Small RNA-mediated silencing of phototropin suppresses the induction of photoprotection in the green alga Chlamydomonas reinhardtii.

Small RNAs (sRNAs) form complexes with Argonaute proteins and bind to transcripts with complementary sequences to repress gene expression. sRNA-mediated regulation is conserved in a diverse range of eukaryotes and is involved in the control of various physiological functions. sRNAs are present in the unicellular green alga Chlamydomonas reinhardtii, and genetic analyses revealed that the core sRNA biogenesis and action mechanisms are conserved with those of multicellular organisms. However, the roles of sRNAs in this organism remain largely unknown. Here, we report that Chlamydomonas sRNAs contribute to the induction of photoprotection. In this alga, photoprotection is mediated by LIGHT HARVESTING COMPLEX STRESS-RELATED 3 (LHCSR3), whose expression is induced by light signals through the blue-light receptor phototropin (PHOT). We demonstrate here that sRNA-defective mutants showed increased PHOT abundance leading to greater LHCSR3 expression. Disruption of the precursor for two sRNAs predicted to bind to the PHOT transcript also increased PHOT accumulation and LHCSR3 expression. The induction of LHCSR3 in the mutants was enhanced by light containing blue wavelengths, but not by red light, indicating that the sRNAs regulate the degree of photoprotection via regulation of PHOT expression. Our results suggest that sRNAs are involved not only in the regulation of photoprotection but also in biological phenomena regulated by PHOT signaling.

Light signaling in plants-a selective history.

In addition to providing the radiant energy that drives photosynthesis, sunlight carries signals that enable plants to grow, develop and adapt optimally to the prevailing environment. Here we trace the path of research that has led to our current understanding of the cellular and molecular mechanisms underlying the plant's capacity to perceive and transduce these signals into appropriate growth and developmental responses. Because a fully comprehensive review was not possible, we have restricted our coverage to the phytochrome and cryptochrome classes of photosensory receptors, while recognizing that the phototropin and UV classes also contribute importantly to the full scope of light-signal monitoring by the plant.

Out of the blue: Phototropins of the leaf vascular bundle sheath mediate the regulation of leaf hydraulic conductance by blue light.

The Arabidopsis (Arabidopsis thaliana) leaf veins bundle-sheath cells (BSCs)-a selective barrier to water and solutes entering the mesophyll-increase the leaf radial hydraulic conductance (Kleaf) by acidifying the xylem sap by their plasma membrane H+-ATPase,  AHA2. Based on this and on the BSCs' expression of phototropins PHOT1 and PHOT2, and the known blue light (BL)-induced Kleaf increase, we hypothesized that, resembling the guard cells, BL perception by the BSCs' phots activates its H+-ATPase, which, consequently, upregulates Kleaf. Indeed, under BL, the Kleaf of the knockout mutant lines phot1-5, phot2-1, phot1-5 phot2-1, and aha2-4 was lower than that of the wild-type (WT). BSC-only-directed complementation of phot1-5 or aha2-4 by PHOT1 or AHA2, respectively, restored the BL-induced Kleaf increase. BSC-specific silencing of PHOT1 or PHOT2 prevented such Kleaf increase. A xylem-fed kinase inhibitor (tyrphostin 9) replicated this also in WT plants. White light-ineffective in the phot1-5 mutant-acidified the xylem sap (relative to darkness) in WT and in the PHOT1-complemented phot1-5. These results, supported by BL increase of BSC protoplasts' water permeability and cytosolic pH and their hyperpolarization by BL, identify the BSCs as a second phot-controlled water conductance element in leaves, in series with stomatal conductance. Through both, BL regulates the leaf water balance.

Phototropin phosphorylation of ROOT PHOTOTROPISM 2 and its role in mediating phototropism, leaf positioning, and chloroplast accumulation movement in Arabidopsis.

Directional movements impact the ability of plants to respond and adjust their growth accordingly to the prevailing light environment. The plasma-membrane associated protein, ROOT PHOTOTROPISM 2 (RPT2) is a key signalling component involved in chloroplast accumulation movement, leaf positioning, and phototropism, all of which are regulated redundantly by the ultraviolet/blue light-activated AGC kinases phototropin 1 and 2 (phot1 and phot2). We recently demonstrated that members of the NON-PHOTOTROPIC HYPOCOTYL 3 (NPH3)/RPT2-like (NRL) family in Arabidopsis thaliana, including RPT2, are directly phosphorylated by phot1. However, whether RPT2 is a substrate for phot2, and the biological significance of phot phosphorylation of RPT2 remains to be determined. Here, we show that RPT2 is phosphorylated by both phot1 and phot2 at a conserved serine residue (S591) within the C-terminal region of the protein. Blue light triggered the association of 14-3-3 proteins with RPT2 consistent with S591 acting as a 14-3-3 binding site. Mutation of S591 had no effect on the plasma membrane localization of RPT2 but reduced its functionality for leaf positioning and phototropism. Moreover, our findings indicate that S591 phosphorylation within the C-terminus of RPT2 is required for chloroplast accumulation movement to low level blue light. Taken together, these findings further highlight the importance of the C-terminal region of NRL proteins and how its phosphorylation contributes to phot receptor signalling in plants.

Levels of photoactivated phototropin modulate signal transmission during the chloroplast accumulation response.

Chloroplasts accumulate in regions of plant cells exposed to irradiation to maximize light reception for efficient photosynthesis. This response is mediated by the blue-light receptor phototropin. Upon the perception of blue light, phototropin is photoactivated, an unknown signal is transmitted from the photoactivated phototropin to distant chloroplasts, and the chloroplasts begin their directional movement. How activated phototropin initiates this signal transmission is unknown. Here, using the liverwort Marchantia polymorpha, we analysed whether increased photoactive phototropin levels mediate signal transmission and chloroplast behaviour during the accumulation response. The signal transmission rate was higher in transgenic cells overexpressing phototropin than in wild-type cells. However, the chloroplast directional movement was similar between wild-type and transgenic cells. Consistent with the observation, increasing the amount of photoactivated phototropin through higher blue-light intensity also accelerated signal transmission but did not affect chloroplast behaviour in wild-type cells. Photoactivation of phototropin under weak blue-light led to the greater protein level of phosphorylated phototropin in cells overexpressing phototropin than in wild-type cells, whereas the autophosphorylation level within each phototropin molecule was similar. These results indicate that the abundance of photoactivated phototropin modulates the signal transmission rate to distant chloroplasts but does not affect chloroplast behaviour during the accumulation response.

A phytochrome/phototropin chimeric photoreceptor promotes growth of fern gametophytes under limited light conditions.

Many ferns thrive even in low-light niches such as under an angiosperm forest canopy. However, the shade adaptation strategy of ferns is not well understood. Phytochrome 3/neochrome (phy3/neo) is an unconventional photoreceptor, found in the fern Adiantum capillus-veneris, that controls both red and blue light-dependent phototropism and chloroplast photorelocation, which are considered to improve photosynthetic efficiency in ferns. Here we show that phy3/neo localizes not only at the plasma membrane but also in the nucleus. Since both phototropism and chloroplast photorelocation are mediated by membrane-associated phototropin photoreceptors, we speculated that nucleus-localized phy3/neo possesses a previously undescribed biological function. We reveal that phy3/neo directly interacts with Adiantum cryptochrome 3 (cry3) in the nucleus. Plant cryptochromes are blue light receptors that transcriptionally regulate photomorphogenesis; therefore, phy3/neo may function via cry3 to synchronize light-mediated development with phototropism and chloroplast photorelocation to promote fern growth under low-light conditions. Furthermore, we demonstrate that phy3/neo regulates the expression of the Cyclin-like gene AcCyc1 and promotes prothallium expansion growth. These findings provide insight into the shade adaptation strategy of ferns and suggest that phy3/neo plays a substantial role in the survival and growth of ferns during the tiny gametophytic stage under low-light conditions, such as those on the forest floor.

The new kid on the block: a dominant-negative mutation of phototropin1 enhances carotenoid content in tomato fruits.

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.

Phototropin-mediated perception of light direction in leaves regulates blade flattening.

One conserved feature among angiosperms is the development of flat thin leaves. This developmental pattern optimizes light capture and gas exchange. The blue light (BL) receptors phototropins are required for leaf flattening, with the null phot1phot2 mutant showing curled leaves in Arabidopsis (Arabidopsis thaliana). However, key aspects of their function in leaf development remain unknown. Here, we performed a detailed spatiotemporal characterization of phototropin function in Arabidopsis leaves. We found that phototropins perceive light direction in the blade, and, similar to their role in hypocotyls, they control the spatial pattern of auxin signaling, possibly modulating auxin transport, to ultimately regulate cell expansion. Phototropin signaling components in the leaf partially differ from hypocotyls. Moreover, the light response on the upper and lower sides of the leaf blade suggests a partially distinct requirement of phototropin signaling components on each side. In particular, NON PHOTOTROPIC HYPOCOTYL 3 showed an adaxial-specific function. In addition, we show a prominent role of PHYTOCHROME KINASE SUBSTRATE 3 in leaf flattening. Among auxin transporters, PIN-FORMED 3,4,7 and AUXIN RESISTANT 1 (AUX1)/LIKE AUXIN RESISTANT 1 (LAX1) are required for the response while ABCB19 has a regulatory role. Overall, our results show that directional BL perception by phototropins is a key aspect of leaf development, integrating endogenous and exogenous signals.

A blue-light photoreceptor mediates the feedback regulation of photosynthesis.

In plants and algae, light serves both as the energy source for photosynthesis and a biological signal that triggers cellular responses via specific sensory photoreceptors. Red light is perceived by bilin-containing phytochromes and blue light by the flavin-containing cryptochromes and/or phototropins (PHOTs), the latter containing two photosensory light, oxygen, or voltage (LOV) domains. Photoperception spans several orders of light intensity, ranging from far below the threshold for photosynthesis to values beyond the capacity of photosynthetic CO2 assimilation. Excess light may cause oxidative damage and cell death, processes prevented by enhanced thermal dissipation via high-energy quenching (qE), a key photoprotective response. Here we show the existence of a molecular link between photoreception, photosynthesis, and photoprotection in the green alga Chlamydomonas reinhardtii. We show that PHOT controls qE by inducing the expression of the qE effector protein LHCSR3 (light-harvesting complex stress-related protein 3) in high light intensities. This control requires blue-light perception by LOV domains on PHOT, LHCSR3 induction through PHOT kinase, and light dissipation in photosystem II via LHCSR3. Mutants deficient in the PHOT gene display severely reduced fitness under excessive light conditions, indicating that the sensing, utilization, and dissipation of light is a concerted process that plays a vital role in microalgal acclimation to environments of variable light intensities.

Engineering the phototropin photocycle improves photoreceptor performance and plant biomass production.

The ability to enhance photosynthetic capacity remains a recognized bottleneck to improving plant productivity. Phototropin blue light receptors (phot1 and phot2) optimize photosynthetic efficiency in Arabidopsis thaliana by coordinating multiple light-capturing processes. In this study, we explore the potential of using protein engineering to improve photoreceptor performance and thereby plant growth. We demonstrate that targeted mutagenesis can decrease or increase the photocycle lifetime of Arabidopsis phototropins in vitro and show that these variants can be used to reduce or extend the duration of photoreceptor activation in planta Our findings show that slowing the phototropin photocycle enhanced several light-capturing responses, while accelerating it reduced phototropin's sensitivity for chloroplast accumulation movement. Moreover, plants engineered to have a slow-photocycling variant of phot1 or phot2 displayed increased biomass production under low-light conditions as a consequence of their improved sensitivity. Together, these findings demonstrate the feasibility of engineering photoreceptors to manipulate plant growth and offer additional opportunities to enhance photosynthetic competence, particularly under suboptimal light regimes.

Phylogenomics-Based Reconstruction and Molecular Evolutionary Histories of Brassica Photoreceptor Gene Families.

Photosensory proteins known as photoreceptors (PHRs) are crucial for delineating light environments in synchronization with other environmental cues and regulating their physiological variables in plants. However, this has not been well studied in the Brassica genus, which includes several important agricultural and horticultural crops. Herein, we identified five major PHR gene families-phytochrome (PHY), cryptochrome (CRY), phototropin (PHOT), F-box containing flavin binding proteins (ZTL/FKF1/LKP2), and UV RESISTANCE LOCUS 8 (UVR8)-genomic scales and classified them into subfamilies based on their phylogenetic clustering with Arabidopsis homologues. The molecular evolution characteristics of Brassica PHR members indicated indirect expansion and lost one to six gene copies at subfamily levels. The segmental duplication was possibly the driving force of the evolution and amplification of Brassica PHRs. Gene replication retention and gene loss events of CRY, PHY, and PHOT members found in diploid progenitors were highly conserved in their tetraploid hybrids. However, hybridization events were attributed to quantitative changes in UVR8 and ZTL/FKF1/LKP2 members. All PHR members underwent purifying selection. In addition, the transcript expression profiles of PHR genes in different tissue and in response to exogenous ABA, and abiotic stress conditions suggested their multiple biological significance. This study is helpful in understanding the molecular evolution characteristics of Brassica PHRs and lays the foundation for their functional characterization.

FERONIA is involved in phototropin 1-mediated blue light phototropic growth in Arabidopsis.

Plant shoot phototropism is triggered by the formation of a light-driven auxin gradient leading to bending growth. The blue light receptor phototropin 1 (phot1) senses light direction, but how this leads to auxin gradient formation and growth regulation remains poorly understood. Previous studies have suggested phot1's role for regulated apoplastic acidification, but its relation to phototropin and hypocotyl phototropism is unclear. Herein, we show that blue light can cause phot1 to interact with and phosphorylate FERONIA (FER), a known cell growth regulator, and trigger downstream phototropic bending growth in Arabidopsis hypocotyls. fer mutants showed defects in phototropic growth, similar to phot1/2 mutant. FER also interacts with and phosphorylates phytochrome kinase substrates, the phot1 downstream substrates. The phot1-FER pathway acts upstream of apoplastic acidification and the auxin gradient formation in hypocotyl under lateral blue light, both of which are critical for phototropic bending growth in hypocotyls. Our study highlights a pivotal role of FER in the phot1-mediated phototropic cell growth regulation in plants.

Chloroplast relocation movement in the liverwort Apopellia endiviifolia.

Changes in the subcellular localisation of chloroplasts help optimise photosynthetic activity under different environmental conditions. In many plants, this movement is mediated by the blue-light photoreceptor phototropin. A model organism with simple phototropin signalling that allows clear observation of chloroplasts would facilitate the study of chloroplast relocation movement. Here, we examined this process in the simple thalloid liverwort Apopellia endiviifolia. Transverse sections of the thallus tissue showed uniformly developed chloroplasts and no air chambers; these characteristics enable clear observation of chloroplasts and analysis of their movements under a fluorescence stereomicroscope. At 22°C, the chloroplasts moved to the anticlinal walls of cells next to the neighbouring cells in the dark (dark-positioning response), whereas they moved towards weak light (accumulation response) and away from strong light (avoidance response). When the temperature was reduced to 5°C, the chloroplasts moved away from weak light (cold-avoidance response). Hence, both light- and temperature-dependent chloroplast relocation movements occur in A. endiviifolia. Notably, the accumulation, avoidance and cold-avoidance responses were induced under blue-light but not under red-light. These results suggest that phototropin is responsible for chloroplast relocation movement in A. endiviifolia and that the characteristics are similar to those in the model liverwort Marchantia polymorpha. RNA sequencing and Southern blot analysis identified a single copy of the PHOTOTROPIN gene in A. endiviifolia, indicating that a simple phototropin signalling pathway functions in A. endiviifolia. We conclude that A. endiviifolia has great potential as a model system for elucidating the mechanisms of chloroplast relocation movement.

Impairment of chloroplast movement reduces growth and delays reproduction of Arabidopsis thaliana in natural and controlled conditions.

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.

Chloroplasts in C3 grasses move in response to blue-light.

KEY MESSAGE: Brachypodium distachyon is a good model for studying chloropla st movements in the crop plants, wheat, rye and barley. The movements are activated only by blue light, similar to Arabidopsis. Chloroplast translocations are ubiquitous in photosynthetic organisms. On the one hand, they serve to optimize energy capture under limiting light, on the other hand, they minimize potential photodamage to the photosynthetic apparatus in excess light. In higher plants chloroplast movements are mediated by phototropins (phots), blue light receptors that also control other light acclimation responses. So far, Arabidopsis thaliana has been the main model for studying the mechanism of blue light signaling to chloroplast translocations in terrestrial plants. Here, we propose Brachypodium distachyon as a model in research into chloroplast movements in C3 cereals. Brachypodium chloroplasts respond to light in a similar way to those in Arabidopsis. The amino acid sequence of Brachypodium PHOT1 is 79.3% identical, and that of PHOT2 is 73.6% identical to the sequence of the corresponding phototropin in Arabidopsis. Both phototropin1 and 2 are expressed in Brachypodium, as shown using quantitative real-time PCR. Intriguingly, the light-expression pattern of BradiPHOT1 and BradiPHOT2 is the opposite of that for Arabidopsis phototropins, suggesting potential unique light signaling in C3 grasses. To investigate if Brachypodium is a good model for studying grass chloroplast movements we analyzed these movements in the leaves of three C3 crop grasses, namely wheat, rye and barley. Similarly to Brachypodium, chloroplasts only respond to blue light in all these species.

Phototropin perceives temperature based on the lifetime of its photoactivated state.

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.

An optogenetic approach to control protein localization during embryogenesis of the sea urchin.

Light inducible protein-protein interactions have been used to manipulate protein localization and function in the cell with utmost spatial and temporal precision. In this technical report, we use a recently developed optogenetic approach to manipulate protein localization in the developing sea urchin embryo. A photosensitive LOV domain from Avena sativa phototropin1 cages a small peptide that binds the engineered PDZ domain (ePDZ) upon blue light irradiation. Using this system, mCherry tagged proteins fused with the LOV domain were recruited to ectopic sub-cellular regions such as the membrane, microtubules, or actin by GFP tagged proteins fused with the ePDZ domain upon blue light irradiation within 1-3 min in the sea urchin embryo. The efficiency and speed of recruitment of each protein to its respective subcellular region appeared to be dependent on the power and duration of laser irradiation, as well as the respective level of affinity to the tagged location. Controlled laser irradiation allowed partial recruitment of the spindle to the membrane, and resulted in cell blebbing. Vasa, a cell cycle and germline factor that localizes on the spindle and enriches in the micromeres at 8-16 cell stage was recruited to ectopic sites, preventing normal enrichment. Continuous blue light activation with a regular blue aquarium light over two days of culture successfully induced LOV-ePDZ binding in the developing embryos, resulting in continued ectopic recruitment of Vasa and failure in gastrulation at Day 2. Although some cytotoxicity was observed with prolonged blue light irradiation, this optogenetic system provides a promising approach to test the sub-cellular activities of developmental factors, as well as to alter protein localization and development during embryogenesis.

Phototropins Mediate Chloroplast Movement in Phalaenopsis aphrodite (Moth Orchid).

Chloroplast movement is important for plants to avoid photodamage and to perform efficient photosynthesis. Phototropins are blue light receptors in plants that function in chloroplast movement, phototropism, stomatal opening, and they also affect plant growth and development. In this study, full-length cDNAs of two PHOTOTROPIN genes, PaPHOT1 and PaPHOT2, were cloned from a moth orchid Phalaenopsis aphrodite, and their functions in chloroplast movement were investigated. Phylogenetic analysis showed that PaPHOT1 and PaPHOT2 orthologs were highly similar to PHOT1 and PHOT2 of the close relative Phalaenopsis equestris, respectively, and clustered with monocots PHOT1 and PHOT2 orthologs, respectively. Phalaenopsis aphrodite expressed a moderate level of PaPHOT1 under low blue light of 5 µmol�m-2�s-1 (BL5) and a high levels of PaPHOT1 at >BL100. However, PaPHOT2 was expressed at low levels at BL100. Analysis of light-induced chloroplast movements using the SPAD method indicated that orchid accumulated chloroplasts at BL25 and significant chloroplast avoidance movement was observed at >BL100. Virus-induced gene silencing of PaPHOTs in orchids showed decreased gene expression of PaPHOTs and reduced both chloroplast accumulation and avoidance responses. Heterologous expression of PaPHOT1 in Arabidopsis phot1phot2 double mutant recovered chloroplast accumulation response at BL5, but neither PaPHOT1 nor PaPHOT2 was able to restore mutant chloroplast avoidance at BL100. Overall, this study showed that phototropins mediate chloroplast movement in Phalaenopsis orchid is blue light-dependent but their function is slightly different from Arabidopsis which might be due to gene evolution.

Chloroplast Accumulation Response Enhances Leaf Photosynthesis and Plant Biomass Production.

Under high light intensity, chloroplasts avoid absorbing excess light by moving to anticlinal cell walls (avoidance response), but under low light intensity, chloroplasts accumulate along periclinal cell walls (accumulation response). In most plant species, these responses are induced by blue light and are mediated by the blue light photoreceptor, phototropin, which also regulates phototropism, leaf flattening, and stomatal opening. These phototropin-mediated responses could enhance photosynthesis and biomass production. Here, using various Arabidopsis (Arabidopsis thaliana) mutants deficient in chloroplast movement, we demonstrated that the accumulation response enhances leaf photosynthesis and plant biomass production. Conspicuously, phototropin2 mutant plants specifically defective in the avoidance response but not in other phototropin-mediated responses displayed a constitutive accumulation response irrespective of light intensities, enhanced leaf photosynthesis, and increased plant biomass production. Therefore, our findings provide clear experimental evidence of the importance of the chloroplast accumulation response in leaf photosynthesis and biomass production.

Induction of Signal Transduction by Using Non-Channelrhodopsin-Type Optogenetic Tools.

Signal transductions are the basis for all cellular functions. Previous studies investigating signal transductions mainly relied on pharmacological inhibition, RNA interference, and constitutive active/dominant negative protein expression systems. However, such studies do not allow the modulation of protein activity with high spatial and temporal precision in cells, tissues, and organs in animals. Recently, non-channelrhodopsin-type optogenetic tools for regulating signal transduction have emerged. These photoswitches address several disadvantages of previous techniques, and allow us to control a variety of signal transductions such as cell membrane dynamics, calcium signaling, lipid signaling, and apoptosis. In this review we summarize recent advances in the development of such photoswitches and in how these optotools are applied to signaling processes.