detailed information on the molecular level, e.g., protein–protein interaction during signal transduction or induction mechanisms of infectivity/virulence initiation remains sparse. As it becomes apparent from still only few molecular studies, photoreceptors, often from the red- and the blue light sensitive groups interact and mutually modulate their individual effects. The topic is of great relevance, even in economic terms, referring to plant-pathogen or plant-symbionts interactions, considering the increasing usage of artificial illumination in greenhouses, the possible light-regulation of the synthesis of plant-growth stimulating substances or herbicides by certain symbionts, and the biocontrol of pests by selected fungi and bacteria in a sustainable agriculture.
In Arabidopsis, GIGANTEA (GI), together with the blue-light receptors ZTL, LKP2, and FKF1, regulates degradation of the core clock protein TOC1 and the flowering repressor CDFs, thereby controlling ...circadian oscillation and flowering. Despite the significance of GI in diverse plant physiology, its molecular function is not much understood because of technical problems in protein preparation and a lack of structural information. Here, we report the purification of the GI monomer and the crystal structure of the GI/LKP2 complex. The crystal structure reveals that residues 1–813 of GI possess an elongated rigid structure formed by stacking hydrophobic α-helices and that the LOV domain of LKP2 binds to the middle region of the GI (residues 563–789). Interaction analysis further shows that LOV homodimers are converted to monomers by GI binding. Our results provide structural insights into the regulation of the circadian clock and photoperiodic flowering by GI and ZTL/LKP2/FKF1.
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•GI possesses an elongated rigid structure formed by stacking hydrophobic α-helices•GI forms a heterodimer with the LOV domains of ZTL, LKP2, and FKF1•The LOV domain binds to the middle region of GI at residues 563–789•LOV homodimer is disrupted by GI binding
GIGANTEA (GI) and blue-light receptors contribute to plant circadian rhythm and flowering. Kwon et al. describes the crystal structure of GI in complex with the LOV domain of LKP2 from Arabidopsis thaliana. This reveals the overall structure of GI and its interactions with the LOV domains.
Phototropins are blue-light receptors controlling a range of responses that serve to optimize the photosynthetic efficiency of plants. These include phototropism, light-induced stomatal opening, and ...chloroplast movements in response to changes in light intensity. Since the isolation of the Arabidopsis PHOT1 gene in 1997, phototropins have been identified in ferns and mosses where their physiological functions appear to be conserved. Arabidopsis contains two phototropins, phot1 and phot2, that exhibit overlapping functions in addition to having unique physiological roles. Phototropins are light-activated serine/threonine protein kinases. Light sensing by the phototropins is mediated by a repeated motif at the N-terminal region of the protein known as the LOV domain. Photoexcitation of the LOV domain results in receptor autophosphorylation and an initiation of phototropin signaling. Here we summarize the photochemical and biochemical events underlying phototropin activation in addition to the current knowledge of the molecular mechanisms associated with photoreceptor signaling.
Light-oxygen-voltage (LOV) domains are widespread photosensory modules that can be used in fluorescence microscopy, optogenetics and controlled production of reactive oxygen species. All of the ...currently known LOV domains have absorption maxima in the range of ~440 to ~450 nm, and it is not clear whether they can be shifted significantly using mutations. Here, we have generated a panel of LOV domain variants by mutating the key chromophore-proximal glutamine aminoacid of a thermostable flavin based fluorescent protein CagFbFP (Gln148) to asparagine, aspartate, glutamate, histidine, lysine and arginine. Absorption spectra of all of the mutants are blue-shifted, with the maximal shift of 8 nm observed for the Q148H variant. While CagFbFP and its Q148N/D/E variants are not sensitive to pH, Q148H/K/R reveal a moderate red shift induced byacidic pH. To gain further insight, we determined high resolution crystal structures of all of the mutants studied at the resolutions from 1.07 Å for Q148D to 1.63 Å for Q148R. Whereas in some of the variants, the aminoacid 148 remains in the vicinity of the flavin, in Q148K, Q148R and partially Q148D, the C-terminus of the protein unlatches and the side chain of the residue 148 is reoriented away from the chromophore. Our results explain the absence of color shifts from replacing Gln148 with charged aminoacids and pave the way for rational design of color-shifted flavin based fluorescent proteins.
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