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Sunflowers are famous for their ability to track the sun throughout the day and then reorient at night to face east the following morning. This occurs by differential growth patterns, with the east sides of stems growing more during the day and the west sides of stems growing more at night. This process, termed heliotropism, is generally believed to be a specialized form of phototropism; however, the underlying mechanism is unknown. To better understand heliotropism, we compared gene expression patterns in plants undergoing phototropism in a controlled environment and in plants initiating and maintaining heliotropic growth in the field. We found the expected transcriptome signatures of phototropin-mediated phototropism in sunflower stems bending towards monochromatic blue light. Surprisingly, the expression patterns of these phototropism-regulated genes are quite different in heliotropic plants. Most genes rapidly induced during phototropism display only minor differences in expression across solar tracking stems. However, some genes that are both rapidly induced during phototropism and are implicated in growth responses to foliar shade are rapidly induced on the west sides of stems at the onset of heliotropism, suggesting a possible role for red light photoreceptors in solar tracking. To test the involvement of different photoreceptor signaling pathways in heliotropism, we modulated the light environment of plants initiating solar tracking. We found that depletion of either red and far-red light or blue light did not hinder the initiation or maintenance of heliotropism in the field. Together, our results suggest that the transcriptional regulation of heliotropism is distinct from phototropin-mediated phototropism and likely involves inputs from multiple light signaling pathways.

Chloroplast movement rapidly ameliorates the effects of suboptimal light intensity by accumulating along the periclinal cell walls, as well as the effects of excess light by shifting to the anticlinal cell walls. These acclimation responses are triggered by phototropins located at the plasma membrane and chloroplast envelope. Here, we used a recently developed non-invasive system sensitive to very small changes in red light leaf transmittance to perform long-term continuous measurements of dark–light transitions. As a model system, we used variegated Pelargonium zonale leaves containing green sectors (GS) with fully developed chloroplasts and achlorophyllous, white sectors (WS) with undifferentiated plastids, and higher phototropin expression levels. We observed biphasic changes in the red-light transmittance and oscillations triggered by medium intensities of white light, described by a transient peak preceded by a constant decrease in transmittance level. A slight change in red-light transmittance was recorded even in WS. Furthermore, the chloroplast position at lower light intensities affected the rapid light curves, while high light intensity decreased saturated electron transport, maximum quantum efficiency of photosystem II, and increased non-photochemical quenching of chlorophyll fluorescence and epidermal flavonoids. Our results extend the knowledge of light-dependent chloroplast movements and thus contribute to a better understanding of their role in regulating photosynthesis under fluctuating light conditions. [ABSTRACT FROM AUTHOR]

In this contribution, we describe a brief overview of the role of different light-signaling proteins in different biochemical processes (mostly in plants) along the electromagnetic spectrum. We also revise, in terms of perspectives, the applications of all these proteins to optogenetics as a new emerging field of research. In the second part, we present some case studies: First, we used two fluorescent proteins showing an optical response in the green- and red-light wavelengths both isolated from marines' organisms, which were incorporated as light sensors into the silico-carbonate of Ca, Ba, and Sr (usually called biomorphs). The second case study consisted in incorporating phototropins from a plant (Arabidopsis thaliana) into the synthesis of biomorphs. Finally, the last part analyses the influence of these three proteins on the shape and structure in the synthesis of silico-carbonates of calcium, barium, and strontium as optical sensors, in order to detect the location of these biomolecules inside these self-assembly crystalline materials called biomorphs. [ABSTRACT FROM AUTHOR]

Protein tyrosine phosphatases regulate a myriad of essential subcellular signaling events, yet they remain difficult to study in their native biophysical context. Here we develop a minimally disruptive optical approach to control protein tyrosine phosphatase 1B (PTP1B)-an important regulator of receptor tyrosine kinases and a therapeutic target for the treatment of diabetes, obesity, and cancer-and we use that approach to probe the intracellular function of this enzyme. Our conservative architecture for photocontrol, which consists of a protein-based light switch fused to an allosteric regulatory element, preserves the native structure, activity, and subcellular localization of PTP1B, affords changes in activity that match those elicited by post-translational modifications inside the cell, and permits experimental analyses of the molecular basis of optical modulation. Findings indicate, most strikingly, that small changes in the activity of PTP1B can cause large shifts in the phosphorylation states of its regulatory targets.

Abstract Background Glutamate receptor-like (GLR) channels are plant homologs of iGluRs, animal ionotropic glutamate receptors which participate in neurotransmission. GLRs mediate plant adaptive processes and photomorphogenesis. Despite their contribution to light-dependent processes, signaling mechanisms that modulate GLR response to light remain unknown. Here we show that leaf expression of 7 out of 20 Arabidopsis GLRs is significantly up-regulated by monochromatic irradiation. Results Our data indicates that both red and blue light stimulate the expression of selected AtGLRs. Using a photosynthesis inhibitor and different irradiation regimes, we demonstrated that retrograde signaling from photosystem II is unlikely to be involved in light-dependent GLR up-regulation. Analysis of transcriptional patterns in mutants of key photoreceptors allowed us to observe that both phytochromes and cryptochromes are likely to be involved in the control of light-dependent up-regulation of AtGLR expression, with phytochromes playing a clearly dominating role in this process. Conclusions In mature Arabidopsis leaves, phytochromes, assisted by cryptochromes, mediate light-driven transcriptional up-regulation of several genes encoding GLR proteins. Since GLRs are known to be involved in a wide range of plant developmental processes our results provide mechanistic insight into how light may influence plant growth and development.

In this contribution, we describe a brief overview of the role of different light-signaling proteins in different biochemical processes (mostly in plants) along the electromagnetic spectrum. We also revise, in terms of perspectives, the applications of all these proteins to optogenetics as a new emerging field of research. In the second part, we present some case studies: First, we used two fluorescent proteins showing an optical response in the green- and red-light wavelengths both isolated from marines’ organisms, which were incorporated as light sensors into the silico-carbonate of Ca, Ba, and Sr (usually called biomorphs). The second case study consisted in incorporating phototropins from a plant (Arabidopsis thaliana) into the synthesis of biomorphs. Finally, the last part analyses the influence of these three proteins on the shape and structure in the synthesis of silico-carbonates of calcium, barium, and strontium as optical sensors, in order to detect the location of these biomolecules inside these self-assembly crystalline materials called biomorphs.

In many legumes, roots that are exposed to light do not form nodules. Here, we report that blue light inhibits nodulation in Lotus japonicus roots inoculated with Mesorhizobium loti. Using RNA interference, we suppressed the expression of the phototropin and cryptochrome genes in L. japonicus hairy roots. Under blue light, plants transformed with an empty vector did not develop nodules, whereas plants exhibiting suppressed expression of cry1 and cry2 genes formed nodules. We also measured rhizobial growth to investigate whether the inhibition of nodulation could be caused by a reduced population of rhizobia in response to light. Although red light had no effect on rhizobial growth, blue light had a strong inhibitory effect. Rhizobial growth under blue light was partially restored in signature-tagged mutagenesis (STM) strains in which LOV-HK/PAS- and photolyase-related genes were disrupted. Moreover, when Ljcry1A and Ljcry2B-silenced plants were inoculated with the STM strains, nodulation was additively increased. Our data show that blue light receptors in both the host plant and the symbiont have a profound effect on nodule development. The exact mechanism by which these photomorphogenetic responses function in the symbiosis needs further study, but they are clearly involved in optimizing legume nodulation.

Background: Glutamate receptor-like (GLR) channels are plant homologs of iGluRs, animal ionotropic glutamate receptors which participate in neurotransmission. GLRs mediate plant adaptive processes and photomorphogenesis. Despite their contribution to light-dependent processes, signaling mechanisms that modulate GLR response to light remain unknown. Here we show that leaf expression of 7 out of 20 Arabidopsis GLRs is significantly up-regulated by monochromatic irradiation. Results: Our data indicates that both red and blue light stimulate the expression of selected AtGLRs. Using a photosynthesis inhibitor and different irradiation regimes, we demonstrated that retrograde signaling from photosystem II is unlikely to be involved in light-dependent GLR up-regulation. Analysis of transcriptional patterns in mutants of key photoreceptors allowed us to observe that both phytochromes and cryptochromes are likely to be involved in the control of light-dependent up-regulation of AtGLR expression, with phytochromes playing a clearly dominating role in this process. Conclusions: In mature Arabidopsis leaves, phytochromes, assisted by cryptochromes, mediate light-driven transcriptional up-regulation of several genes encoding GLR proteins. Since GLRs are known to be involved in a wide range of plant developmental processes our results provide mechanistic insight into how light may influence plant growth and development. [ABSTRACT FROM AUTHOR]

Light and temperature are two essential environmental cues for plants, helping to optimize plant body architecture and physiology. To sense a broad spectrum of sun radiation spanning from UV-B to far-red wavelength, plants are equipped with a sophisticated array of photoreceptors, including phytochromes, cryptochromes, phototropins, Zeitlupes, and UV-B photoreceptor UVR8. On the contrary, since the thermodynamic effects extensively affect the molecular and supramolecular structures, it is difficult to identify the entry point or initial receptor of temperature. Even so, several putative temperature sensors have been proposed, such as calcium ion channels, H2A.Z, and the thermodynamic change of plasma membrane fluidity. Considering that many processes in plant respond to irradiance and temperature, scientists devote to finding out the converge point of these environmental cues. As a typical example, circadian rhythm is such an integration point, which receives the signal input of both irradiance and temperature. The updating evidence shows, as an important photoreceptor, phytochrome B acts as temperature sensors via a thermodynamic active state revision. These findings suggest that the studies on light and temperature receptors in plants should not be separated. Their extensive convergence during signalling provides a new direction for understanding the stimuli perception mechanisms.

Plants adapt to environmental light conditions by photoreceptor-mediated physiological responses, but the mechanism by which photoreceptors perceive and transduce the signals is still unresolved. Here, we used 2D difference gel electrophoresis (2D DIGE) and mass spectrometry to characterize early molecular events induced by short blue light exposures in etiolated Arabidopsis seedlings. We observed the phosphorylation of phototropin 1 (phot1) and accumulation of weak chloroplast movement under blue light 1 (WEB1) in the membrane fraction after blue light irradiation. Over 50 spots could be observed for the two rows of phot1 spots in the 2-DE gels, and eight novel phosphorylated Ser/Thr sites were identified in the N-terminus and Hinge 1 regions of phot1 in vivo. Blue light caused ubiquitination of phot1, and K526 of phot1 was identified as a putative ubiquitination site. Our study indicates that post-translational modification of phot1 is more complex than previously reported.

SUMMARY: Phototropins, the UVA‐blue light photoreceptors, endow plants to detect the direction of light and optimize photosynthesis by regulating positioning of chloroplasts and stomatal gas exchange. Little is known about their functions in other developmental responses. A tomato Non‐phototropic seedling1 (Nps1) mutant, bearing an Arg495His substitution in the vicinity of LOV2 domain in phototropin1, dominant‐negatively blocks phototropin1 responses. The fruits of Nps1 mutant were enriched in carotenoids, particularly lycopene, compared with its parent, Ailsa Craig. On the contrary, CRISPR/CAS9‐edited loss of function phototropin1 mutants displayed subdued carotenoids compared with the parent. The enrichment of carotenoids in Nps1 fruits is genetically linked with the mutation and exerted in a dominant‐negative fashion. Nps1 also altered volatile profiles with high levels of lycopene‐derived 6‐methyl 5‐hepten2‐one. The transcript levels of several MEP and carotenogenesis pathway genes were upregulated in Nps1. Nps1 fruits showed altered hormonal profiles with subdued ethylene emission and reduced respiration. Proteome profiles showed a causal link between higher carotenogenesis and increased levels of protein protection machinery, which may stabilize proteins contributing to MEP and carotenogenesis pathways. The enhancement of carotenoid content by Nps1 in a dominant‐negative fashion offers a potential tool for high lycopene‐bearing hybrid tomatoes. [ABSTRACT FROM AUTHOR]

Electron microscopy (EM) achieves the highest spatial resolution in protein localization, but specific protein EM labeling has lacked generally applicable genetically encoded tags for in situ visualization in cells and tissues. Here we introduce "miniSOG" (for mini Singlet Oxygen Generator), a fluorescent flavoprotein engineered from Arabidopsis phototropin 2. MiniSOG contains 106 amino acids, less than half the size of Green Fluorescent Protein. Illumination of miniSOG generates sufficient singlet oxygen to locally catalyze the polymerization of diaminobenzidine into an osmiophilic reaction product resolvable by EM. MiniSOG fusions to many well-characterized proteins localize correctly in mammalian cells, intact nematodes, and rodents, enabling correlated fluorescence and EM from large volumes of tissue after strong aldehyde fixation, without the need for exogenous ligands, probes, or destructive permeabilizing detergents. MiniSOG permits high quality ultrastructural preservation and 3-dimensional protein localization via electron tomography or serial section block face scanning electron microscopy. EM shows that miniSOG-tagged SynCAM1 is presynaptic in cultured cortical neurons, whereas miniSOG-tagged SynCAM2 is postsynaptic in culture and in intact mice. Thus SynCAM1 and SynCAM2 could be heterophilic partners. MiniSOG may do for EM what Green Fluorescent Protein did for fluorescence microscopy.

Premise: The importance of chloroplast movement for plant growth in constant, controlled light and of nonphotochemical quenching (NPQ) in variable, natural light are known. Here we concurrently investigated growth and reproduction of several Arabidopsis thaliana mutants to assess the relative importance of photoprotection via chloroplast movement and NPQ. Methods: Plants were grown outdoors (natural conditions) or in a growth chamber with variable light and chilling temperatures (controlled conditions). Phenotypic growth and reproductive variables were determined at set times before maturity in wild‐type (WT) and phot1, phot2, phot1phot2 (e.g., impaired chloroplast movement, stomatal conductance, leaf flattening), chup1 (impaired chloroplast movement), and npq1 (reduced NPQ) plants. Results: Mutants were most adversely affected in natural conditions, with phot1phot2 and chup1 most severely impacted. These mutants bolted later and produced fewer leaves and siliques, less leaf biomass, and fewer secondary inflorescences than WT. In controlled conditions, leaf traits of these mutants were unaffected, but phot1phot2 bolted later and produced fewer secondary inflorescences and siliques than WT. For most variables, there were significant interactions between growth conditions and plant genotype. Many variables were correlated, but those relationships changed with growth conditions and genotype. Conclusions: Phenotypic variables at the time of the harvest were strongly affected by growth conditions and genotype. In natural conditions, phot1phot2 and chup1 mutants were most adversely affected, demonstrating the importance of chloroplast movement. In controlled conditions, only phot1phot2 was consistently affected, also emphasizing the important, pleiotropic effects of phototropins. In both conditions, NPQ was less important. [ABSTRACT FROM AUTHOR]

Light and temperature are two essential environmental cues for plants, helping to optimize plant body architecture and physiology. To sense a broad spectrum of sun radiation spanning from UV-B to far-red wavelength, plants are equipped with a sophisticated array of photoreceptors, including phytochromes, cryptochromes, phototropins, Zeitlupes, and UV-B photoreceptor UVR8. On the contrary, since the thermodynamic effects extensively affect the molecular and supramolecular structures, it is difficult to identify the entry point or initial receptor of temperature. Even so, several putative temperature sensors have been proposed, such as calcium ion channels, H2A.Z, and the thermodynamic change of plasma membrane fluidity. Considering that many processes in plant respond to irradiance and temperature, scientists devote to finding out the converge point of these environmental cues. As a typical example, circadian rhythm is such an integration point, which receives the signal input of both irradiance and temperature. The updating evidence shows, as an important photoreceptor, phytochrome B acts as temperature sensors via a thermodynamic active state revision. These findings suggest that the studies on light and temperature receptors in plants should not be separated. Their extensive convergence during signalling provides a new direction for understanding the stimuli perception mechanisms. [ABSTRACT FROM AUTHOR]

Summary: Plant morphological and physiological traits exhibit plasticity in response to light intensity. Leaf thickness is enhanced under high light (HL) conditions compared with low light (LL) conditions through increases in both cell number and size in the dorsoventral direction; however, the regulation of such phenotypic plasticity in leaf thickness (namely, sun‐ or shade‐leaf formation) during the developmental process remains largely unclear. By modifying observation techniques for tiny leaf primordia in Arabidopsis thaliana, we analysed sun‐ and shade‐leaf development in a time‐course manner and found that the process of leaf thickening can be divided into early and late phases. In the early phase, anisotropic cell elongation and periclinal cell division on the adaxial side of mesophyll tissue occurred under the HL conditions used, which resulted in the dorsoventral growth of sun leaves. Anisotropic cell elongation in the palisade tissue is triggered by blue‐light irradiation. We discovered that anisotropic cell elongation processes before or after periclinal cell division were differentially regulated independent of or dependent upon signalling through blue‐light receptors. In contrast, during the late phase, isotropic cell expansion associated with the endocycle, which determined the final leaf thickness, occurred irrespective of the light conditions. Sucrose production was high under HL conditions, and we found that sucrose promoted isotropic cell expansion and the endocycle even under LL conditions. Our analyses based on this method of time‐course observation addressed the developmental framework of sun‐ and shade‐leaf formation. Significance Statement: Thick sun leaves or thin shade leaves develop in response to light intensity, but the mechanism involved in leaf‐thickness growth is unclear. Based on high‐resolution sectional images of leaf primordia, we identified two distinct developmental stages. During the early stage, intense light triggers changes in cell shape via blue‐light receptors. During the later stage, sucrose enhances the isotropic enlargement of cells. Taken together, these results provide insight into sun‐leaf formation. [ABSTRACT FROM AUTHOR]

The photon flux in the green wavelength region is relatively enriched in shade and the photon flux in the blue region is selectively filtered. In sole source lighting environments, increasing the fraction of blue typically decreases stem elongation and leaf expansion, and smaller leaves reduce photon capture and yield. Photons in the green region reverse these blue reductions through the photoreceptor cryptochrome in Arabidopsis thaliana, but studies in other species have not consistently shown the benefits of photons in the green region on leaf expansion and growth. Spectral effects can interact with total photon flux. Here, we report the effect of the fraction of photons in the blue (10 to 30%) and green (0 to 50%) regions at photosynthetic photon flux densities of 200 and 500 µmol m−2 s−1 in lettuce, cucumber and tomato. As expected, increasing the fraction of photons in the blue region consistently decreased leaf area and dry mass. By contrast, large changes in the fraction of photons in the green region had minimal effects on leaf area and dry mass in lettuce and cucumber. Photons in the green region were more potent at a lower fraction of photons in the blue region. Photons in the green region increased stem and petiole length in cucumber and tomato, which is a classic shade avoidance response. These results suggest that high-light crop species might respond to the fraction of photons in the green region with either shade tolerance (leaf expansion) or shade avoidance (stem elongation).

Phototropins are plasma membrane-associated photoreceptors of blue light and UV-A/B radiation. The Arabidopsis thaliana genome encodes two phototropins, PHOT1 and PHOT2, that mediate phototropism, chloroplast positioning, and stomatal opening. They are well characterized in terms of photomorphogenetic processes, but so far, little was known about their involvement in photosynthesis, oxidative stress responses, and cell death. By analyzing phot1, phot2 single, and phot1phot2 double mutants, we demonstrated that both phototropins influence the photochemical and non-photochemical reactions, photosynthetic pigments composition, stomata conductance, and water-use efficiency. After oxidative stress caused by UV-C treatment, phot1 and phot2 single and double mutants showed a significantly reduced accumulation of H2O2 and more efficient photosynthetic electron transport compared to the wild type. However, all phot mutants exhibited higher levels of cell death four days after UV-C treatment, as well as deregulated gene expression. Taken together, our results reveal that on the one hand, both phot1 and phot2 contribute to the inhibition of UV-C-induced foliar cell death, but on the other hand, they also contribute to the maintenance of foliar H2O2 levels and optimal intensity of photochemical reactions and non-photochemical quenching after an exposure to UV-C stress. Our data indicate a novel role for phototropins in the condition-dependent optimization of photosynthesis, growth, and water-use efficiency as well as oxidative stress and cell death response after UV-C exposure.

The biomineralization process is a mechanism inherent to all organisms of the Earth. Throughout the decades, diverse works have reported that the origin of life is tied to crystals, specifically to biominerals of silica that catalyzed RNA, and had some influence in the homochirality. Although the mechanism by which crystals surfaces (minerals) gave origin to life has not yet been proven, the truth is that, up to the present, biominerals are being synthetized by the organisms of different kingdoms in two basic ways: biologically induced and biologically controlled biomineralization. Paradoxically, this fact makes a fundamental difference between inorganic materials and those formed by living organisms, as the latter are associated with macromolecules that are bound to the mineral phase. Conserving growth and formation of these biogenic organic crystals inside cells is a fascinating subject that has been studied mainly in some of the kingdoms, like Monera (bacteria), Fungi (yeasts), and Animalia (Homo sapiens). Notwithstanding in the Plantae kingdom, the formation, conservation, and functions of crystals has not yet been completely elucidated and described, which is of particular relevance because life on Earth, as we know it, would not be possible without plants. The aim of the present work is to revise the different crystals of calcium oxalate synthetized inside the cells of plants, as well as to identify the mechanism of their formation and their possible functions in plants. The last part is related to the existence of certain proteins called phototropins, which not only work as the blue-light sensors, but they also play an important role on the accumulation of calcium in vacuoles. This new trend is shortly reviewed to explain the characteristics and their plausible role in the calcium uptake along with the biomineralization processes.

Ferns are unique among land plants in having sporophyte and gametophyte phases that are both free living and fully independent. Here, we examine patterns of sporophytic and gametophytic gene expression in the fern Polypodium amorphum, a member of the homosporous polypod lineage that comprises 80% of extant fern diversity, to assess how expression of a common genome is partitioned between two morphologically, ecologically, and nutritionally independent phases. Using RNA-sequencing, we generated transcriptome profiles for three replicates of paired samples of sporophyte leaf tissue and whole gametophytes to identify genes with significant differences in expression between the two phases. We found a nearly 90% overlap in the identity and expression levels of the genes expressed in both sporophytes and gametophytes, with less than 3% of genes uniquely expressed in either phase. We compare our results to those from similar studies to establish how phase-specific gene expression varies among major land plant lineages. Notably, despite having greater similarity in the identity of gene families shared between P. amorphum and angiosperms, P. amorphum has phase-specific gene expression profiles that are more like bryophytes and lycophytes than seed plants. Our findings suggest that shared patterns of phase-specific gene expression among seed-free plants likely reflect having relatively large, photosynthetic gametophytes (compared to the gametophytes of seed plants that are highly reduced). Phylogenetic analyses were used to further investigate the evolution of phase-specific expression for the phototropin, terpene synthase, and MADS-box gene families.

Blue light (BL) is a fundamental cue for stomatal opening in both C3 and C4 plants. However, it is unknown whether crassulacean acid metabolism (CAM) plants open their stomata in response to BL. We investigated stomatal BL responses in the obligate CAM plants Kalanchoe pinnata and Kalanchoe daigremontiana that characteristically open their stomata at night and close them for part of the day, as contrasted with C3 and C4 plants. Stomata opened in response to weak BL superimposed on background red light in both intact leaves and detached epidermal peels of K. pinnata and K. daigremontiana. BL-dependent stomatal opening was completely inhibited by tautomycin and vanadate, which repress type 1 protein phosphatase and plasma membrane H+-ATPase, respectively. The plasma membrane H+-ATPase activator fusicoccin induced stomatal opening in the dark. Both BL and fusicoccin induced phosphorylation of the guard cell plasma membrane H+-ATPase in K. pinnata. These results indicate that BL-dependent stomatal opening occurs in the obligate CAM plants K. pinnata and K. daigremontiana independently of photosynthetic CO2 assimilation mode. [ABSTRACT FROM AUTHOR]

The rpt2-2 single mutant lost phototropism, but phot1 rpt2-2 double mutant shows phototropic response, indicating that PHOT1 has a function in inhibiting hypocotyl phototropism, and RPT2 maybe play vital role in these prosses. Here, we used RPT2 as bait protein to screen yeast library and successfully obtained six proteins interacted with RPT2 including JAC1 and PHOT1. Yeast hybridization verified that four of these proteins could interact with RPT2. Phenotypic analysis of two mutants of gene RIP1 showed that the single mutant rip1-1 and rip1-2 had normal phototropism in response to high blue light, but rpt2-2 rip1-1 and rpt2-2 rip1-2 double mutant were defective in phototropism, similar with the phot1 rpt2-2 double mutant. These results suggested that this protein may modulate PHOT1-mediated high blue light inhibitory response. Functional analysis of this protein will be helpful to promote the discovery of the mechanism of phot1-mediated inhibitory response. [ABSTRACT FROM AUTHOR]

Phototropins (phot1 and phot2) are blue-light receptors that control cotyledon flattening and positioning under strong light; however, their functional redundancy restricts our understanding of the specific roles of phot2. To identify the factors responsible for phot2-dependent cotyledon flattening and growth, we screened for light-insensitive mutants among mutagenized phot1 mutants in Arabidopsis thaliana. The double mutant phot1 lea1 (leaf expansion associated 1), which is defective in cotyledon flattening and positioning but not the phototropic response was selected. This mutant phenotype could be alleviated by constitutively expressing MORE AXILLARY GROWTH 2 (MAX2), indicating that LEA1 was allelic to MAX2. The max2 mutants (max2-2 and max2-3) are defective in cotyledon flattening, which is similar to that of the phot1 phot2 mutants. Moreover, the amounts of MAX2 transcripts are inhibited in leaves of phot1 mutant. However, the additional disruption of PHOT1 gene in max2-2 or max2-3 did not affect their phenotype, including MAX2-mediated inhibition of hypocotyl elongation. By contrast, phototropins-mediated hypocotyl phototropism was not regulated by MAX2. Together, these results suggest that cotyledon flattening was mediated by both phototropins and MAX2 signaling, but the relationship between two pathways need further study. [ABSTRACT FROM AUTHOR]

Ferns are unique among land plants in having sporophyte and gametophyte phases that are both free living and fully independent. Here, we examine patterns of sporophytic and gametophytic gene expression in the fern Polypodium amorphum , a member of the homosporous polypod lineage that comprises 80% of extant fern diversity, to assess how expression of a common genome is partitioned between two morphologically, ecologically, and nutritionally independent phases. Using RNA-sequencing, we generated transcriptome profiles for three replicates of paired samples of sporophyte leaf tissue and whole gametophytes to identify genes with significant differences in expression between the two phases. We found a nearly 90% overlap in the identity and expression levels of the genes expressed in both sporophytes and gametophytes, with less than 3% of genes uniquely expressed in either phase. We compare our results to those from similar studies to establish how phase-specific gene expression varies among major land plant lineages. Notably, despite having greater similarity in the identity of gene families shared between P. amorphum and angiosperms, P. amorphum has phase-specific gene expression profiles that are more like bryophytes and lycophytes than seed plants. Our findings suggest that shared patterns of phase-specific gene expression among seed-free plants likely reflect having relatively large, photosynthetic gametophytes (compared to the gametophytes of seed plants that are highly reduced). Phylogenetic analyses were used to further investigate the evolution of phase-specific expression for the phototropin, terpene synthase, and MADS-box gene families. [ABSTRACT FROM AUTHOR]

Stream ecosystems are affected by multiple anthropogenic stressors worldwide. Even though effects of many single stressors are comparatively well studied, the effects of multiple stressors are difficult to predict. In particular bacteria and protists, which are responsible for the majority of ecosystem respiration and element flows, are infrequently studied with respect to multiple stressors responses. We conducted a stream mesocosm experiment to characterize the responses of single and multiple stressors on microbiota. Two functionally important stream habitats, leaf litter and benthic phototrophic rock biofilms, were exposed to three stressors in a full factorial design: fine sediment deposition, increased chloride concentration (salinization) and reduced flow velocity. We analyzed the microbial composition in the two habitat types of the mesocosms using an amplicon sequencing approach. Community analysis on different taxonomic levels as well as principle component analyses (PCoAs) based on realtive abundances of operational taxonomic units (OTUs) showed treatment specific shifts in the eukaryotic biofilm community. Analysis of variance (ANOVA) revealed that Bacillariophyta responded positively salinity and sediment increase, while the relative read abundance of chlorophyte taxa decreased. The combined effects of multiple stressors were mainly antagonistic. Therefore, the community composition in multiply stressed environments resembled the composition of the unstressed control community in terms of OTU occurrence and relative abundances. [ABSTRACT FROM AUTHOR]

The geomagnetic field (GMF) is an environmental element whose instability affects plant growth and development. Despite known plant responses to GMF direction and intensity, the mechanism of magnetoreception in plants is still not known. Magnetic field variations affect many light-dependent plant processes, suggesting that the magnetoreception could require light. The objective of this work was to comprehensively investigate the influence of GMF on Arabidopsis thaliana ( Col-0 ) photoreceptor signaling. Wild-type Arabidopsis seedlings and photoreceptor-deficient mutants ( cry1cry2 , phot1 , phyA and phyAphyB ) were exposed to near null magnetic field (NNMF, ≤40 nT) and GMF (~43 μT) under darkness and different light wavelengths. The GMF did not alter skotomorphogenic or photomorphogenic seedling development but had a significant impact on gene expression pathways downstream of cryptochrome and phytochrome photoactivation. GMF-induced changes in gene expression observed under blue light were partially associated with an alteration of cryptochrome activation. GMF impacts on phytochrome-regulated gene expression could be attributed to alterations in phytochrome protein abundance that were also dependent on the presence of cry1, cry2 and phot1. Moreover, the GMF was found to impact photomorphogenic-promoting gene expression in etiolated seedlings, indicating the existence of a light-independent magnetoreception mechanism. In conclusion, our data shows that magnetoreception alters photoreceptor signaling in Arabidopsis, but it does not necessarily depend on light. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an essential macronutrient for plant life, although it is frequently not readily available to crops. Arbuscular mycorrhiza fungi (AMF) can improve plant P levels by inducing the expression of some phosphate (Pi) transporters. Symbiotic Pi uptake by Pi transporters is crucial for AMF colonization and arbuscule dynamics. However, the functions of mycorrhiza-inducible maize Pi transporters are largely unclear. We focused on the interaction between the Pi concentration and AMF colonization in maize, and detecting the induction of a Pi transporter. We investigated AMF colonization and arbuscular development in maize under high and low Pi environments. Low Pi increased AMF colonization and promoted arbuscular development. Further measurement of P concentration showed that AMF significantly improved the maize P status under low Pi conditions. Here, we identified the Pi transporter gene, ZmPt9, which was induced by mycorrhiza formation. In addition, ZmPt9 -overexpressing roots were difficult to colonize by AMF. Pi response analysis showed that ZmPt9 complements a yeast mutant defective in Pi transporter activity and improves the P concentration in rice. Together, these data indicated that ZmPt9 is a mycorrhiza-inducible Pi transporter gene involved in Pi uptake. [ABSTRACT FROM AUTHOR]

Regulation of stomatal aperture is essential for plant growth and survival in response to environmental stimuli. Opening of stomata induces uptake of CO2 for photosynthesis and transpiration, which enhances uptake of nutrients from roots. Light is the most important stimulus for stomatal opening. Under drought stress, the plant hormone ABA induces stomatal closure to prevent water loss. However, the molecular mechanisms of stomatal movements are not fully understood. In this study, we screened chemical libraries to identify compounds that affect stomatal movements in Commelina benghalensis and characterize the underlying molecular mechanisms. We identified nine stomatal closing compounds (SCL1–SCL9) that suppress light-induced stomatal opening by >50%, and two compounds (temsirolimus and CP-100356) that induce stomatal opening in the dark. Further investigations revealed that SCL1 and SCL2 had no effect on autophosphorylation of phototropin or the activity of the inward-rectifying plasma membrane (PM) K+ channel, KAT1, but suppressed blue light-induced phosphorylation of the penultimate residue, threonine, in PM H+-ATPase, which is a key enzyme for stomatal opening. SCL1 and SCL2 had no effect on ABA-dependent responses, including seed germination and expression of ABA-induced genes. These results suggest that SCL1 and SCL2 suppress light-induced stomatal opening at least in part by inhibiting blue light-induced activation of PM H+-ATPase, but not by the ABA signaling pathway. Interestingly, spraying leaves onto dicot and monocot plants with SCL1 suppressed wilting of leaves, indicating that inhibition of stomatal opening by these compounds confers tolerance to drought stress in plants. [ABSTRACT FROM AUTHOR]

Regulation of protein function by phosphorylation and dephosphorylation is an important mechanism in many cellular events. The phototropin blue-light photoreceptors, plant-specific AGCVIII kinases, are essential for phototropic responses. Members of the D6 PROTEIN KINASE (D6PK) family, representing a subfamily of the AGCVIII kinases, also contribute to phototropic responses, suggesting that possibly further AGCVIII kinases may potentially control phototropism. The present study investigates the functional roles of Arabidopsis (Arabidopsis thaliana) AGCVIII kinases in hypocotyl phototropism. We demonstrate that D6PK family kinases are not only required for the second but also for the first positive phototropism. In addition, we find that a previously uncharacterized AGCVIII protein, AGC1-12, is involved in the first positive phototropism and gravitropism. AGC1-12 phosphorylates serine residues in the cytoplasmic loop of PIN-FORMED 1 (PIN1) and shares phosphosite preferences with D6PK. Our work strongly suggests that the D6PK family and AGC1-12 are critical components for both hypocotyl phototropism and gravitropism, and that these kinases control tropic responses mainly through regulation of PIN-mediated auxin transport by protein phosphorylation. [ABSTRACT FROM AUTHOR]

Abstract Phototropism is a growth response allowing plants to align their photosynthetic organs toward incoming light and thereby to optimize photosynthetic activity. Formation of a lateral gradient of the phytohormone auxin is a key step to trigger asymmetric growth of the shoot leading to phototropic reorientation. To identify important regulators of auxin gradient formation, we developed an auxin flux model that enabled us to test in silico the impact of different morphological and biophysical parameters on gradient formation, including the contribution of the extracellular space (cell wall) or apoplast. Our model indicates that cell size, cell distributions, and apoplast thickness are all important factors affecting gradient formation. Among all tested variables, regulation of apoplastic pH was the most important to enable the formation of a lateral auxin gradient. To test this prediction, we interfered with the activity of plasma membrane H+‐ATPases that are required to control apoplastic pH. Our results show that H+‐ATPases are indeed important for the establishment of a lateral auxin gradient and phototropism. Moreover, we show that during phototropism, H+‐ATPase activity is regulated by the phototropin photoreceptors, providing a mechanism by which light influences apoplastic pH.

Plant movements in response to directional solar radiation, known as “heliotropism” are frequently observed in nature. Although there is a considerable amount of literature on these movements in vegetative organs, knowledge about heliotropic responses in flowers and inflorescences is relatively limited. Here we comprehensively review studies on this topic, profile the diversity of responses encompassed under the term “heliotropism” and propose a conceptual framework for their classification. In addition, we discuss the mechanisms underlying different types of heliotropism in two species commonly used as model systems: Arabidopsis and sunflower. Finally, the ecological consequences of floral heliotropism are elaborated with an emphasis on the effects on plant reproductive success, and the potential agricultural implications of manipulating heliotropic responses are addressed as well. We conclude that inflorescence heliotropism appears conserved in many plant species that depend on pollinators, and consists of an auxin dependent response to solar radiation. [ABSTRACT FROM AUTHOR]

Phototropin is a blue light sensor protein found in higher plants and green algae. Photochemical reactions of a variety of differently truncated constructs of a phototropin from Chlamydomonas reinhardtii (Cr) (LOV1, LOV1-hinge, LOV2, LOV2-linker, and hinge-LOV2) are investigated. In the dark state, LOV1 is in dynamic equilibrium between the monomer and dimer, and the main photochemical reaction is dimerization of the monomer and dissociation of the dimer. On the other hand, LOV1-hinge exists as the monomer and the photochemical reaction is the dimerization reaction associated with the unfolding of the helix of the hinge domain. LOV2 in the dark state is monomeric. The conformation changes after the photoexcitation of LOV2 and LOV2-linker are minor, which differs notably from the reaction of LOV2-Jα and LOV2-linker from Arabidopsis thaliana (At). The linker region, including the Jα helix, is rather stable upon photoexcitation. The helix of the hinge domain of hinge-LOV2 is slightly unfolded in the dark state, and the major photoreaction is the dimerization event. The dark recovery rate of LOV2 was found to decrease significantly in the presence of the hinge domain. These photochemical properties of Cr phot are considerably different from those of At phot regarding conformational changes and their kinetics, although Cr phot has been reported to rescue the phot function in At. The differences and the diversity of phots are discussed. [ABSTRACT FROM AUTHOR]

Contents Summary 1029 I. Introduction 1029 II. Convergence at the receptor 1030 III. Convergence at transcriptional hubs 1031 IV. Convergence involving clock components 1033 V. Conclusions 1033 Acknowledgements 1033 References 1033 Summary: The combined information provided by light and temperature cues helps to optimise plant body architecture and physiology. Plants possess elaborate systems to sense and respond to these stimuli. Simultaneous perception of light and temperature by dual receptors such as phytochrome B and phototropin leads to immediate signalling convergence. Conversely, cue asynchronies initiate separate pathways and the information of the earliest cue is stored, awaiting the arrival of the later cue to control transcription. Storage mechanisms can involve changes in the activity of selected clock components or epigenetic modifications, depending on the time delay between cues (hours, days or several months). We propose a conceptual framework in which the mechanisms of integration relate to the timing of cue sensing. [ABSTRACT FROM AUTHOR]

Phototropin2 (phot2) is a blue-light (BL) receptor that regulates BL-dependent activities for efficient photosynthesis in plants. phot2 comprises two BL-receiving light-oxygenvoltage-sensing domains (LOV1 and LOV2) and a kinase domain. BL-excitedLOV2is thought to be primarily responsible for the BL-dependent activation of the kinase. However, the molecular mechanisms by which small BL-induced conformational changes in the LOV2 domain are transmitted to the kinase remain unclear. Here, we used full-length wild-type and mutant phot2 proteins from Arabidopsis to study their molecular properties in the dark and under BL irradiation. Phosphorylation assays and absorption measurements indicated that the LOV1 domain assists the thermal relaxation of BL-excited LOV2 and vice versa. Using small-angle X-ray scattering and electron microscopy, we observed that phot2 forms a dimer and has a rod shape with a maximum length of 188A° and a radius of gyration of 44 A°. Under BL, phot2 displayed large conformational changes that bent the rod shape. By superimposing the crystal structures of the LOV1 dimer, LOV2, and a homology model of the kinase to the observed changes, we inferred that the BL-dependent change consisted of positional shifts of both LOV2 and the kinase relative to LOV1. Furthermore, phot2 mutants lacking the photocycle in LOV1 or LOV2 still exhibited conformational changes under BL, suggesting that LOV1 and LOV2 cooperatively contribute to the conformational changes that activate the kinase. These results suggest that BL-activated LOV1 contributes to the kinase activity of phot2. We discuss the possible intramolecular interactions and signaling mechanisms in phot2. [ABSTRACT FROM AUTHOR]

Phytochrome B (phyB) is the primary red light photoreceptor in plants, and regulates both growth and development. The relative levels of phyB in the active state are determined by the light conditions, such as direct sunlight or shade, but are also affected by light-independent dark reversion. Dark reversion is a temperature-dependent thermal relaxation process, by which phyB reverts from the active to the inactive state. Here, we show that the homologous phyB-binding proteins PCH1 and PCHL suppress phyB dark reversion, resulting in plants with dramatically enhanced light sensitivity. Moreover, far-red and blue light upregulate the expression of PCH1 and PCHL in a phyB independent manner, thereby increasing the response to red light perceived by phyB. PCH1 and PCHL therefore provide a node for the molecular integration of different light qualities by regulation of phyB dark reversion, allowing plants to adapt growth and development to the ambient environment. [ABSTRACT FROM AUTHOR]

Light-induced chloroplast movement is found in most plant species, including algae and land plants. In land plants with multiple small chloroplasts, under weak light conditions, the chloroplasts move towards the light and accumulate on the periclinal cell walls to efficiently perceive light for photosynthesis (the accumulation response). Under strong light conditions, chloroplasts escape from light to avoid photodamage (the avoidance response). In most plant species, blue light induces chloroplast movement, and phototropin receptor kinases are the blue light receptors. Molecular mechanisms for photoreceptors, signal transduction and chloroplast motility systems are being studied using the model plant Arabidopsis thaliana. However, to further understand the molecular mechanisms and evolutionary history of chloroplast movement in green plants, analyses using other plant systems are required. Here, we review recent works on chloroplast movement in green algae, liverwort, mosses and ferns that provide new insights on chloroplast movement. [ABSTRACT FROM AUTHOR]

The phenotypes associated with plant photomorphogenesis such as the suppressed shade avoidance response and de-etiolation offer the potential for significant enhancement of crop yields. Of many light signal transducers and transcription factors involved in the photomorphogenic responses of plants, this review focuses on the transgenic overexpression of the photoreceptor genes at the uppermost stream of the signalling events, particularly phytochromes, crytochromes and phototropins as the transgenes for the genetic engineering of crops with improved harvest yields. In promoting the harvest yields of crops, the photoreceptors mediate the light regulation of photosynthetically important genes, and the improved yields often come with the tolerance to abiotic stresses such as drought, salinity and heavy metal ions. As a genetic engineering approach, the term photo-biotechnology has been coined to convey the idea that the greater the photosynthetic efficiency that crop plants can be engineered to possess, the stronger the resistance to biotic and abiotic stresses. Development of GM crops based on photoreceptor transgenes (mainly phytochromes, crytochromes and phototropins) is reviewed with the proposal of photo-biotechnology that the photoreceptors mediate the light regulation of photosynthetically important genes, and the improved yields often come with the added benefits of crops' tolerance to environmental stresses. [ABSTRACT FROM AUTHOR]

Plant photomorphogenesis is a complex of developmental and growth processes of light-mediated changes in plant morphology and structure, ontogenetic patterns as well as movements of plants, plant parts and/or organelles. During photomorphogenesis, plants respond to the quality, intensity and/or direction of radiation, to which they are exposed, by changes in plant development, growth and/or movement. This is a completely separate process from photosynthesis where light is used as a source of energy and for building of plant biomass, while in photomorphogenesis radiation plays a role of a signal. Photomorphogenesis is mediated by a sophisticated network of photoreceptors, which can be responsive to different kind of radiation and interfere in their action on plant photomorphogenetic processes. The most important families of photoreceptors are: 1) phytochromes sensing particularly in red visible light and being crucial in numerous photomorphogenetic processes; 2) cryptochromes, phototropins and recently discovered ZTL/FKF1/LKP2 proteins sense blue light and UV-A, while 3) very recently discovered UVR8 receptor percieve UV-B radiation. These photoreceptors interact in accord to orchestrate numerous developmental and physiological processes, e.g. germination, deetiolization, shade avoidance, phototropism, leaf development, flowering, movement of chloroplasts, to optimize their location in order to perceive the optimum irradiance, etc. . Due to photoreceptors, plants perceive their neighbours and can avoid shading by them through photomorphogenetic processes. In artificial greenhouse cultivation systems, it is possible to efficiently manipulate artificial radiation in order to optimize quality and quantity of plant biomass and yield. Nowadays, due to technological progress it is possible to cultivate plants not only in winter but also in polar regions during polar night. We can also manipulate radiation quality (e.g. using LED lighting), to induce better plant resistance to both abiotic factors such as drought, herbivores or pathogens. Also we can positively affect yield quality, e.g. to lower nitrates or increase anthocyanins in yield biomass. In addition, we can affect timing of flowering, seed germination etc. Photomorphogenesis is only marginally covered by all available Czech textbooks for high schools if at all and no practical experimental protocols are included. In the present paper we describe radiation sensing by plants via photoreceptors, give basic overview of photomorphogenetic processes and demonstrate a possible use of photomorphogenetic processes in agricultural and horticultural practice. In the subsequent paper/s we will describe selected photomorphogenetic processes in more detail giving the background to protocols for specific photomorphogenetic experiments. [ABSTRACT FROM AUTHOR]

Freshwater algae living in shallow waters have evolved various photomovement to stay in the optimum light condition for survival. Previous action-spectra investigations showed that Spirogyra filaments have phototropic movement in blue light. To decipher the genetic control of phototropic movement, two phototropin homologues were isolated from Spirogyra varians, and named SvphotA and SvphotB. Both phototropins have similar molecular structure consisted of two light-oxygen-voltage domains (LOV1, LOV2) and a serine / threonine kinase domain. SvphotA and SvphotB had 48.7% sequence identity. Phylogenetic analysis showed SvphotA and SvphotB belong to different clades suggesting early divergence, possibly before the divergence of land plants from the Zygnematales. Quantitative PCR and northern blot analysis showed that SvphotA and SvphotB responded differently to red and blue light. SvphotA was consistently expressed in the dark and in blue light, while SvphotB was expressed only when the plants were exposed to light. When the filaments were exposed to red light, SvphotA was significantly downregulated whereas SvphotB was highly upregulated. These results suggest that the two phototropins may have different roles in the photoresponse in S. varians. [ABSTRACT FROM AUTHOR]

Living organisms detect changes in temperature using thermosensory molecules. However, these molecules and/or their mechanisms for sensing temperature differ among organisms. To identify thermosensory molecules in plants, we investigated chloroplast positioning in response to temperature changes and identified a blue-light photoreceptor, phototropin, that is an essential regulator of chloroplast positioning. Based on the biochemical properties of phototropin during the cellular response to light and temperature changes, we found that phototropin perceives temperature based on the temperature-dependent lifetime of the photoactivated chromophore. Our findings indicate that phototropin perceives both blue light and temperature and uses this information to arrange the chloroplasts for optimal photosynthesis. Because the photoactivated chromophore of many photoreceptors has a temperature-dependent lifetime, a similar temperature-sensing mechanism likely exists in other organisms. Thus, photoreceptors may have the potential to function as thermoreceptors. [ABSTRACT FROM AUTHOR]

Phototropins (phots) are plasma membrane-associated serine/threonine kinases that coordinate a range of processes linked to optimizing photosynthetic efficiency in plants. These photoreceptors contain two light-, oxygen-, or voltage-sensing (LOV) domains within their N terminus, with each binding one molecule of flavin mononucleotide as a UV/blue light-absorbing chromophore. Although phots contain two LOV domains, light-induced activation of the C-terminal kinase domain and subsequent receptor autophosphorylation is controlled primarily by the A′α-LOV2-Jα photosensory module. Mutations that disrupt interactions between the LOV2 core and its flanking helical segments can uncouple this mode of light regulation. However, the impact of these mutations on phot function in Arabidopsis has not been explored. Here we report that histidine substitution of Arg-472 located within the A′α-helix of Arabidopsis phot1 constitutively activates phot1 kinase activity in vitro without affecting LOV2 photochemistry. Expression analysis of phot1 R472H in the phot-deficient mutant confirmed that it is autophosphorylated in darkness in vivo but unable to initiate phot1 signaling in the absence of light. Instead, we found that phot1 R472H is poorly functional under low-light conditions but can restore phototropism, chloroplast accumulation, stomatal opening, and leaf positioning and expansion at higher light intensities. Our findings suggest that Arabidopsis can adapt to the elevated phosphorylation status of the phot1 R472H mutant in part by reducing its stability, whereas the activity of the mutant under high-light conditions can be attributed to additional increases in LOV2-mediated photoreceptor autophosphorylation. [ABSTRACT FROM AUTHOR]

Chloroplast photorelocation movement, well-characterized light-induced response found in various plant species from alga to higher plants, is an important phenomenon for plants to increase photosynthesis efficiency and avoid photodamage. The signal for chloroplast accumulation movement connecting the blue light receptor, phototropin, and chloroplasts remains to be identified, although the photoreceptors and the mechanism of movement via chloroplast actin filaments have now been revealed in land plants. The characteristics of the signal have been found; the speed of signal transfer is about 1 µm min and that the signal for the accumulation response has a longer life and is transferred a longer distance than that of the avoidance response. Here, to collect the clues of the unknown signal substances, we studied the effect of temperature on the speed of signal transmission using the fern Adiantum capillus-veneris and found the possibility that the mechanism of signal transfer was not dependent on the simple diffusion of a substance; thus, some chemical reaction must also be involved. We also found new insights of signaling substances, such that microtubules are not involved in the signal transmission, and that the signal could even be transmitted through the narrow space between chloroplasts and the plasma membrane. [ABSTRACT FROM AUTHOR]

Chloroplast movement is induced by blue light in a broad range of plant species. Weak light induces the chloroplast accumulation response and strong light induces the chloroplast avoidance response. Both responses are essential for efficient photosynthesis and are mediated by phototropin blue-light receptors. J-DOMAIN PROTEIN REQUIRED FOR CHLOROPLAST ACCUMULATION RESPONSE 1 (JAC1) and two coiled-coil domain proteins WEAK CHLOROPLAST MOVEMENT UNDER BLUE LIGHT 1 (WEB1) and PLASTID MOVEMENT IMPAIRED 2 (PMI2) are required for phototropin-mediated chloroplast movement. Genetic analysis suggests that JAC1 is essential for the accumulation response and WEB1/PMI2 inhibit the accumulation response through the suppression of JAC1 activity under the strong light. We recently identified two phototropin-interacting proteins, ROOT PHOTOTROPISM 2 (RPT2) and NPH3/RPT2-like (NRL) PROTEIN FOR CHLOROPLAST MOVEMENT 1 (NCH1) as the signaling components involved in chloroplast accumulation response. However, the relationship between RPT2/NCH1, JAC1 and WEB1/PMI2 remained to be determined. Here, we performed genetic analysis between RPT2/NCH1, JAC1, and WEB1/PMI2 to elucidate the signal transduction pathway. [ABSTRACT FROM AUTHOR]

Phototropins (phots) are blue light sensors found in a variety of higher plants and algae. The photochemical reactions of this family of proteins have attracted much attention since their discovery. Phots have two light sensor domains called light-oxygen-voltage 1 (LOV1) and LOV2. After the formation of the characteristic adduct of the LOV domain, a conformational change of the C-terminal region of the LOV2 domain occurs, and characterizing this change is important for understanding biological function, that is, kinase activation. Here, the reaction dynamics of the Jα-helix and the extended region adjacent to the Jα-helix (connector) have been investigated. The conformation of the connector part and the Jα-helix were found to alter significantly in a two-state manner. Furthermore, the conformational change of the kinase domain was also successfully detected as a change in translational diffusion, although the CD intensity due to the kinase domain movement was almost silent. These observations indicate that the tertiary structure of the kinase domain changes. The rate of the kinase domain change is almost the same as that of the change for the LOV2-linker, suggesting that the conformational change of the linker is the rate-determining step for kinase activation. [ABSTRACT FROM AUTHOR]