Blue light signaling through the cryptochromes and phototropins. So that's what the blues is all about

Enhanced Solid-State Fluorescence of Flavin Derivatives by Incorporation in the Metal-Organic Frameworks MIL-53(Al) and MOF-5

The flavin derivatives 10-methyl-isoalloxazine (MIA) and 6-fluoro-10-methyl-isoalloxazine (6F-MIA) were incorporated in two alternative metal-organic frameworks, (MOFs) MIL-53(Al) and MOF-5. We used a post-synthetic, diffusion-based incorporation into microcrystalline MIL-53 powders with one-dimensional (1D) pores and an in-situ approach during the synthesis of MOF-5 with its 3D channel network. The maximum amount of flavin dye incorporation is 3.9 wt% for MIA@MIL-53(Al) and 1.5 wt% for 6F-MIA@MIL-53(Al), 0.85 wt% for MIA@MOF-5 and 5.2 wt% for 6F-MIA@MOF-5. For the high incorporation yields the probability to have more than one dye molecule in a pore volume is significant. As compared to the flavins in solution, the fluorescence spectrum of these flavin@MOF composites is broadened at the bathocromic side especially for MIA. Time-resolved spectroscopy showed that multi-exponential fluorescence lifetimes were needed to describe the decays. The fluorescence-weighted lifetime of flavin@MOF of 4 ± 1 ns also corresponds to those in solution but is significantly prolonged compared to the solid flavin dyes with less than 1 ns, thereby confirming the concept of "solid solutions" for dye@MOF composites. The fluorescence quantum yield (Φ_F) of the flavin@MOF composites is about half of the solution but is significantly higher compared to the solid flavin dyes. Both the fluorescence lifetime and quantum yield of flavin@MOF decrease with the flavin loading in MIL-53 due to the formation of various J-aggregates. Theoretical calculations using plane-wave and QM/MM methods are in good correspondence with the experimental results and explain the electronic structures as well as the photophysical properties of crystalline MIA and the flavin@MOF composites. In the solid flavins, π-stacking interactions of the molecules lead to a charge transfer state with low oscillator strength resulting in aggregation-caused quenching (ACQ) with low lifetimes and quantum yields. In the MOF pores, single flavin molecules represent a major population and the computed MIA@MOF structures do not find π-stacking interactions with the pore walls but only weak van-der-Waals contacts which reasons the enhanced fluorescence lifetime and quantum yield of the flavins in the composites compared to their neat solid state. To analyze the orientation of flavins in MOFs, we measured fluorescence anisotropy images of single flavin@MOF-5 crystals and a static ensemble flavin@MIL53 microcrystals, respectively. Based on image information, anisotropy distributions and overall curve of the time-resolved anisotropy curves combined with theoretical calculations, we can prove that all fluorescent flavins species have a defined and rather homogeneous orientation in the MOF framework. In MIL-53, the transition dipole moments of flavins are orientated along the 1D channel axis, whereas in MOF-5 we resolved an average orientation that is tilted with respect to the cubic crystal lattice. Notably, the more hydrophobic 6F-MIA exhibits a higher degree order than MIA. The flexible MOF MIL-53(Al) was optimized essentially to the experimental large-pore form in the guest-free state with QuantumEspresso (QE) and with MIA molecules in the pores the structure contracted to close to the experimental narrow-pore form which was also confirmed by PXRD. In summary, the incorporation of flavins in MOFs yields solid-state materials with enhanced rigidity, stabilized conformation, defined orientation and reduced aggregations of the flavins, leading to increased fluorescence lifetime and quantum yield as controllable photo-luminescent and photo-physical properties.

Expression Analysis and Interaction Protein Screening of CRY1 in Strawberry

Cryptochrome 1 (CRY1), a main blue light receptor protein, plays a significant role in several biological processes. However, the expression patterns and function of CRY1 in strawberry have not been identified. Here, the expression profile of CRY1 in different tissues and developmental stages of strawberry fruit, and expression patterns response to abiotic stresses (low temperature, salt and drought) were analyzed. Its subcellular localization, interaction proteins and heterologous overexpression in tobacco were also investigated. The results showed that CRY1 was mainly expressed in leaves and fruits with an expression peak at the initial red stage in strawberry fruit. Abiotic stresses could significantly induce the expression of CRY1. The CRY1 protein was located in both nucleus and cytoplasm. Five proteins (CSN5a-like, JAZ5, eIF3G. NF-YC9, and NDUFB9) interacting with CRY1 were discovered. Genes related flowering times, such as HY5 and CO, in three overexpressed FaCRY1 tobacco lines, were significantly upregulated. Taken together, our results suggested CRY1 have a broad role in biological processes in strawberry.

Molecular cloning of cryptochrome 1 from Lilium×formolongi and the characterization of its photoperiodic flowering function in Arabidopsis

Lilium × formolongi is an important cut flower species that is able to flower within a year following seed propagation, with flower induction that is very sensitive to the photoperiod. Cryptochromes are blue/UV-A light receptors that regulate many important plant growth and development processes, including photoperiodic flowering. In this study, we isolated the cryptochrome 1 (CRY1) gene from L. × formolongi and analyzed its function in transgenic Arabidopsis. The predicted LfCRY1 protein was strongly homologous to other CRY1 proteins. The transcription of LfCRY1 was induced by blue light, with LfCRY1 exhibiting its highest expression and diurnal expression patterns during the flowering-induction stage under both long-day (LD) and short-day (SD) photoperiods. Overexpression of LfCRY1 in Arabidopsis promoted flowering under LDs but not SDs and inhibited hypocotyl elongation under blue light. The LfCRY1 protein was located in both the nucleus and cytoplasm. LfCRY1 interacted with the important flowering activator LfCOL9 in both yeast and onion cells. These results provide functional evidence for the role of LfCRY1 in controlling photoperiodic flowering under LDs and indicate that LfCRY1 may be a counterpart of AtCRY1. Understanding the role of LfCRY1 in photoperiodic flowering is beneficial for the molecular breeding of lilies with shorter vegetative stages.

Flowering process in soybean under water deficit conditions: A review on genetic aspects

Soybean is a key crop in many countries, being used from human food to the animal industry due to its nutritional properties. Financially, the grain chain moves large sums of money into the economy of producing countries. However, like other agricultural commodities around the world, it can have its final yield seriously compromised by abiotic environmental stressors, like drought. As flowers imply in pods and in grains inside it to minimize damages caused by water restriction, researchers have focused on understanding flowering-process related genes and their interactions. Here a review dedicated to the soybean flowering process and gene network involved in it is presented, describing gene interactions and how genes act in this complex mechanism, also ruled by environmental triggers such as day-light and circadian cycle. The objective was to gather information and insights on the soybean flowering process, aiming to provide knowledge useful to assist in the development of drought-tolerant soybean lines, minimizing losses due to delays or anticipation of flowering and, consequently, restraining financial and productivity losses.

Orientations and water dynamics of photoinduced secondary charge-separated states for magnetoreception by cryptochrome

In the biological magnetic compass, blue-light photoreceptor protein of cryptochrome is thought to conduct the sensing of the Earth's magnetic field by photoinduced sequential long-range charge-separation (CS) through a cascade of tryptophan residues, W_A(H), W_B(H) and W_C(H). Mechanism of generating the weak-field sensitive radical pair (RP) is poorly understood because geometries, electronic couplings and their modulations by molecular motion have not been investigated in the secondary CS states generated prior to the terminal RP states. In this study, water dynamics control of the electronic coupling is revealed to be a key concept for sensing the direction of weak magnetic field. Geometry and exchange coupling (singlet-triplet energy gap: 2J) of photoinduced secondary CS states composed of flavin adenine dinucleotide radical anion (FAD^-•) and radical cation W_B(H)^+• in the cryptochrome DASH from Xenopus laevis were clarified by time-resolved electron paramagnetic resonance. We found a time-dependent energetic disorder in 2J and was interpreted by a trap CS state capturing one reorientated water molecule at 120 K. Enhanced electron-tunneling by water-libration was revealed for the terminal charge-separation event at elevated temperature. This highlights importance of optimizing the electronic coupling for regulation of the anisotropic RP yield on the possible magnetic compass senses.

Perception of solar UV radiation by plants: photoreceptors and mechanisms

About 95% of the ultraviolet (UV) photons reaching the Earth's surface are UV-A (315-400 nm) photons. Plant responses to UV-A radiation have been less frequently studied than those to UV-B (280-315 nm) radiation. Most previous studies on UV-A radiation have used an unrealistic balance between UV-A, UV-B, and photosynthetically active radiation (PAR). Consequently, results from these studies are difficult to interpret from an ecological perspective, leaving an important gap in our understanding of the perception of solar UV radiation by plants. Previously, it was assumed UV-A/blue photoreceptors, cryptochromes and phototropins mediated photomorphogenic responses to UV-A radiation and "UV-B photoreceptor" UV RESISTANCE LOCUS 8 (UVR8) to UV-B radiation. However, our understanding of how UV-A radiation is perceived by plants has recently improved. Experiments using a realistic balance between UV-B, UV-A, and PAR have demonstrated that UVR8 can play a major role in the perception of both UV-B and short-wavelength UV-A (UV-Asw, 315 to ∼350 nm) radiation. These experiments also showed that UVR8 and cryptochromes jointly regulate gene expression through interactions that alter the relative sensitivity to UV-B, UV-A, and blue wavelengths. Negative feedback loops on the action of these photoreceptors can arise from gene expression, signaling crosstalk, and absorption of UV photons by phenolic metabolites. These interactions explain why exposure to blue light modulates photomorphogenic responses to UV-B and UV-Asw radiation. Future studies will need to distinguish between short and long wavelengths of UV-A radiation and to consider UVR8's role as a UV-B/UV-Asw photoreceptor in sunlight.

Functional analysis of a novel cryptochrome gene (GbCRY1) from Ginkgo biloba

Cryptochrome (CRY) is a blue light receptor that is widely distributed in animals, plants, and microorganisms. CRY as a coding gene of cryptochrome that regulates the organism gene expression and plays an important role in organism growth and development. In this study, we identified four photolyase/cryptochrome (PHR/CRY) members from the genome of Ginkgo biloba. Phylogenetic tree analysis showed that the Ginkgo PHR/CRY family members were closely related to Arabidopsis thaliana and Solanum lycopersicum. We isolated a cryptochrome gene, GbCRY1, from G. biloba and analyzed its structure and function. GbCRY1 shared high similarity with AtCRY1 from A. thaliana. GbCRY1 expression level was higher in stems and leaves and lower in roots, male strobili, female strobili. GbCRY1 expression level fluctuated periodically within 24 h, gradually increased in the dark, and decreased under blue light. The newly germinated ginkgo seedlings were cultured under dark, white light, and blue light conditions. The blue light normally induced photomorphogenesis of ginkgo seedlings, which included hypocotyl elongation inhibition, leaf expansion inhibition, and chlorophyll formation. Treating dark-adapted ginkgo leaves with blue light could induce stomatal opening. At the same time, blue light reduced the expression level of GbCRY1 in the process of inducing photomorphogenesis and stoma opening. Our results provide evidence that GbCRY1 expression is affected by space, circadian cycle and light, and also proves that GbCRY1 is related to ginkgo circadian clock, photomorphogenesis and stoma opening process.

Engineering Photosensory Modules of Non-Opsin-Based Optogenetic Actuators

Optogenetic (photo-responsive) actuators engineered from photoreceptors are widely used in various applications to study cell biology and tissue physiology. In the toolkit of optogenetic actuators, the key building blocks are genetically encodable light-sensitive proteins. Currently, most optogenetic photosensory modules are engineered from naturally-occurring photoreceptor proteins from bacteria, fungi, and plants. There is a growing demand for novel photosensory domains with improved optical properties and light-induced responses to satisfy the needs of a wider variety of studies in biological sciences. In this review, we focus on progress towards engineering of non-opsin-based photosensory domains, and their representative applications in cell biology and physiology. We summarize current knowledge of engineering of light-sensitive proteins including light-oxygen-voltage-sensing domain (LOV), cryptochrome (CRY2), phytochrome (PhyB and BphP), and fluorescent protein (FP)-based photosensitive domains (Dronpa and PhoCl).

Contributions of cryptochromes and phototropins to stomatal opening through the day

The UV-A/blue photoreceptors phototropins and cryptochromes are both known to contribute to stomatal opening (Δgs) in blue light. However, their relative contributions to the maintenance of gs in blue light through the whole photoperiod remain unknown. To elucidate this question, Arabidopsis phot1 phot2 and cry1 cry2 mutants (MTs) and their respective wild types (WTs) were irradiated with 200 μmolm-2s-1 of blue-, green- or red-light (BL, GL or RL) throughout a 11-h photoperiod. Stomatal conductance (gs) was higher under BL than under RL or GL. Under RL, gs was not affected by either of the photoreceptor mutations, but under GL gs was slightly lower in cry1 cry2 than its WT. Under BL, the presence of phototropins was essential for rapid stomatal opening at the beginning of the photoperiod, and maximal stomatal opening beyond 3 h of irradiation required both phototropins and cryptochromes. Time courses of whole-plant net carbon assimilation rate (Anet) and the effective quantum yield of PSII photochemistry (ΦPSII) were consistent with an Anet-independent contribution of BL on gs both in phot1 phot2 and cry1 cry2 mutants. The changing roles of phototropins and cryptochromes through the day may allow more flexible coordination between gs and Anet.

Light quality affects light harvesting and carbon sequestration during the diel cycle of crassulacean acid metabolism in Phalaenopsis

Crassulacean acid metabolism (CAM) is a specialized photosynthetic pathway present in a variety of genera including many epiphytic orchids. CAM is under circadian control and can be subdivided into four discrete phases during a diel cycle. Inherent to this specific mode of metabolism, carbohydrate availability is a limiting factor for nocturnal CO₂ uptake and biomass production. To evaluate the effects of light quality on the photosynthetic performance and diel changes in carbohydrates during the CAM cycle. Phalaenopsis plants were grown under four different light qualities (red, blue, red + blue and full spectrum white light) at a fluence of 100 µmol m^-2 s^-1 and a photoperiod of 12 h for 8 weeks. In contrast to monochromatic blue light, plants grown under monochromatic red light showed already a significant decline of the quantum efficiency (Φ_PSII) after 5 days and of the maximum quantum yield (F_v/F_m) after 10 days under this treatment. This was also reflected in a compromised chlorophyll and carotenoid content and total diel CO₂ uptake under red light in comparison with monochromatic blue and full spectrum white light. In particular, CO₂ uptake during nocturnal phase I was affected under red illumination resulting in a reduced amount of vacuolar malate. In addition, red light caused the rate of decarboxylation of malate during the day to be consistently lower and malic acid breakdown persisted until 4 h after dusk. Because the intrinsic activity of PEPC was not affected, the restricted availability of storage carbohydrates such as starch was likely to cause these adverse effects under red light. Addition of blue to the red light spectrum restored the diel fluxes of carbohydrates and malate and resulted in a significant enhancement of the daily CO₂ uptake, pigment concentration and biomass formation.

ClCRY2 facilitates floral transition in Chrysanthemum lavandulifolium by affecting the transcription of circadian clock-related genes under short-day photoperiods

Plants sense photoperiod signals to confirm the optimal flowering time. Previous studies have shown that Cryptochrome2 (CRY2) functions to promote floral transition in the long-day plant (LDP) Arabidopsis; however, the function and molecular mechanism by which CRY2 regulates floral transition in short-day plants (SDPs) is still unclear. In this study, we identified a CRY2 homologous gene, ClCRY2, from Chrysanthemum lavandulifolium, a typical SDP. The morphological changes in the C. lavandulifolium shoot apex and ClFTs expression analysis under SD conditions showed that adult C. lavandulifolium completed the developmental transition from vegetative growth to reproductive growth after eight SDs. Meanwhile, ClCRY2 mRNA exhibited an increasing trend from 0 to 8 d of SD treatment. ClCRY2 overexpression in wild-type (WT) Arabidopsis and C. lavandulifolium resulted in early flowering. The transcript levels of the CONSTANS-like (COL) genes ClCOL1, ClCOL4, and ClCOL5, and FLOWERING LOCUS T (FT) homologous gene ClFT1 were upregulated in ClCRY2 overexpression (ClCRY2-OE) C. lavandulifolium under SD conditions. The transcript levels of some circadian clock-related genes, including PSEUDO-REPONSE REGULATOR 5 (PRR5), ZEITLUPE (ZTL), FLAVIN-BINDING KELCH REPEAT F-BOX 1 (FKF1), and GIGANTEA (GI-1 and GI-2), were upregulated in ClCRY2-OE C. lavandulifolium, while the expression levels of other circadian clock-related genes, such as EARLY FLOWERING 3 (ELF3), ELF4, LATE ELONGATED HYPOCOTYL (LHY), PRR73, and REVEILLE8 (RVE8), were downregulated in ClCRY2-OE C. lavandulifolium under SD conditions. Taken together, the results suggest that ClCRY2 promotes floral transition by fine-tuning the expression of circadian clock-related gene, ClCOLs and ClFT1 in C. lavandulifolium under SD conditions.

Long-Term Effects of Red- and Blue-Light Emitting Diodes on Leaf Anatomy and Photosynthetic Efficiency of Three Ornamental Pot Plants

Light quality critically affects plant development and growth. Development of light-emitting diodes (LEDs) enables the use of narrow band red and/or blue wavelengths as supplementary lighting in ornamental production. Yet, long periods under these wavelengths will affect leaf morphology and physiology. Leaf anatomy, stomatal traits, and stomatal conductance, leaf hydraulic conductance (K_leaf), and photosynthetic efficiency were investigated in three ornamental pot plants, namely Cordyline australis (monocot), Ficus benjamina (dicot, evergreen leaves), and Sinningia speciosa (dicot, deciduous leaves) after 8 weeks under LED light. Four light treatments were applied at 100 μmol m^-2 s^-1 and a photoperiod of 16 h using 100% red (R), 100% blue (B), 75% red with 25% blue (RB), and full spectrum white light (W), respectively. B and RB resulted in a greater maximum quantum yield (F_v/F_m) and quantum efficiency (Φ_PSII) in all species compared to R and W and this correlated with a lower biomass under R. B increased the stomatal conductance compared with R. This increase was linked to an increasing stomatal index and/or stomatal density but the stomatal aperture area was unaffected by the applied light quality. Leaf hydraulic conductance (K_leaf) was not significantly affected by the applied light qualities. Blue light increased the leaf thickness of F. benjamina, and a relative higher increase in palisade parenchyma was observed. Also in S. speciosa, increase in palisade parenchyma was found under B and RB, though total leaf thickness was not affected. Palisade parenchyma tissue thickness was correlated to the leaf photosynthetic quantum efficiency (Φ_PSII). In conclusion, the role of blue light addition in the spectrum is essential for the normal anatomical leaf development which also impacts the photosynthetic efficiency in the three studied species.

Novel insight into the mechanism underlying light-controlled anthocyanin accumulation in eggplant (Solanum melongena L.)

Eggplant is rich in anthocyanins, which are the major secondary metabolites and beneficial to human health. We discovered that the anthocyanin biosynthesis of eggplant cultivar 'Lanshan Hexian' was regulated by light. In this study, we isolated two blue light receptor genes, SmCRY1 and SmCRY2, and negative/positive anthocyanin regulatory factors SmCOP1 and SmHY5 from eggplant. In terms of transcript levels, SmCRY1, SmCRY2 and SmHY5 were up-regulated by light, while SmCOP1 was down-regulated. Subsequently, the four genes were functionally complemented in phenotype of corresponding mutants, indicating that they act as counterparts of Arabidopsis genes. Yeast two-hybrid and bimolecular fluorescence complementation assays showed that SmCRY1 and SmCRY2 interact with SmCOP1 in a blue-light-dependent manner. It also obtained the result that SmCOP1 interacts with SmHY5 and SmMYB1. Furthermore, using yeast one-hybrid assay, we found that SmHY5 and SmMYB1 both bind the promoters of anthocyanin biosynthesis structural genes (SmCHS and SmDFR). Taken together, blue-light-triggered CRY1/CRY2-COP1 interaction creates the condition that HY5 and MYB1 combine with the downstream anthocyanin synthesis genes (CHS and DFR) in eggplant. Our finding provides a new working model by which light controls anthocyanin accumulation in eggplant.

Melatonin feedback on clock genes: a theory involving the proteasome

The expression of 'clock' genes occurs in all tissues, but especially in the suprachiasmatic nuclei (SCN) of the hypothalamus, groups of neurons in the brain that regulate circadian rhythms. Melatonin is secreted by the pineal gland in a circadian manner as influenced by the SCN. There is also considerable evidence that melatonin, in turn, acts on the SCN directly influencing the circadian 'clock' mechanisms. The most direct route by which melatonin could reach the SCN would be via the cerebrospinal fluid of the third ventricle. Melatonin could also reach the pars tuberalis (PT) of the pituitary, another melatonin-sensitive tissue, via this route. The major 'clock' genes include the period genes, Per1 and Per2, the cryptochrome genes, Cry1 and Cry2, the clock (circadian locomotor output cycles kaput) gene, and the Bmal1 (aryl hydrocarbon receptor nuclear translocator-like) gene. Clock and Bmal1 heterodimers act on E-box components of the promoters of the Per and Cry genes to stimulate transcription. A negative feedback loop between the cryptochrome proteins and the nucleus allows the Cry and Per proteins to regulate their own transcription. A cycle of ubiquitination and deubiquitination controls the levels of CRY protein degraded by the proteasome and, hence, the amount of protein available for feedback. Thus, it provides a post-translational component to the circadian clock mechanism. BMAL1 also stimulates transcription of REV-ERBα and, in turn, is also partially regulated by negative feedback by REV-ERBα. In the 'black widow' model of transcription, proteasomes destroy transcription factors that are needed only for a particular period of time. In the model proposed herein, the interaction of melatonin and the proteasome is required to adjust the SCN clock to changes in the environmental photoperiod. In particular, we predict that melatonin inhibition of the proteasome interferes with negative feedback loops (CRY/PER and REV-ERBα) on Bmal1 transcription genes in both the SCN and PT. Melatonin inhibition of the proteasome would also tend to stabilize BMAL1 protein itself in the SCN, particularly at night when melatonin is naturally elevated. Melatonin inhibition of the proteasome could account for the effects of melatonin on circadian rhythms associated with molecular timing genes. The interaction of melatonin with the proteasome in the hypothalamus also provides a model for explaining the dramatic 'time of day' effect of melatonin injections on reproductive status of seasonal breeders. Finally, the model predicts that a proteasome inhibitor such as bortezomib would modify circadian rhythms in a manner similar to melatonin.

Cryptochrome 1 regulates growth and development in Brassica through alteration in the expression of genes involved in light, phytohormone and stress signalling

The blue light photoreceptors cryptochromes are ubiquitous in higher plants and are vital for regulating plant growth and development. In spite of being involved in controlling agronomically important traits like plant height and flowering time, cryptochromes have not been extensively characterized from agriculturally important crops. Here we show that overexpression of CRY1 from Brassica napus (BnCRY1), an oilseed crop, results in short-statured Brassica transgenics, likely to be less prone to wind and water lodging. The overexpression of BnCRY1 accentuates the inhibition of cell elongation in hypocotyls of transgenic seedlings. The analysis of hypocotyl growth inhibition and anthocyanin accumulation responses in BnCRY1 overexpressors substantiates that regulation of seedling photomorphogenesis by cry1 is dependent on light intensity. This study highlights that the photoactivated cry1 acts through coordinated induction and suppression of specific downstream genes involved in phytohormone synthesis or signalling, and those involved in cell wall modification, during de-etiolation of Brassica seedlings. The microarray-based transcriptome profiling also suggests that the overexpression of BnCRY1 alters abiotic/biotic stress signalling pathways; the transgenic seedlings were apparently oversensitive to abscisic acid (ABA) and mannitol.

Molecular cloning of cryptochrome 1 from apple and its functional characterization in Arabidopsis

Cryptochromes are blue-light photoreceptors involved in regulating many aspects of plant growth and development. Investigations of cryptochromes in plants have largely focused on Arabidopsis (Arabidopsis thaliana), tomato (Solanum lycopersicum), rice (Oryza sativa) and pea (Pisum sativum). Here, we isolated the cryptochrome 1 gene from apple (Malus domestica) (MdCRY1) and analyzed its function in transgenic Arabidopsis. The predicted MdCRY1 protein was most closely homologous to strawberry CRY1. In terms of transcript levels, MdCRY1 expression was up-regulated by light. The function of MdCRY1 was analyzed through heterologous expression in Arabidopsis. Overexpression of MdCRY1 in Arabidopsis is able to rescue the cry1 mutant phenotype, inhibit hypocotyl elongation, promote root growth, and enhance anthocyanin accumulation in wild-type seedlings under blue light. These data provide functional evidence for a role of MdCRY1 in controlling photomorphogenesis under blue light and indicate that CRY1 function is conserved between Arabidopsis and apple. Furthermore, we found that MdCRY1 interacts with AtCOP1 in both yeast and onion cells. This interaction may represent an important regulatory mechanism in blue-light signaling pathway in apple.

Blue-light-receptive cryptochrome is expressed in a sponge eye lacking neurons and opsin

Many larval sponges possess pigment ring eyes that apparently mediate phototactic swimming. Yet sponges are not known to possess nervous systems or opsin genes, so the unknown molecular components of sponge phototaxis must differ fundamentally from those in other animals, inspiring questions about how this sensory system functions. Here we present molecular and biochemical data on cryptochrome, a candidate gene for functional involvement in sponge pigment ring eyes. We report that Amphimedon queenslandica, a demosponge, possesses two cryptochrome/photolyase genes, Aq-Cry1 and Aq-Cry2. The mRNA of one gene (Aq-Cry2) is expressed in situ at the pigment ring eye. Additionally, we report that Aq-Cry2 lacks photolyase activity and contains a flavin-based co-factor that is responsive to wavelengths of light that also mediate larval photic behavior. These results suggest that Aq-Cry2 may act in the aneural, opsin-less phototaxic behavior of a sponge.

Comparative genomic analysis of soybean flowering genes

Flowering is an important agronomic trait that determines crop yield. Soybean is a major oilseed legume crop used for human and animal feed. Legumes have unique vegetative and floral complexities. Our understanding of the molecular basis of flower initiation and development in legumes is limited. Here, we address this by using a computational approach to examine flowering regulatory genes in the soybean genome in comparison to the most studied model plant, Arabidopsis. For this comparison, a genome-wide analysis of orthologue groups was performed, followed by an in silico gene expression analysis of the identified soybean flowering genes. Phylogenetic analyses of the gene families highlighted the evolutionary relationships among these candidates. Our study identified key flowering genes in soybean and indicates that the vernalisation and the ambient-temperature pathways seem to be the most variant in soybean. A comparison of the orthologue groups containing flowering genes indicated that, on average, each Arabidopsis flowering gene has 2-3 orthologous copies in soybean. Our analysis highlighted that the CDF3, VRN1, SVP, AP3 and PIF3 genes are paralogue-rich genes in soybean. Furthermore, the genome mapping of the soybean flowering genes showed that these genes are scattered randomly across the genome. A paralogue comparison indicated that the soybean genes comprising the largest orthologue group are clustered in a 1.4 Mb region on chromosome 16 of soybean. Furthermore, a comparison with the undomesticated soybean (Glycine soja) revealed that there are hundreds of SNPs that are associated with putative soybean flowering genes and that there are structural variants that may affect the genes of the light-signalling and ambient-temperature pathways in soybean. Our study provides a framework for the soybean flowering pathway and insights into the relationship and evolution of flowering genes between a short-day soybean and the long-day plant, Arabidopsis.

AUXIN-BINDING-PROTEIN1, the second auxin receptor: what is the significance of a two-receptor concept in plant signal transduction?

Since we are living in the 'age of transcription', awareness of aspects other than transcription in auxin signal transduction seems to have faded. One purpose of this review is to recall these other aspects. The focus will also be on the time scales of auxin responses and their potential or known dependence on either AUXIN BINDING PROTEIN 1 (ABP1) or on TRANSPORT-INHIBITOR-RESISTANT1 (TIR1) as a receptor. Furthermore, both direct and indirect evidence for the function of ABP1 as a receptor will be reviewed. Finally, the potential functions of a two-receptor system for auxin and similarities to other two-receptor signalling systems in plants will be discussed. It is suggested that such a functional arrangement is a property of plants which strengthens tissue autonomy and overcomes the lack of nerves or blood circulation which are responsible for rapid signal transport in animals.

Response of mitochondrial alternative oxidase (AOX) to light signals

Mitochondrial alternative oxidase (AOX), the unique respiratory terminal oxidase in plants, catalyzes the energy wasteful cyanide (CN)-resistant respiration and plays a role in optimizing photosynthesis. Recent studies from our group indicated that AOX plays a crucial role in chloroplast protection under extreme environments, such as high light (HL). Genetic data suggest that AOX is upregulated by light that was mediated by photoreceptors (phytochromes, phototropins and cryptochromes), and it also might have a particular role in relieving the overreduction of chloroplasts. Physiological analyses further suggest that AOX is essential for the dark-to-light transition, especially in de-etiolation course. In this mini-review, we highlight recent progresses in understanding the beneficial interaction between photosynthesis and mitochondria metabolism and discuss the possible role and mechanism of AOX in dissipation of excess reduced equivalents for chloroplasts under high light condition.

ROOT UV-B SENSITIVE2 acts with ROOT UV-B SENSITIVE1 in a root ultraviolet B-sensing pathway

Ultraviolet B light (UV-B; 280-320 nm) perception and signaling are well-known phenomena in plants, although no specific UV-B photoreceptors have yet been identified. We previously reported on the root UV-B sensitive1 (rus1) mutants in Arabidopsis (Arabidopsis thaliana), which display a block to development under very-low-fluence-rate UV-B (<0.1 mumol m(-2) s(-1)) after the seedling emerges from the seed. Here, we report the analysis and cloning of the rus2-1 mutation in Arabidopsis. The phenotype of rus2-1 mutant seedlings is virtually indistinguishable from the phenotype of rus1 seedlings. A map-based approach was used to clone RUS2. RUS2 encodes a domain of unknown function (DUF647)-containing protein that is homologous to the RUS1 protein. rus1-2 rus2-1 double mutant seedlings have the same phenotype as both rus1 and rus2 single mutants, suggesting that the two genes work in the same pathway. RUS2-Green Fluorescent Protein shows a similar expression pattern as that of RUS1-Green Fluorescent Protein, and RUS1 and RUS2 proteins interact physically in yeast. This protein-protein interaction depends on the DUF647 domain, and site-directed mutagenesis identified specific residues in DUF647 that are required for both protein-protein interaction and physiological function. Six RUS genes are found in Arabidopsis, rice (Oryza sativa), and moss (Physcomitrella patens), and one RUS member, RUS3, is conserved in plants and animals. Our results demonstrate that RUS2 works with RUS1 in a root UV-B-sensing pathway that plays a vital role in Arabidopsis early seedling morphogenesis and development.

Preparation and analysis of an expressed sequence tag library from the toxic dinoflagellate Alexandrium catenella

Dinoflagellates of the genus Alexandrium are photosynthetic microalgae that have an extreme importance due to the impact of some toxic species on shellfish aquaculture industry. Alexandrium catenella is the species responsible for the production of paralytic shellfish poisoning in Chile and other geographical areas. We have constructed a cDNA library from midexponential cells of A. catenella grown in culture free of associated bacteria and sequenced 10,850 expressed sequence tags (ESTs) that were assembled into 1,021 contigs and 5,475 singletons for a total of 6,496 unigenes. Approximately 41.6% of the unigenes showed similarity to genes with predicted function. A significant number of unigenes showed similarity with genes from other dinoflagellates, plants, and other protists. Among the identified genes, the most expressed correspond to those coding for proteins of luminescence, carbohydrate metabolism, and photosynthesis. The sequences of 9,847 ESTs have been deposited in Gene Bank (accession numbers EX 454357-464203).

The AT-hook-containing proteins SOB3/AHL29 and ESC/AHL27 are negative modulators of hypocotyl growth in Arabidopsis

SOB3, which encodes a plant-specific AT-hook motif containing protein, was identified from an activation-tagging screen for suppressors of the long-hypocotyl phenotype of a weak phyB allele, phyB-4. sob3-D (suppressor of phyB-4#3 dominant) overexpressing seedlings have shorter hypocotyls, and as adults develop larger flowers and leaves, and are delayed in senescence compared with wild-type plants. At the nucleotide level, SOB3 is closely related to ESCAROLA (ESC), which was identified in an independent activation-tagging screen. ESC overexpression also suppresses the phyB-4 long-hypocotyl phenotype, and confers an adult morphology similar to sob3-D, suggesting similar functions. Analysis of transgenic plants harboring SOB3:SOB3-GUS or ESC:ESC-GUS translational fusions, driven by their endogenous promoter regions, showed GUS activity in the hypocotyl and vasculature tissue in light- and dark-grown seedlings. A loss-of-function SOB3 allele (sob3-4) was generated through an ethyl methanesulfonate intragenic suppressor screen of sob3-D phyB-4 plants, and this allele was combined with a predicted null allele, disrupting ESC (esc-8), to examine potential genetic interactions. The sob3-4 esc-8 double mutant had a long hypocotyl in multiple fluence rates of continuous white, far-red, red and blue light. sob3-4 esc-8 phyB-9 and sob3-4 esc-8 cry-103 triple mutants also had longer hypocotyls than photoreceptor single mutants. In contrast, the sob3-4 esc-8 phyA-211 triple mutant was the same length as phyA-211 single mutants. Taken together, these data indicate that SOB3 and ESC act redundantly to modulate hypocotyl growth inhibition in response to light.

Glutathione S-transferase interacting with far-red insensitive 219 is involved in phytochrome A-mediated signaling in Arabidopsis

Far-red (FR) insensitive 219 (FIN219) was previously shown to be involved in phytochrome A-mediated FR light signaling. To further understand its function and regulatory relation with other light-signaling components, a yeast two-hybrid approach was used to isolate FIN219-interacting partners. Here, we demonstrate that FIN219-interacting protein 1 (FIP1) interacts with FIN219 in vitro and in vivo and is composed of 217 amino acids that belong to the tau class of the large glutathione S-transferase gene family. FIP1 was further shown to have glutathione S-transferase activity. The gain of function and partial loss of function of FIP1 resulted in a hyposensitive hypocotyl phenotype under continuous FR (cFR) light and a delayed flowering phenotype under long-day conditions, which suggests that FIP1 may exist in a complex to function in the regulation of Arabidopsis (Arabidopsis thaliana) development. In addition, FIP1 mRNA was down-regulated in the suppressor of phytochrome A-105 1 mutant and differentially expressed in constitutive photomorphogenic 1-4 (cop1-4) and cop1-5 mutants under cFR. Intriguingly, FIP1 expression was up-regulated in the fin219 mutant under all light conditions, except cFR. Furthermore, promoter activity assays revealed that FIP1 expression was light dependent, mainly associated with vascular tissues, and developmentally regulated. Subcellular localization studies revealed that the beta-glucuronidase-FIP1 fusion protein was localized in the nucleus and cytoplasm. Taken together, these data indicate that FIP1 may interact with FIN219 to regulate cell elongation and flowering in response to light.

Protein phosphatase 1 positively regulates stomatal opening in response to blue light in Vicia faba

Phototropins, plant blue light receptors, mediate stomatal opening through the activation of the plasma membrane H(+)-ATPase by unknown mechanisms. Here we report that type 1 protein phosphatase (PP1) positively regulates the blue light signaling between phototropins and the H(+)-ATPase in guard cells of Vicia faba. We cloned the four catalytic subunits of PP1 (PP1c) from guard cells and determined the expression of the isoforms in various tissues. Transformation of Vicia guard cells with PP1c isoforms that had lost enzymatic activity by one amino acid mutation, or with human inhibitor-2, a specific inhibitor protein of PP1c, suppressed blue light-induced stomatal opening. Addition of fusicoccin, an activator of the plasma membrane H(+)-ATPase, to these transformed guard cells induced normal stomatal opening, suggesting that the transformations did not affect the basic mechanisms for stomatal opening. Tautomycin, an inhibitor of PP1, inhibited blue light-induced H(+) pumping, phosphorylation of the plasma membrane H(+)-ATPase in guard cell protoplasts, and stomatal opening. However, tautomycin did not inhibit the blue light-dependent phosphorylation of phototropins. We conclude that PP1 functions downstream of phototropins and upstream of the H(+)-ATPase in the blue light signaling pathway of guard cells.

A role for ethylene in the phytochrome-mediated control of vegetative development

Members of the phytochrome family of photoreceptors play key roles in vegetative plant development, including the regulation of stem elongation, leaf development and chlorophyll accumulation. Hormones have been implicated in the control of these processes in de-etiolating seedlings. However, the mechanisms by which the phytochromes regulate vegetative development in more mature plants are less well understood. Pea (Pisum sativum) mutant plants lacking phytochromes A and B, the two phytochromes present in this species, develop severe defects later in development, including short, thick, distorted internodes and reduced leaf expansion, chlorophyll content and CAB gene transcript level. Studies presented here indicate that many of these defects in phyA phyB mutant plants appear to be due to elevated ethylene production, and suggest that an important role of the phytochromes in pea is to restrict ethylene production to a level that does not inhibit vegetative growth. Mutant phyA phyB plants produce significantly more ethylene than WT plants, and application of an ethylene biosynthesis inhibitor rescued many aspects of the phyA phyB mutant phenotype. This deregulation of ethylene production in phy-deficient plants appears likely to be due, at least in part, to the elevated transcript levels of key ethylene-biosynthesis genes. The phytochrome A photoreceptor appears to play a prominent role in the regulation of ethylene production, as phyA, but not phyB, single-mutant plants also exhibit a phenotype consistent with elevated ethylene production. Potential interactions between ethylene and secondary plant hormones in the control of the phy-deficient mutant phenotype were explored, revealing that ethylene may inhibit stem elongation in part by reducing gibberellin levels.

Reversal by Green Light of Blue Light-stimulated Stomatal Opening in Intact, Attached Leaves of Arabidopsis Operates Only in the Potassium-dependent, Morning Phase of Movement

Green light reversal of blue light-stimulated stomatal opening was discovered in isolated stomata. The present study shows that the response also occurs in stomata from intact leaves. Arabidopsis thaliana plants were grown in a growth chamber under blue, red and green light. Removal of the green light opened the stomata and restoration of green light closed them to baseline values under experimental conditions that rule out a mesophyll-mediated effect. Assessment of the response to green light over a daily time course showed that the stomatal sensitivity to green light was observed only in the morning, which coincided with the use of potassium as a guard cell osmoticum. Sensitivity to green light was absent during the afternoon phase of stomatal movement, which was previously shown to be dominated by sucrose osmoregulation in Vicia faba. Hence, the shift away from potassium-based osmoregulation in guard cells is further postulated to entail a shift from blue light to photosynthesis as the primary component of the stomatal response to light. Stomata from intact leaves of the zeaxanthin-less, npq1 mutant of Arabidopsis failed to respond to the removal or restoration of green light in the growth chamber, or to short, high fluence pulses of blue or green light. These data confirm previous studies showing that npq1 stomata are devoid of a specific blue light response. In contrast, stomata from intact leaves of phot1 phot2 double mutant plants had a reduced but readily detectable response to the removal of green light and to blue and green pulses.

Conservation and divergence of light-regulated genome expression patterns during seedling development in rice and Arabidopsis

Genome-wide 70-mer oligonucleotide microarrays of rice (Oryza sativa) and Arabidopsis thaliana were used to profile genome expression changes during light-regulated seedling development. We estimate that the expression of approximately 20% of the genome in both rice and Arabidopsis seedlings is regulated by white light. Qualitatively similar expression profiles from seedlings grown under different light qualities were observed in both species; however, a quantitatively weaker effect on genome expression was observed in rice. Most metabolic pathways exhibited qualitatively similar light regulation in both species with a few species-specific differences. Global comparison of expression profiles between rice and Arabidopsis reciprocal best-matched gene pairs revealed a higher correlation of genome expression patterns in constant light than in darkness, suggesting that the genome expression profile of photomorphogenesis is more conserved. Transcription factor gene expression under constant light exposure was poorly conserved between the two species, implying a faster-evolving rate of transcription factor gene expression in light-grown plants. Organ-specific expression profiles during seedling photomorphogenesis provide genome-level evidence for divergent light effects in different higher plant organs. Finally, overrepresentation of specific promoter motifs in root- and leaf-specific light-regulated genes in both species suggests that these cis-elements are important for gene expression responses to light.

Cryptochrome 1 contributes to blue-light sensing in pea

Cryptochromes are widespread in higher plants but their physiological roles as blue-light photoreceptors have been examined in relatively few species. Screening in a phyA null mutant background has identified several blue-light response mutants in pea (Pisum sativum), including one that carries a substitution of a highly conserved glycine residue in the N-terminal photolyase-homologous domain of the pea CRY1 gene. Analyses of cry1, phyA, and phyB mutants show that all three photoreceptors contribute to seedling photomorphogenesis under high-irradiance blue light, whereas phyA is the main photoreceptor active under low irradiances. Triple phyA phyB cry1 mutants grown under high-irradiance blue light are indistinguishable from dark-grown wild-type plants in length and leaf expansion but show a small residual response to higher-irradiance white light. Monogenic cry1 mutants have little discernable phenotype at the seedling stage, but later in development are more elongated than wild-type plants. In addition, the loss of cry1 moderates the short-internode phenotype of older phyA mutants, suggesting an antagonism between phyA and cry1 under some conditions. Pea cry1 has a small inhibitory effect on flowering under long and short days. However, the phyA cry1 double mutant retains a clear promotion of flowering in response to blue-light photoperiod extensions, indicating a role for one or more additional blue-light photoreceptors in the control of flowering in pea.

COP1 - from plant photomorphogenesis to mammalian tumorigenesis

The COP1 (constitutive photomorphogenic 1) protein, comprising RING finger, coiled-coil and WD40 domains, is conserved in both higher plants and vertebrates. In plants, COP1 acts as an E3 ubiquitin ligase to repress light signaling by targeting photoreceptors and downstream transcription factors for ubiquitylation and degradation. The activity of COP1 in plant cells correlates with its cytoplasmic and nuclear partitioning according to dark or light conditions. In addition, various signaling molecules have been shown to directly interact with COP1 and modulate its activity. Recently, scientists have begun to probe the function and regulation of COP1 in mammalian systems. Initial studies have pointed at possible roles for mammalian COP1 in tumorigenesis and the stress response through regulating the activities of p53 and c-Jun.

Isolation and stomatal opening activity of two oxylipins from Ipomoea tricolor

Bioassay-guided fractionation of a 50% MeOH extract of Ipomoea tricolor enabled the isolation of two oxylipins, cis-12-oxophytodienoic acid (OPDA, 1) and a novel monogalactosylmonoacylglyceride (2) containing OPDA, that acted as inducers of stomatal opening. These oxylipins enhanced stomatal opening of Commelina communis in darkness at micromolar concentrations.

Form, function and environments of the early angiosperms: merging extant phylogeny and ecophysiology with fossils

The flowering plants--angiosperms--appeared during the Early Cretaceous period and within 10-30 Myr dominated the species composition of many floras worldwide. Emerging insights into the phylogenetics of development and discoveries of early angiosperm fossils are shedding increased light on the patterns and processes of early angiosperm evolution. However, we also need to integrate ecology, in particular how early angiosperms established a roothold in pre-existing Mesozoic plant communities. These events were critical in guiding subsequent waves of angiosperm diversification during the Aptian-Albian. Previous pictures of the early flowering plant ecology have been diverse, ranging from large tropical rainforest trees, weedy drought-adapted and colonizing shrubs, disturbance- and sun-loving rhizomatous herbs, and, more recently, aquatic herbs; however, none of these images were tethered to a robust hypothesis of angiosperm phylogeny. Here, we synthesize our current understanding of early angiosperm ecology, focusing on patterns of functional ecology, by merging recent molecular phylogenetic studies and functional studies on extant 'basal angiosperms' with the picture of early angiosperm evolution drawn by the fossil record.

Light signal transduction in higher plants

Plants utilize several families of photoreceptors to fine-tune growth and development over a large range of environmental conditions. The UV-A/blue light sensing phototropins mediate several light responses enabling optimization of photosynthetic yields. The initial event occurring upon photon capture is a conformational change of the photoreceptor that activates its protein kinase activity. The UV-A/blue light sensing cryptochromes and the red/far-red sensing phytochromes coordinately control seedling establishment, entrainment of the circadian clock, and the transition from vegetative to reproductive growth. In addition, the phytochromes control seed germination and shade-avoidance responses. The molecular mechanisms involved include light-regulated subcellular localization of the photoreceptors, a large reorganization of the transcriptional program, and light-regulated proteolytic degradation of several photoreceptors and signaling components.

The Evolution and Function of Blue and Red Light Photoreceptors

Photoreceptors allow living organisms to optimize perception of light in the natural environment and thus to gain information about their external world. In this review, we describe blue and red light photoreceptors in bacteria, plants, and animals in relation to their evolution. Analyses performed in different organisms have revealed wonderful examples of structural modifications of the light-sensing proteins themselves, as well as diversification of the signal transduction pathways they use in relation with their evolutionary history and function. In different organisms, the same photoreceptor may have a very conserved role (convergent evolution of function) or may modulate different responses (acquisition of new function). Multiple photoreceptors of the same family in the same organism indicate gene duplication events during evolution, with a consequent enhanced sensitivity to variations in ambient light. Conversely, two different photoreceptors may be involved in the control of the same physiological response. Genomic analysis in marine diatoms, combined with phylogenetic studies, has also revealed the presence of blue and red light photoreceptors in the marine environment. This discovery has intriguing implications for the understanding of light perception and its evolution in photosynthetic organisms. In addition, the characterization of these photoreceptors likely will add to our understanding of photoreceptor diversity as an adaptation to different habitats.

Signaling mechanisms of higher plant photoreceptors: a structure-function perspective

Higher plants monitor changes in the ambient light environment using three major classes of photoreceptors: the red/far-red-absorbing phytochromes, the blue/UV-A-absorbing cryptochromes, and phototropins. These photoreceptors mediate various photoresponses, ranging from seed germination, to seedling de-etiolation, stem elongation, leaf expansion, floral initiation, phototropic bending of organs, intracellular movement of chloroplast, and stomata opening. Here I briefly review the distinct and overlapping physiological functions of these photoreceptors and highlight recent progress that provided significant insights into their signaling mechanisms, particularly from a structure-function perspective. This review focuses on the early photochemical and biochemical events that lead to photoreceptor activation and signaling initiation.

Promotion of photomorphogenesis by COP1

CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) represses photomorphogenesis in darkness by targeting nuclear-localized transcription factors to proteasome-mediated degradation. Upon light exposure, COP1 migrates to the cytosol allowing photomorphogenesis to proceed but the residual nuclear pool down-regulates light signaling mediated by phytochrome A. Here we show that weak alleles of cop1 exhibit reverse photomorphogenic responses i.e. reduced rather than enhanced cotyledon unfolding under red light compared to darkness. Conversely, COP1 overexpressors which de-etiolate poorly under blue or far-red light, showed enhanced photomorphogenesis under red light. The positive relationship between COP1 and photomorphogenic response required phytochrome B. Thus, genetic manipulation of COP1 levels differentially affects phytochrome A- compared to phytochrome B-mediated responses. We hypothesize that COP1 could be involved in degradation of negative regulators of photomorphogenesis or in transcriptional activation, as observed for some E3 ligases in mammalian development.

Light regulation of the Arabidopsis respiratory chain. Multiple discrete photoreceptor responses contribute to induction of type II NAD(P)H dehydrogenase genes

Controlled oxidation reactions catalyzed by the large, proton-pumping complexes of the respiratory chain generate an electrochemical gradient across the mitochondrial inner membrane that is harnessed for ATP production. However, several alternative respiratory pathways in plants allow the maintenance of substrate oxidation while minimizing the production of ATP. We have investigated the role of light in the regulation of these energy-dissipating pathways by transcriptional profiling of the alternative oxidase, uncoupling protein, and type II NAD(P)H dehydrogenase gene families in etiolated Arabidopsis seedlings. Expression of the nda1 and ndc1 NAD(P)H dehydrogenase genes was rapidly up-regulated by a broad range of light intensities and qualities. For both genes, light induction appears to be a direct transcriptional effect that is independent of carbon status. Mutant analyses demonstrated the involvement of two separate photoreceptor families in nda1 and ndc1 light regulation: the phytochromes (phyA and phyB) and an undetermined blue light photoreceptor. In the case of the nda1 gene, the different photoreceptor systems generate distinct kinetic induction profiles that are integrated in white light response. Primary transcriptional control of light response was localized to a 99-bp region of the nda1 promoter, which contains an I-box flanked by two GT-1 elements, an arrangement prevalent in the promoters of photosynthesis-associated genes. Light induction was specific to nda1 and ndc1. The only other substantial light effect observed was a decrease in aox2 expression. Overall, these results suggest that light directly influences the respiratory electron transport chain via photoreceptor-mediated transcriptional control, likely for supporting photosynthetic metabolism.

Phototropins mediate blue and red light-induced chloroplast movements in Physcomitrella patens

Phototropin is the blue-light receptor that mediates phototropism, chloroplast movement, and stomatal opening in Arabidopsis. Blue and red light induce chloroplast movement in the moss Physcomitrella patens. To study the photoreceptors for chloroplast movement in P. patens, four phototropin genes (PHOTA1, PHOTA2, PHOTB1, and PHOTB2) were isolated by screening cDNA libraries. These genes were classified into two groups (PHOTA and PHOTB) on the basis of their deduced amino acid sequences. Then phototropin disruptants were generated by homologous recombination and used for analysis of chloroplast movement. Data revealed that blue light-induced chloroplast movement was mediated by phototropins in P. patens. Both photA and photB groups were able to mediate chloroplast avoidance, as has been reported for Arabidopsis phot2, although the photA group contributed more to the response. Red light-induced chloroplast movement was also significantly reduced in photA2photB1photB2 triple disruptants. Because the primary photoreceptor for red light-induced chloroplast movement in P. patens is phytochrome, phototropins may be downstream components of phytochromes in the signaling pathway. To our knowledge, this work is the first to show a function for the phototropin blue-light receptor in a response to wavelengths that it does not absorb.