Photoactivation and inactivation of Arabidopsis cryptochrome 2

Arabidopsis cryptochromes interact with SOG1 to promote the repair of DNA double-strand breaks

Cryptochromes (CRYs) are blue light (BL) photoreceptors to regulate a variety of physiological processes including DNA double-strand break (DSB) repair. SUPPRESSOR OF GAMMA RADIATION 1 (SOG1) acts as the central transcription factor of DNA damage response (DDR) to induce the transcription of downstream genes, including DSB repair-related genes BRCA1 and RAD51. Whether CRYs regulate DSB repair by directly modulating SOG1 is unknown. Here, we demonstrate that CRYs physically interact with SOG1. Disruption of CRYs and SOG1 leads to increased sensitivity to DSBs and reduced DSB repair-related genes' expression under BL. Moreover, we found that CRY1 enhances SOG1's transcription activation of DSB repair-related gene BRCA1. These results suggest that the mechanism by which CRYs promote DSB repair involves positive regulation of SOG1's transcription of its target genes, which is likely mediated by CRYs-SOG1 interaction.

Rice CRYPTOCHROME-INTERACTING BASIC HELIX-LOOP-HELIX 1-LIKE interacts with OsCRY2 and promotes flowering by upregulating Early heading date 1

Flowering time is a crucial adaptive response to seasonal variation in plants and is regulated by environmental cues such as photoperiod and temperature. In this study, we demonstrated the regulatory function of rice CRYPTOCHROME-INTERACTING BASIC HELIX-LOOP-HELIX 1-LIKE (OsCIBL1) in flowering time. Overexpression of OsCIB1L promoted flowering, whereas the oscib1l knockout mutation did not alter flowering time independent of photoperiodic conditions. Cryptochromes (CRYs) are blue light photoreceptors that enable plants to sense photoperiodic changes. OsCIBL1 interacted with OsCRY2, a member of the rice CRY family (OsCRY1a, OsCRY1b, and OsCRY2), and bound to the Early heading date 1 (Ehd1) promoter, activating the rice-specific Ehd1-Heading date 3a/RICE FLOWERING LOCUS T 1 pathway for flowering induction. Dual-luciferase reporter assays showed that the OsCIBL1-OsCRY2 complex required blue light to induce Ehd1 transcription. Natural alleles resulting from nonsynonymous single nucleotide polymorphisms in OsCIB1L and OsCRY2 may contribute to the adaptive expansion of rice cultivation areas. These results expand our understanding of the molecular mechanisms controlling rice flowering and highlight the importance of blue light-responsive genes in the geographic distribution of rice.

ADA2b acts to positively regulate blue light-mediated photomorphogenesis in Arabidopsis

Cryptochromes (CRYs) act as blue light photoreceptors to regulate various plant physiological processes including photomorphogenesis and repair of DNA double strand breaks (DSBs). ADA2b is a conserved transcription co-activator that is involved in multiple plant developmental processes. It is known that ADA2b interacts with CRYs to mediate blue light-promoted DSBs repair. Whether ADA2b may participate in CRYs-mediated photomorphogenesis is unknown. Here we show that ADA2b acts to inhibit hypocotyl elongation and hypocotyl cell elongation in blue light. We found that the SWIRM domain-containing C-terminus mediates the blue light-dependent interaction of ADA2b with CRYs in blue light. Moreover, ADA2b and CRYs act to co-regulate the expression of hypocotyl elongation-related genes in blue light. Based on previous studies and these results, we propose that ADA2b plays dual functions in blue light-mediated DNA damage repair and photomorphogenesis.

Blue light photoreceptor cryptochrome 1 promotes wood formation and anthocyanin biosynthesis in Populus

Blue light photoreceptor cryptochrome 1 (CRY1) in herbaceous plants plays crucial roles in various developmental processes, including cotyledon expansion, hypocotyl elongation and anthocyanin biosynthesis. However, the function of CRY1 in perennial trees is unclear. In this study, we identified two ortholog genes of CRY1 (PagCRY1a and PagCRY1b) from Populus, which displayed high sequence similarity to Arabidopsis CRY1. Overexpression of PagCRY1 substantially inhibited plant growth and promoted secondary xylem development in Populus, while CRISPR/Cas9-mediated knockout of PagCRY1 enhanced plant growth and delayed secondary xylem development. Moreover, overexpression of PagCRY1 dramatically increased anthocyanin accumulation. The further analysis supported that PagCRY1 functions specifically in response to blue light. Taken together, our results demonstrated that modulating the expression of blue light photoreceptor CRY1 ortholog gene in Populus could significantly influence plant biomass production and the process of wood formation, laying a foundation for further investigating the light-regulated tree growth.

Leaf and shoot apical meristem transcriptomes of quinoa (Chenopodium quinoa Willd.) in response to photoperiod and plant development

Understanding the regulation of flowering time is crucial for adaptation of crops to new environment. In this study, we examined the timing of floral transition and analysed transcriptomes in leaf and shoot apical meristems of photoperiod-sensitive and -insensitive quinoa accessions. Histological analysis showed that floral transition in quinoa initiates 2-3 weeks after sowing. We found four groups of differentially expressed genes in quinoa genome that responded to plant development and floral transition: (i) 222 genes responsive to photoperiod in leaves, (ii) 1812 genes differentially expressed between accessions under long-day conditions in leaves, (iii) 57 genes responding to developmental changes under short-day conditions in leaves and (iv) 911 genes responding to floral transition within the shoot apical meristem. Interestingly, among numerous candidate genes, two putative FT orthologs together with other genes (e.g. SOC1, COL, AP1) were previously reported as key regulators of flowering time in other species. Additionally, we used coexpression networks to associate novel transcripts to a putative biological process based on the annotated genes within the same coexpression cluster. The candidate genes in this study would benefit quinoa breeding by identifying and integrating their beneficial haplotypes in crossing programs to develop adapted cultivars to diverse environmental conditions.

CaWRKY01-10 and CaWRKY08-4 Confer Pepper's Resistance to Phytophthora capsici Infection by Directly Activating a Cluster of Defense-Related Genes

Phytophthora blight of pepper, which is caused by the notorious oomycete pathogen Phytophthora capsici, is a serious disease in global pepper production regions. Our previous study had identified two WRKY transcription factors (TFs), CaWRKY01-10 and CaWRKY08-4, which are prominent modulators in the resistant pepper line CM334 against P. capsici infection. However, their functional mechanisms and underlying signaling networks remain unknown. Herein, we determined that CaWRKY01-10 and CaWRKY08-4 are localized in plant nuclei. Transient overexpression assays indicated that both CaWRKY01-10 and CaWRKY08-4 act as positive regulators in pepper resistance to P. capsici. Besides, the stable overexpression of CaWRKY01-10 and CaWRKY08-4 in transgenic Nicotiana benthamiana plants also significantly enhanced the resistance to P. capsici. Using comprehensive approaches including RNA-seq, CUT&RUN-qPCR, and dual-luciferase reporter assays, we revealed that overexpression of CaWRKY01-10 and CaWRKY08-4 can activate the expressions of the same four Capsicum annuum defense-related genes (one PR1, two PR4, and one pathogen-related gene) by directly binding to their promoters. However, we did not observe protein-protein interactions and transcriptional amplification/inhibition effects of their shared target genes when coexpressing these two WRKY TFs. In conclusion, these data suggest that both of the resistant line specific upregulated WRKY TFs (CaWRKY01-10 and CaWRKY08-4) can confer pepper's resistance to P. capsici infection by directly activating a cluster of defense-related genes and are potentially useful for genetic improvement against Phytophthora blight of pepper and other crops.

The dual-action mechanism of Arabidopsis cryptochromes

Photoreceptor cryptochromes (CRYs) mediate blue-light regulation of plant growth and development. It has been reported that Arabidopsis CRY1and CRY2 function by physically interacting with at least 84 proteins, including transcription factors or co-factors, chromatin regulators, splicing factors, messenger RNA methyltransferases, DNA repair proteins, E3 ubiquitin ligases, protein kinases and so on. Of these 84 proteins, 47 have been reported to exhibit altered binding affinity to CRYs in response to blue light, and 41 have been shown to exhibit condensation to CRY photobodies. The blue light-regulated composition or condensation of CRY complexes results in changes of gene expression and developmental programs. In this mini-review, we analyzed recent studies of the photoregulatory mechanisms of Arabidopsis CRY complexes and proposed the dual mechanisms of action, including the "Lock-and-Key" and the "Liquid-Liquid Phase Separation (LLPS)" mechanisms. The dual CRY action mechanisms explain, at least partially, the structural diversity of CRY-interacting proteins and the functional diversity of the CRY photoreceptors.

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.

Genome-wide identification and expression analysis of the cryptochromes reveal the CsCRY1 role under low-light-stress in cucumber

Introduction

Low-light-stress is a common meteorological disaster that can result in slender seedlings. The photoreceptors play a crucial role in perceiving and regulating plants' tolerance to low-light-stress. However, the low-light-stress tolerance of cucumber has not been effectively evaluated, and the functions of these photoreceptor genes in cucumber, particularly under low-light-stress conditions, are not clear.

Methods

Herein, we evaluated the growth characteristics of cucumber seedlings under various LED light treatment. The low-light-stress tolerant cucumber CR and intolerant cucumber CR were used as plant materials for gene expression analysis, and then the function of CsCRY1 was analyzed.

Results

The results revealed that light treatment below 40 μmol m-2 s-1 can quickly and effectively induce low-light-stress response. Then, cucumber CR exhibited remarkable tolerance to low-light-stress was screened. Moreover, a total of 11 photoreceptor genes were identified and evaluated. Among them, the cryptochrome 1 (CRY1) had the highest expression level and was only induced in the low-light sensitive cucumber CS. The transcript CsaV3_3G047490.1 is predicted to encode a previously unknown CsCRY1 protein, which lacks 70 amino acids at its C-terminus due to alternative 5' splice sites within the final intron of the CsCRY1 gene.

Discussion

CRY1 is a crucial photoreceptor that plays pivotal roles in regulating plants' tolerance to low-light stress. In this study, we discovered that alternative splicing of CsCRY1 generates multiple transcripts encoding distinct CsCRY1 protein variants, providing valuable insights for future exploration and utilization of CsCRY1 in cucumber.

Optical Control over Liquid–Liquid Phase Separation

Liquid-liquid phase separation (LLPS) is responsible for the emergence of intracellular membrane-less organelles and the development of coacervate protocells. Benefitting from the advantages of simplicity, precision, programmability, and noninvasiveness, light has become an effective tool to regulate the assembly dynamics of LLPS, and mediate various biochemical processes associated with LLPS. In this review, recent advances in optically controlling membrane-less organelles within living organisms are summarized, thereby modulating a series of biological processes including irreversible protein aggregation pathologies, transcription activation, metabolic flux, genomic rearrangements, and enzymatic reactions. Among these, the intracellular systems (i.e., optoDroplet, Corelet, PixELL, CasDrop, and other optogenetic systems) that enable the photo-mediated control over biomolecular condensation are highlighted. The design of photoactive complex coacervate protocells in laboratory settings by utilizing photochromic molecules such as azobenzene and diarylethene is further discussed. This review is expected to provide in-depth insights into phase separation-associated biochemical processes, bio-metabolism, and diseases.

Dual-transgenic BiFC vector systems for protein-protein interaction analysis in plants

Protein-protein interaction (PPI) play a pivotal role in cellular signal transduction. The bimolecular fluorescence complementation (BiFC) assay offers a rapid and intuitive means to ascertain the localization and interactions of target proteins within living cells. BiFC is based on fluorescence complementation by reconstitution of a functional fluorescent protein by co-expression of N- and C-terminal fragments of this protein. When fusion proteins interact, the N- and C-terminal fragments come into close proximity, leading to the reconstitution of the fluorescent protein. In the conventional approach, the N-terminal and C-terminal fragments of the fluorescent protein are typically expressed using two separate vectors, which largely relies on the efficiency of the transformation of the two vectors in the same cells. Furthermore, issues of vector incompatibility can often result in loss of one plasmid. To address these challenges, we have developed novel dual-transgenic BiFC vectors, designed as pDTQs, derived from the previously published pDT1 vector. This set of BiFC vectors offers the following advantages: 1) Both fluorescent fusion proteins are expressed sequentially within a single vector, enhancing expression efficiency; 2) Independent promoters and terminators regulate the expression of the two proteins potentially mitigating vector compatibility issues; 3) A long linker is inserted between the fluorescent protein fragment and the gene of interest, facilitating the recombination of the fused fluorescent protein into an active form; 4) Four distinct types of fluorescent proteins, namely, EYFP, mVenus, mRFP1Q66T and mCherry are available for BiFC analysis. We assessed the efficiency of the pDTQs system by investigating the oligomerization of Arabidopsis CRY2 and CRY2-BIC2 interactions in N. benthamiana. Notably, the pDTQs were found to be applicable in rice, underscoring their potential utility across various plant species.

Decoding plant adaptation: deubiquitinating enzymes UBP12 and UBP13 in hormone signaling, light response, and developmental processes

Ubiquitination, a vital post-translational modification in plants, plays a significant role in regulating protein activity, localization, and stability. This process occurs through a complex enzyme cascade that involves E1, E2, and E3 enzymes, leading to the covalent attachment of ubiquitin molecules to substrate proteins. Conversely, deubiquitinating enzymes (DUBs) work in opposition to this process by removing ubiquitin moieties. Despite extensive research on ubiquitination in plants, our understanding of the function of DUBs is still emerging. UBP12 and UBP13, two plant DUBs, have received much attention recently and are shown to play pivotal roles in hormone signaling, light perception, photoperiod responses, leaf development, senescence, and epigenetic transcriptional regulation. This review summarizes current knowledge of these two enzymes, highlighting the central role of deubiquitination in regulating the abundance and activity of critical regulators such as receptor kinases and transcription factors during phytohormone and developmental signaling.

Deciphering transcriptomic signatures explaining the phenotypic plasticity of nonheading lettuce genotypes under artificial light conditions

Elucidating the mechanisms and pathways involved in genotype-environment (G×E) interactions and phenotypic plasticity is critical for improving plant growth. Controlled environment agricultural systems allow growers to modulate the environment for particular genotypes. In this study, we evaluated the effects of interactions among 14 genotypes and four artificial light environments on leaf lettuce phenotypes and dissected the underlying molecular mechanism via transcriptome-based modeling. Variations in morphological traits and phytochemical concentrations in response to artificial light treatments revealed significant G×E interactions. The appropriate genotype and artificial light combinations for maximizing phenotypic expression were determined on the basis of a joint regression analysis and the additive main effect and multiplicative interaction model for these G×E interactions. Transcriptome-based regression modeling explained approximately 50%-90% of the G×E variations. Further analyzes indicated Red Lettuce Leaves 4 (RLL4) regulates UV-B and blue light signaling through the effects of the HY5-MBW pathway on flavonoid biosynthesis and contributes to natural variations in the light-responsive plasticity of lettuce traits. Our study represents an important step toward elucidating the phenotypic variations due to G×E interactions in nonheading lettuce under artificial light conditions.

Light-induced LLPS of the CRY2/SPA1/FIO1 complex regulating mRNA methylation and chlorophyll homeostasis in Arabidopsis

Light regulates chlorophyll homeostasis and photosynthesis via various molecular mechanisms in plants. The light regulation of transcription and protein stability of nuclear-encoded chloroplast proteins have been extensively studied, but how light regulation of mRNA metabolism affects abundance of nuclear-encoded chloroplast proteins and chlorophyll homeostasis remains poorly understood. Here we show that the blue light receptor cryptochrome 2 (CRY2) and the METTL16-type m6A writer FIONA1 (FIO1) regulate chlorophyll homeostasis in response to blue light. In contrast to the CRY2-mediated photo-condensation of the mRNA adenosine methylase (MTA), photoexcited CRY2 co-condenses FIO1 only in the presence of the CRY2-signalling protein SUPPRESSOR of PHYTOCHROME A (SPA1). CRY2 and SPA1 synergistically or additively activate the RNA methyltransferase activity of FIO1 in vitro, whereas CRY2 and FIO1, but not MTA, are required for the light-induced methylation and translation of the mRNAs encoding multiple chlorophyll homeostasis regulators in vivo. Our study demonstrates that the light-induced liquid-liquid phase separation of the photoreceptor/writer complexes is commonly involved in the regulation of photoresponsive changes of mRNA methylation, whereas the different photo-condensation mechanisms of the CRY/FIO1 and CRY/MTA complexes explain, at least partially, the writer-specific functions in plant photomorphogenesis.

Role of Phytochromes in Red Light-Regulated Alternative Splicing in Arabidopsis thaliana: Impactful but Not Indispensable

Light is both the main source of energy and a key environmental signal for plants. It regulates not only gene expression but also the tightly related processes of splicing and alternative splicing (AS). Two main pathways have been proposed to link light sensing with the splicing machinery. One occurs through a photosynthesis-related signal, and the other is mediated by photosensory proteins, such as red light-sensing phytochromes. Here, we evaluated the relative contribution of each of these pathways by performing a transcriptome-wide analysis of light regulation of AS in plants that do not express any functional phytochrome (phyQ). We found that an acute 2-h red-light pulse in the middle of the night induces changes in the splicing patterns of 483 genes in wild-type plants. Approximately 30% of these genes also showed strong light regulation of splicing patterns in phyQ mutant plants, revealing that phytochromes are important but not essential for the regulation of AS by R light. We then performed a meta-analysis of related transcriptomic datasets and found that different light regulatory pathways can have overlapping targets in terms of AS regulation. All the evidence suggests that AS is regulated simultaneously by various light signaling pathways, and the relative contribution of each pathway is highly dependent on the plant developmental stage.

Identification of two Bacillus thuringiensis Cry3Aa toxin-binding aminopeptidase N from Rhynchophorus ferrugineus (Coleoptera: Curculionidae)

Rhynchophorus ferrugineus is a quarantine pest that mainly damages plants in tropical regions, which are essential economic resources. Cry3Aa has been used to control coleopteran pests and is known to be toxic to R. ferrugineus. The binding of the Cry toxin to specific receptors on the target insect plays a crucial role in the toxicological mechanism of Cry toxins. However, in the case of R. ferrugineus, the nature and identity of the receptor proteins involved remain unknown. In the present study, pull-down assays and mass spectrometry were used to identify two proteins of aminopeptidase N proteins (RfAPN2a and RfAPN2b) in the larval midguts of R. ferrugineus. Cry3Aa was able to bind to RfAPN2a (Kd = 108.5 nM) and RfAPN2b (Kd = 68.2 nM), as well as midgut brush border membrane vesicles (Kd = 482.5 nM). In silico analysis of both RfAPN proteins included the signal peptide and anchored sites for glycosyl phosphatidyl inositol. In addition, RfAPN2a and RfAPN2b were expressed in the human embryonic kidney 293T cell line, and cytotoxicity assays showed that the transgenic cells were not susceptible to activated Cry3Aa. Our results show that RfAPN2a and RfAPN2b are Cry3Aa-binding proteins involved in the Cry3Aa toxicity of R. ferrugineus. This study deepens our understanding of the action mechanism of Cry3Aa in R. ferrugineus larvae.

Comparison of Policosanol Profiles of the Sprouts of Wheat Mutant Lines and the Effect of Differential LED Lights on Selected Lines

Policosanols (PCs) are long-chain linear aliphatic alcohols that are present in the primary leaves of cereal crops, such as barley and wheat, sugar cane wax, and beeswax. PCs have been used as a nutraceutical for improving hyperlipidemia and hypercholesterolemia. However, the PC content in mutant wheat lines has not been investigated. To select highly functional wheat sprouts with a high content of PCs in wheat mutant lines developed via gamma-irradiated mutation breeding, we cultivated the sprouts of wheat mutant lines in a growth chamber with white LED light (6000 K) and analyzed the PC content in these samples using GC-MS. We studied the PC content in 91 wheat sprout samples: the original variety (Woori-mil × D-7; WS01), commercially available cv. Geumgang (WS87) and cv. Cheongwoo (WS91), and mutant lines (WS02-WS86 and WS88-WS90) developed from WS01 and WS87. Compared to WS01, 18 mutant lines exhibited a high total PC content (506.08-873.24 mg/100 g dry weight). Among them, the top 10 mutant lines were evaluated for their PC production after cultivating under blue (440 nm), green (520 nm), and red (660 nm) LED light irradiation; however, these colored LED lights reduced the total PC production by 35.8-49.7%, suggesting that the cultivation with white LED lights was more efficient in promoting PCs' yield, compared to different LED lights. Therefore, our findings show the potential of radiation-bred wheat varieties as functional foods against hyperlipidemia and obesity and the optimal light conditions for high PC production.

Cryptochromes in mammals: a magnetoreception misconception?

Cryptochromes are flavoproteins related to photolyases that are widespread throughout the plant and animal kingdom. They govern blue light-dependent growth in plants, control circadian rhythms in a light-dependent manner in invertebrates, and play a central part in the circadian clock in vertebrates. In addition, cryptochromes might function as receptors that allow animals to sense the Earth's magnetic field. As cryptochromes are also present in mammals including humans, the possibility of a magnetosensitive protein is exciting. Here we attempt to provide a concise overview of cryptochromes in mammals. We briefly review their canonical role in the circadian rhythm from the molecular level to physiology, behaviour and diseases. We then discuss their disputed light sensitivity and proposed role in the magnetic sense in mammals, providing three mechanistic hypotheses. Specifically, mammalian cryptochromes could form light-induced radical pairs in particular cellular milieus, act as magnetoreceptors in darkness, or as secondary players in a magnetoreception signalling cascade. Future research can test these hypotheses to investigate if the role of mammalian cryptochromes extends beyond the circadian clock.

Co-condensation with photoexcited cryptochromes facilitates MAC3A to positively control hypocotyl growth in Arabidopsis

Cryptochromes (CRYs) are blue light receptors that mediate plant photoresponses through regulating gene expressions. We recently reported that Arabidopsis CRY2 could form light-elicited liquid condensates to control RNA methylation. However, whether CRY2 condensation is involved in other gene expression-regulatory processes remains unclear. Here, we show that MOS4-associated complex subunits 3A and 3B (MAC3A/3B) are CRY-interacting proteins and assembled into nuclear CRY condensates. mac3a3b double mutants exhibit hypersensitive photoinhibition of hypocotyl elongation, suggesting that MAC3A/3B positively control hypocotyl growth. We demonstrate the noncanonical activity of MAC3A as a DNA binding protein that modulates transcription. Genome-wide mapping of MAC3A-binding sites reveals that blue light enhances the association of MAC3A with its DNA targets, which requires CRYs. Further evidence indicates that MAC3A and ELONGATED HYPOCOTYL 5 (HY5) occupy overlapping genomic regions and compete for the same targets. These results argue that photocondensation of CRYs fine-tunes light-responsive hypocotyl growth by balancing the opposed effects of HY5 and MAC3A.

Arabidopsis NF-YC7 Interacts with CRY2 and PIF4/5 to Repress Blue Light-Inhibited Hypocotyl Elongation

Light is an important environmental factor. Plants adapt to their light environment by developing the optimal phenotypes. Light-mediated hypocotyl growth is an ideal phenotype for studying how plants respond to light. Thus far, many signaling components in light-mediated hypocotyl growth have been reported. Here, we focused on identifying the transcription factors (TFs) involved in blue light-mediated hypocotyl growth. We analyzed the blue-light-mediated hypocotyl lengths of Arabidopsis TF-overexpressing lines and identified three NF-YC proteins, NF-YC7, NF-YC5, and NF-YC8 (NF-YCs being the short name), as the negative regulators in blue light-inhibited hypocotyl elongation. NF-YC-overexpressing lines developed longer hypocotyls than those of the wild type under blue light, while the deficient mutants nf-yc5nf-yc7 and nf-yc7nf-yc8 failed to exhibit hypocotyl elongation under blue light. NF-YCs physically interacted with CRY2 (cryptochrome 2) and PIF4/5 (phytochrome interacting factor 4 or 5), while the NF-YCs-PIF4/5 interactions were repressed by CRY2. Moreover, the overexpression of CRY2 or deficiency of PIF4/5 repressed NF-YC7-induced hypocotyl elongation under blue light. Further investigation revealed that NF-YC7 may increase CRY2 degradation and regulate PIF4/5 activities under blue light. Taken together, this study will provide new insight into the mechanism of how blue light inhibits hypocotyl elongation.

BIC2, a Cryptochrome Function Inhibitor, Is Involved in the Regulation of ABA Responses in Arabidopsis

The plant hormone ABA (abscisic acid) is able to regulate plant responses to abiotic stresses via regulating the expression of ABA response genes. BIC1 (Blue-light Inhibitor of Cryptochromes 1) and BIC2 have been identified as the inhibitors of plant cryptochrome functions, and are involved in the regulation of plant development and metabolism in Arabidopsis . In this study, we report the identification of BIC2 as a regulator of ABA responses in Arabidopsis . RT-PCR (Reverse Transcription-Polymerase Chain Reaction) results show that the expression level of BIC1 remained largely unchanged, but that of BIC2 increased significantly in response to ABA treatment. Transfection assays in Arabidopsis protoplasts show that both BIC1 and BIC2 were mainly localized in the nucleus, and were able to activate the expression of the co-transfected reporter gene. Results in seed germination and seedling greening assays show that ABA sensitivity was increased in the transgenic plants overexpressing BIC2, but increased slightly, if any, in the transgenic plants overexpressing BIC1. ABA sensitivity was also increased in the bic2 single mutants in seedling greening assays, but no further increase was observed in the bic1 bic2 double mutants. On the other hand, in root elongation assays, ABA sensitivity was decreased in the transgenic plants overexpressing BIC2, as well as the bic2 single mutants, but no further decrease was observed in the bic1 bic2 double mutants. By using qRT-PCR (quantitative RT-PCR), we further examined how BIC2 may regulate ABA responses in Arabidopsis , and found that inhibition of ABA on the expression of the ABA receptor genes PYL4 (PYR1-Like 4) and PYL5 were decreased, but promotion of ABA on the expression of the protein kinase gene SnRK2.6 (SNF1-Related Protein Kinases 2.6) was enhanced in both the bic1 bic2 double mutants and 35S:BIC2 overexpression transgenic plants. Taken together, our results suggest that BIC2 regulates ABA responses in Arabidopsis possibly by affecting the expression of ABA signaling key regulator genes.

Comparative transcriptomic analysis of transcription factors and hormones during flower bud differentiation in 'Red Globe' grape under red‒blue light

Grape is a globally significant fruit-bearing crop, and the grape flower bud differentiation essential to fruit production is closely related to light quality. To investigate the regulatory mechanism of grape flower bud differentiation under red‒blue light, the transcriptome and hormone content were determined at four stages of flower bud differentiation. The levels of indole-3-acetic acid (IAA) and abscisic acid (ABA) in grape flower buds at all stages of differentiation under red‒blue light were higher than those in the control. However, the levels of cytokinins (CKs) and gibberellic acid (giberellins, GAs) fluctuated continuously over the course of flower bud differentiation. Moreover, many differentially expressed genes were involved in auxin, CK, GA, and the ABA signal transduction pathways. There were significant differences in the AUX/IAA, SAUR, A-RR, and ABF gene expression levels between the red‒blue light treatment and the control buds, especially in regard to the ABF genes, the expression levels of which were completely different between the two groups. The expression of GBF4 and AI5L2 in the control was always low, while the expression under red‒blue light increased. AI5L7 and AI5L5 expression levels showed an upwards trend in the control plant buds and gradually decreased in red‒blue light treatment plant buds. Through weighted gene coexpression network analysis, we determined that the transcription factors WRK48 (WRKY family), EF110 (ERF family), ABR1, CAMTA3 (CAMTA family), and HSFA3 (HSF family) may be involved in the regulation of the GBF4 gene. This study lays a foundation for further analysis of grape flower bud differentiation regulation under red‒blue light.

Molecular Bases of Signaling Processes Regulated by Cryptochrome Sensory Photoreceptors in Plants

The blue-light sensors, cryptochromes, compose the extensive class of flavoprotein photoreceptors, regulating signaling processes in plants underlying their development, growth, and metabolism. In several algae, cryptochromes may act not only as sensory photoreceptors but also as photolyases, catalyzing repair of the UV-induced DNA lesions. Cryptochromes bind FAD as the chromophore at the photolyase homologous region (PHR) domain and contain the cryptochrome C-terminal extension (CCE), which is absent in photolyases. Photosensory process in cryptochrome is initiated by photochemical chromophore conversions, including formation of the FAD redox forms. In the state with the chromophore reduced to neutral radical (FADH×), the photoreceptor protein undergoes phosphorylation, conformational changes, and disengagement from the PHR domain and CCE with subsequent formation of oligomers of cryptochrome molecules. Photooligomerization is a structural basis of the functional activities of cryptochromes, since it ensures formation of their complexes with a variety of signaling proteins, including transcriptional factors and regulators of transcription. Interactions in such complexes change the protein signaling activities, leading to regulation of gene expression and plant photomorphogenesis. In recent years, multiple papers, reporting novel, more detailed information about the molecular mechanisms of above-mentioned processes were published. The present review mainly focuses on analysis of the data contained in these publications, particularly regarding structural aspects of the cryptochrome transitions into photoactivated states and regulatory signaling processes mediated by the cryptochrome photoreceptors in plants.

Insights into cryptochrome modulation of ABA signaling to mediate dormancy regulation in Marchantia polymorpha

The acquisition of dormancy capabilities has enabled plants to survive in adverse terrestrial environmental conditions. Dormancy accumulation and release is coupled with light signaling, which is well studied in Arabidopsis, but it is unclear in the distant nonvascular relative. We study the characteristics and function on dormancy regulation of a blue light receptor cryptochrome in Marchantia polymorpha (MpCRY). Here, we identified MpCRY via bioinformatics and mutant complement analysis. The biochemical characteristics were assessed by multiple protein-binding assays. The function of MpCRY in gemma dormancy was clarified by overexpression and mutation of MpCRY, and its mechanism was analyzed via RNA sequencing and quantitative PCR analyses associated with hormone treatment. We found that the unique MpCRY protein in M. polymorpha undergoes both blue light-promoted interaction with itself (self-interaction) and blue light-dependent phosphorylation. MpCRY has the specific characteristics of blue light-induced nuclear localization and degradation. We further demonstrated that MpCRY transcriptionally represses abscisic acid (ABA) signaling-related gene expression to suppress gemma dormancy, which is dependent on blue light signaling. Our findings indicate that MpCRY possesses specific biochemical and molecular characteristics, and modulates ABA signaling under blue light conditions to regulate gemma dormancy in M. polymorpha.

Shade avoidance syndrome in soybean and ideotype toward shade tolerance

The shade avoidance syndrome (SAS) in soybean can have destructive effects on yield, as essential carbon resources reserved for yield are diverted to the petiole and stem for exaggerated elongation, resulting in lodging and susceptibility to disease. Despite numerous attempts to reduce the unfavorable impacts of SAS for the development of cultivars suitable for high-density planting or intercropping, the genetic bases and fundamental mechanisms of SAS remain largely unclear. The extensive research conducted in the model plant Arabidopsis provides a framework for understanding the SAS in soybean. Nevertheless, recent investigations suggest that the knowledge obtained from model Arabidopsis may not be applicable to all processes in soybean. Consequently, further efforts are required to identify the genetic regulators of SAS in soybean for molecular breeding of high-yield cultivars suitable for density farming. In this review, we present an overview of the recent developments in SAS studies in soybean and suggest an ideal planting architecture for shade-tolerant soybean intended for high-yield breeding.

The MOM1 complex recruits the RdDM machinery via MORC6 to establish de novo DNA methylation

MOM1 is an Arabidopsis factor previously shown to mediate transcriptional silencing independent of major DNA methylation changes. Here we found that MOM1 localizes with sites of RNA-directed DNA methylation (RdDM). Tethering MOM1 with artificial zinc finger to unmethylated FWA promoter led to establishment of DNA methylation and FWA silencing. This process was blocked by mutations in components of the Pol V arm of the RdDM machinery, as well as by mutation of MORC6 . We found that at some endogenous RdDM sites, MOM1 is required to maintain DNA methylation and a closed chromatin state. In addition, efficient silencing of newly introduced FWA transgenes was impaired by mutation of MOM1 or mutation of genes encoding the MOM1 interacting PIAL1/2 proteins. In addition to RdDM sites, we identified a group of MOM1 peaks at active chromatin near genes that colocalized with MORC6. These findings demonstrate a multifaceted role of MOM1 in genome regulation.

CRY2 interacts with CIS1 to regulate thermosensory flowering via FLM alternative splicing

Cryptochromes (CRYs) are evolutionarily conserved photolyase-like photoreceptors found in almost all species, including mammals. CRYs regulate transcription by modulating the activity of several transcription factors, but whether and how they affect pre-mRNA processing are unknown. Photoperiod and temperature are closely associated seasonal cues that influence reproductive timing in plants. CRYs mediate photoperiod-responsive floral initiation, but it is largely unknown whether and how they are also involved in thermosensory flowering. We establish here that blue light and CRY2 play critical roles in thermosensory flowering in Arabidopsis thaliana by regulating RNA alternative splicing (AS) to affect protein expression and development. CRY2 INTERACTING SPLICING FACTOR 1 (CIS1) interacts with CRY2 in a blue light-dependent manner and promotes CRY2-mediated thermosensory flowering. Blue light, CRYs, and CISs affect transcriptome-wide AS profiles, including those of FLOWERING LOCUS M (FLM), which is critical for temperature modulation of flowering. Moreover, CIS1 binds to the FLM pre-mRNA to regulate its AS, while CRY2 regulates the RNA-binding activity of CIS1. Thus, blue light regulates thermosensory flowering via a CRY2-CIS1-FLM signaling pathway that links flowering responses to both light and ambient temperature.

A Cryptochrome adopts distinct moon- and sunlight states and functions as sun- versus moonlight interpreter in monthly oscillator entrainment

The moon's monthly cycle synchronizes reproduction in countless marine organisms. The mass-spawning bristle worm Platynereis dumerilii uses an endogenous monthly oscillator set by full moon to phase reproduction to specific days. But how do organisms recognize specific moon phases? We uncover that the light receptor L-Cryptochrome (L-Cry) discriminates between different moonlight durations, as well as between sun- and moonlight. A biochemical characterization of purified L-Cry protein, exposed to naturalistic sun- or moonlight, reveals the formation of distinct sun- and moonlight states characterized by different photoreduction- and recovery kinetics of L-Cry's co-factor Flavin Adenine Dinucleotide. In Platynereis, L-Cry's sun- versus moonlight states correlate with distinct subcellular localizations, indicating different signaling. In contrast, r-Opsin1, the most abundant ocular opsin, is not required for monthly oscillator entrainment. Our work reveals a photo-ecological concept for natural light interpretation involving a "valence interpreter" that provides entraining photoreceptor(s) with light source and moon phase information.

Blue light-induced phosphorylation of Arabidopsis cryptochrome 1 is essential for its photosensitivity

Plants possess two cryptochrome photoreceptors, cryptochrome 1 (CRY1) and cryptochrome 2 (CRY2), that mediate overlapping and distinct physiological responses. Both CRY1 and CRY2 undergo blue light-induced phosphorylation, but the molecular details of CRY1 phosphorylation remain unclear. Here we identify 19 in vivo phosphorylation sites in CRY1 using mass spectrometry and systematically analyze the physiological and photobiochemical activities of CRY1 variants with phosphosite substitutions. We demonstrate that nonphosphorylatable CRY1 variants have impaired phosphorylation, degradation, and physiological functions, whereas phosphomimetic variants mimic the physiological functions of phosphorylated CRY1 to constitutively inhibit hypocotyl elongation. We further demonstrate that phosphomimetic CRY1 variants exhibit enhanced interaction with the E3 ubiquitin ligase COP1 (CONSTITUTIVELY PHOTOMORPHOGENIC 1). This finding is consistent with the hypothesis that phosphorylation of CRY1 is required for COP1-dependent signaling and regulation of CRY1. We also determine that PHOTOREGULATORY PROTEIN KINASEs (PPKs) phosphorylate CRY1 in a blue light-dependent manner and that this phosphorylation is critical for CRY1 signaling and regulation. These results indicate that, similar to CRY2, blue light-dependent phosphorylation of CRY1 determines its photosensitivity.

UBP12 and UBP13 deubiquitinases destabilize the CRY2 blue light receptor to regulate Arabidopsis growth

Light is a crucial exogenous signal sensed by cryptochrome (CRY) blue light receptors to modulate growth and the circadian clock in plants and animals. However, how CRYs interpret light quantity to regulate growth in plants remains poorly understood. Furthermore, CRY2 protein levels and activity are tightly regulated in light to fine-tune hypocotyl growth; however, details of the mechanisms that explain precise control of CRY2 levels are not fully understood. We show that in Arabidopsis, UBP12 and UBP13 deubiquitinases physically interact with CRY2 in light. UBP12/13 negatively regulates CRY2 by promoting its ubiquitination and turnover to modulate hypocotyl growth. Growth and development were explicitly affected in blue light when UBP12/13 were disrupted or overexpressed, indicating their role alongside CRY2. UBP12/13 also interacted with and stabilized COP1, which is partially required for CRY2 turnover. Our combined genetic and molecular data support a mechanistic model in which UBP12/13 interact with CRY2 and COP1, leading to the stabilization of COP1. Stabilized COP1 then promotes the ubiquitination and degradation of CRY2 under blue light. Despite decades of studies on deubiquitinases, the knowledge of how their activity is regulated is limited. Our study provides insight into how exogenous signals and ligands, along with their receptors, regulate deubiquitinase activity by protein-protein interaction. Collectively, our results provide a framework of cryptochromes and deubiquitinases to detect and interpret light signals to control plant growth at the most appropriate time.

Plant optogenetics: Applications and perspectives

To understand cell biological processes, like signalling pathways, protein movements, or metabolic processes, precise tools for manipulation are desired. Optogenetics allows to control cellular processes by light and can be applied at a high temporal and spatial resolution. In the last three decades, various optogenetic applications have been developed for animal, fungal, and prokaryotic cells. However, using optogenetics in plants has been difficult due to biological and technical issues, like missing cofactors, the presence of endogenous photoreceptors, or the necessity of light for photosynthesis, which potentially activates optogenetic tools constitutively. Recently developed tools overcome these limitations, making the application of optogenetics feasible also in plants. Here, we highlight the most useful recent applications in plants and give a perspective for future optogenetic approaches in plants science.

The RALF1-FERONIA complex interacts with and activates TOR signaling in response to low nutrients

Target of rapamycin (TOR) kinase is an evolutionarily conserved major regulator of nutrient metabolism and organismal growth in eukaryotes. In plants, nutrients are remobilized and reallocated between shoots and roots under low-nutrient conditions, and nitrogen and nitrogen-related nutrients (e.g., amino acids) are key upstream signals leading to TOR activation in shoots under low-nutrient conditions. However, how these forms of nitrogen can be sensed to activate TOR in plants is still poorly understood. Here we report that the Arabidopsis receptor kinase FERONIA (FER) interacts with the TOR pathway to regulate nutrient (nitrogen and amino acid) signaling under low-nutrient conditions and exerts similar metabolic effects in response to nitrogen deficiency. We found that FER and its partner, RPM1-induced protein kinase (RIPK), interact with the TOR/RAPTOR complex to positively modulate TOR signaling activity. During this process, the receptor complex FER/RIPK phosphorylates the TOR complex component RAPTOR1B. The RALF1 peptide, a ligand of the FER/RIPK receptor complex, increases TOR activation in the young leaf by enhancing FER-TOR interactions, leading to promotion of true leaf growth in Arabidopsis under low-nutrient conditions. Furthermore, we showed that specific amino acids (e.g., Gln, Asp, and Gly) promote true leaf growth under nitrogen-deficient conditions via the FER-TOR axis. Collectively, our study reveals a mechanism by which the RALF1-FER pathway activates TOR in the plant adaptive response to low nutrients and suggests that plants prioritize nutritional stress response over RALF1-mediated inhibition of cell growth under low-nutrient conditions.

Photoreceptors’ gene expression of Arabidopsis thaliana grown with biophilic LED-sourced lighting systems

Using specific photoreceptors, plants can sense light signals fundamental to their growth and development under changing light conditions. Phytochromes sense red and far-red light, cryptochromes and phototropins sense UV-A and blue light, while the UVR8 gene senses UV-B signals. The study of the molecular mechanisms used by plants to respond to artificial biophilic lighting is of pivotal importance for the implementation of biophilic approaches in indoor environments. CoeLux® is a new lighting system that reproduces the effect of natural sunlight entering through an opening in the ceiling, with a realistic sun perceived at an infinite distance surrounded by a clear blue sky. We used the model plant Arabidopsis thaliana to assess the gene expression of the main plant photoreceptors at different light intensities and at different times after exposure to the CoeLux® light type, using high-pressure sodium (HPS) lamps as control light type. Genes belonging to different families of photoreceptors showed a similar expression pattern, suggesting the existence of a common upstream regulation of mRNA transcription. In particular, PHYA, PHYC, PHYD, CRY1, CRY2, PHOT1, and UVR8, showed a common expression pattern with marked differences between the two light types applied; under the HPS light type, the expression levels are raising with the decrease of light intensity, while under the CoeLux® light type, the expression levels remain nearly constant at a high fold. Moreover, we showed that under biophilic illumination the light spectrum plays a crucial role in the response of plants to light intensity, both at the molecular and morphological levels.

Two light sensors decode moonlight versus sunlight to adjust a plastic circadian/circalunidian clock to moon phase

The moon provides highly reliable time information to organisms. Whereas sunlight is known to set daily animal timing systems, mechanistic insight into the impact of moonlight on such systems remains scarce. We establish that the marine bristleworm Platynereis dumerilii times the precise hours of mass spawning by integrating lunar light information into a plastic daily timing system able to run with circadian (∼24 h) or circalunidian (∼24.8 h) periodicity. The correct interpretation of moonlight is mediated by the interplay of two light sensors: a cryptochrome and a melanopsin ortholog provide information on light valence and moonrise time, respectively. Besides its ecological relevance, our work provides a plausible explanation for long-standing observations of light intensity–dependent differences in circadian clock periods.

Many species synchronize their physiology and behavior to specific hours. It is commonly assumed that sunlight acts as the main entrainment signal for ∼24-h clocks. However, the moon provides similarly regular time information. Consistently, a growing number of studies have reported correlations between diel behavior and lunidian cycles. Yet, mechanistic insight into the possible influences of the moon on ∼24-h timers remains scarce. We have explored the marine bristleworm Platynereis dumerilii to investigate the role of moonlight in the timing of daily behavior. We uncover that moonlight, besides its role in monthly timing, also schedules the exact hour of nocturnal swarming onset to the nights’ darkest times. Our work reveals that extended moonlight impacts on a plastic clock that exhibits <24 h (moonlit) or >24 h (no moon) periodicity. Abundance, light sensitivity, and genetic requirement indicate that the Platynereis light receptor molecule r-Opsin1 serves as a receptor that senses moonrise, whereas the cryptochrome protein L-Cry is required to discriminate the proper valence of nocturnal light as either moonlight or sunlight. Comparative experiments in Drosophila suggest that cryptochrome’s principle requirement for light valence interpretation is conserved. Its exact biochemical properties differ, however, between species with dissimilar timing ecology. Our work advances the molecular understanding of lunar impact on fundamental rhythmic processes, including those of marine mass spawners endangered by anthropogenic change.

Arabidopsis cryptochrome 2 forms photobodies with TCP22 under blue light and regulates the circadian clock

Cryptochromes are blue light receptors that regulate plant growth and development. They also act as the core components of the central clock oscillator in animals. Although plant cryptochromes have been reported to regulate the circadian clock in blue light, how they do so is unclear. Here we show that Arabidopsis cryptochrome 2 (CRY2) forms photobodies with the TCP22 transcription factor in response to blue light in plant cells. We provide evidence that PPK kinases influence the characteristics of these photobodies and that together these components, along with LWD transcriptional regulators, can positively regulate the expression of CCA1 encoding a central component of the circadian oscillator.

Cryptochrome signaling has been reported to regulate circadian oscillations in plants. Here the authors show that CRY2 and the TCP22 transcription factors can form photobodies in a blue light dependent manner and induce expression of CCA1, a core component of the circadian oscillator.

Arabidopsis cryptochrome 1 undergoes COP1 and LRBs-dependent degradation in response to high blue light

Arabidopsis cryptochrome 1 (CRY1) is an important blue light photoreceptor that promotes photomorphogenesis under blue light. The blue light photoreceptors CRY2 and phototropin 1, and the red/far-red light photoreceptors phytochromes B and A undergo degradation in response to blue and red light, respectively. This study investigated whether and how CRY1 might undergo degradation in response to high-intensity blue light (HBL). We demonstrated that CRY1 is ubiquitinated and degraded through the 26S proteasome pathway in response to HBL. We found that the E3 ubiquitin ligase constitutive photomorphogenic 1 (COP1) is involved in mediating HBL-induced ubiquitination and degradation of CRY1. We also found that the E3 ubiquitin ligases LRBs physically interact with CRY1 and are also involved in mediating CRY1 ubiquitination and degradation in response to HBL. We further demonstrated that blue-light inhibitor of cryptochromes 1 interacts with CRY1 in a blue-light-dependent manner to inhibit CRY1 dimerization/oligomerization, leading to the repression of HBL-induced degradation of CRY1. Our findings indicate that the regulation of CRY1 stability in HBL is coordinated by COP1 and LRBs, which provides a mechanism by which CRY1 attenuates its own signaling and optimizes photomorphogenesis under HBL.

Differential photoregulation of the nuclear and cytoplasmic CRY1 in Arabidopsis

Arabidopsis cryptochrome 1 (CRY1) is a blue light receptor distributed in the nucleus and cytoplasm. The nuclear CRY1, but not cytoplasmic CRY1, mediates blue light inhibition of hypocotyl elongation. However, the photobiochemical mechanisms distinguishing the CRY1 protein in the two subcellular compartments remains unclear. Here we show that the nuclear CRY1, but not the cytoplasmic CRY1, is regulated by phosphorylation, polyubiquitination and 26S proteasome-dependent proteolysis in response to blue light. The blue light-dependent CRY1 degradation is observed only under high fluences of blue light. The nuclear specificity and high fluence dependency of CRY1 explain why this photochemical regulatory mechanism of CRY1 was not observed previously and it further supports the hypothesis that CRY1 is a high light receptor regulating photomorphogenesis. We further show that the nuclear CRY1, but not cytoplasmic CRY1, undergoes blue light-dependent phosphorylation by photoregulatory protein kinase 1 (PPK1) followed by polyubiquitination by the E3 ubiquitin ligase Cul4^COP1/SPAs , resulting in the blue light-dependent proteolysis. Both phosphorylation and ubiquitination of nuclear CRY1 are inhibited by blue-light inhibitor of cryptochromes 1 (BIC1), demonstrating the involvement of photo-oligomerization of the nuclear CRY1. These finding reveals a photochemical mechanism that differentially regulates the physiological activity of the CRY1 photoreceptor in distinct subcellular compartments.

The C-terminus of a diatom plant-like cryptochrome influences the FAD redox state and binding of interaction partners

A plant-like cryptochrome of diatom microalgae, CryP, acts as a photoreceptor involved in transcriptional regulation. It contains FAD and 5,10-methenyltetrahydrofolate as chromophores. Here, we demonstrate that the unstructured C-terminal extension (CTE) of CryP has an influence on the redox state of the flavin. In CryP lacking the CTE, the flavin is in the oxidized state (FADox), whereas it is a neutral radical (FADH•) in the full-length protein. When the CTE of CryP is coupled to another diatom cryptochrome that naturally binds FADox, this chimera also binds FADH•. In full-length CryP, FADH• is the most stable redox state and oxidation to FADox is extremely slow, whereas reduction to FADH2 is reversible in the dark in approximately 1 h. We also identified novel interaction partners of this algal CRY and characterized two of them in depth regarding their binding activities. BolA, a putative transcription factor, binds to monomeric and to dimeric CryP via the CTE, independent of the redox state of the flavin. In contrast, an unknown protein, ID42612, which occurs solely in heterokont algae, binds only to CryP dimers. This binding is independent of the CTE and shows slight differences in strength depending on the flavin's redox state.

MicroProteins: Dynamic and accurate regulation of protein activity

Proteins usually assemble oligomers or high-order complexes to increase their efficiency and specificity in biological processes. The dynamic equilibrium of complex formation and disruption imposes reversible regulation of protein function. MicroProteins are small, single-domain proteins that directly bind target protein complexes and disrupt their assembly. Growing evidence shows that microProteins are efficient regulators of protein activity at the post-translational level. In the last few decades, thousands of plant microProteins have been predicted by computational approaches, but only a few have been experimentally validated. Recent studies highlighted the mechanistic working modes of newly-identified microProteins in Arabidopsis and other plant species. Here, we review characterized microProteins, including their biological roles, regulatory targets, and modes of action. In particular, we focus on microProtein-directed allosteric modulation of key components in light signaling pathways, and we summarize the biogenesis and evolutionary trajectory of known microProteins in plants. Understanding the regulatory mechanisms of microProteins is an important step towards potential utilization of microProteins as versatile biotechnological tools in crop bioengineering.

The Function and Photoregulatory Mechanisms of Cryptochromes From Moso Bamboo (Phyllostachys edulis)

Light is one of the most important environmental factors affecting growth and geographic distribution of forestry plants. Moso bamboo is the largest temperate bamboo on earth and an important non-woody forestry species that serves not only important functions in the economy of rural areas but also carbon sequestration in the world. Due to its decades-long reproductive timing, the germplasm of moso bamboo cannot be readily improved by conventional breeding methods, arguing for a greater need to study the gene function and regulatory mechanisms of this species. We systematically studied the photoregulatory mechanisms of the moso bamboo (Phyllostachys edulis) cryptochrome 1, PheCRY1. Our results show that, similar to its Arabidopsis counterpart, the bamboo PheCRY1s are functionally restricted to the blue light inhibition of cell elongation without an apparent activity in promoting floral initiation. We demonstrate that PheCRY1s undergo light-dependent oligomerization that is inhibited by PheBIC1s, and light-dependent phosphorylation that is catalyzed by PhePPKs. We hypothesize that light-induced phosphorylation of PheCRY1s facilitate their degradation, which control availability of the PheCRY1 proteins and photosensitivity of bamboo plants. Our results demonstrate the evolutionary conservation of not only the function but also photoregulatory mechanism of PheCRY1 in this monocot forestry species.

Stop CRYing! Inhibition of cryptochrome function by small proteins

Plants can detect the presence of light using specialised photoreceptor proteins. These photoreceptors measure the intensity of light, but they can also respond to different spectra of light and thus ‘see' different colours. Cryptochromes, which are also present in animals, are flavin-based photoreceptors that enable plants to detect blue and ultraviolet-A (UV-A) light. In Arabidopsis, there are two cryptochromes, CRYPTOCHROME 1 (CRY1) and CRYPTOCHROME 2 (CRY2) with known sensory roles. They function in various processes such as blue-light mediated inhibition of hypocotyl elongation, photoperiodic promotion of floral initiation, cotyledon expansion, anthocyanin production, and magnetoreception, to name a few. In the dark, the cryptochromes are in an inactive monomeric state and undergo photochemical and conformational change in response to illumination. This results in flavin reduction, oligomerisation, and the formation of the ‘cryptochrome complexome'. Mechanisms of cryptochrome activation and signalling have been extensively studied and found to be conserved across phylogenetic lines. In this review, we will therefore focus on a far lesser-known mechanism of regulation that is unique to plant cryptochromes. This involves inhibition of cryptochrome activity by small proteins that prevent its dimerisation in response to light. The resulting inhibition of function cause profound alterations in economically important traits such as plant growth, flowering, and fruit production. This review will describe the known mechanisms of cryptochrome activation and signalling in the context of their modulation by these endogenous and artificial small inhibitor proteins. Promising new applications for biotechnological and agricultural applications will be discussed.

Signaling Mechanisms by Arabidopsis Cryptochromes

Cryptochromes (CRYs) are blue light photoreceptors that regulate growth, development, and metabolism in plants. In Arabidopsis thaliana (Arabidopsis), CRY1 and CRY2 possess partially redundant and overlapping functions. Upon exposure to blue light, the monomeric inactive CRYs undergo phosphorylation and oligomerization, which are crucial to CRY function. Both the N- and C-terminal domains of CRYs participate in light-induced interaction with multiple signaling proteins. These include the COP1/SPA E3 ubiquitin ligase, several transcription factors, hormone signaling intermediates and proteins involved in chromatin-remodeling and RNA N6 adenosine methylation. In this review, we discuss the mechanisms of Arabidopsis CRY signaling in photomorphogenesis and the recent breakthroughs in Arabidopsis CRY research.

Optophysiology: Illuminating cell physiology with optogenetics

Optogenetics combines light and genetics to enable precise control of living cells, tissues, and organisms with tailored functions. Optogenetics has the advantages of noninvasiveness, rapid responsiveness, tunable reversibility, and superior spatiotemporal resolution. Following the initial discovery of microbial opsins as light-actuated ion channels, a plethora of naturally occurring or engineered photoreceptors or photosensitive domains that respond to light at varying wavelengths has ushered in the next chapter of optogenetics. Through protein engineering and synthetic biology approaches, genetically-encoded photoswitches can be modularly engineered into protein scaffolds or host cells to control a myriad of biological processes, as well as to enable behavioral control and disease intervention in vivo. Here, we summarize these optogenetic tools on the basis of their fundamental photochemical properties to better inform the chemical basis and design principles. We also highlight exemplary applications of opsin-free optogenetics in dissecting cellular physiology (designated "optophysiology"), and describe the current progress, as well as future trends, in wireless optogenetics, which enables remote interrogation of physiological processes with minimal invasiveness. This review is anticipated to spark novel thoughts on engineering next-generation optogenetic tools and devices that promise to accelerate both basic and translational studies.

Dynamics and mechanism of dimer dissociation of photoreceptor UVR8

Photoreceptors are a class of light-sensing proteins with critical biological functions. UVR8 is the only identified UV photoreceptor in plants and its dimer dissociation upon UV sensing activates UV-protective processes. However, the dissociation mechanism is still poorly understood. Here, by integrating extensive mutations, ultrafast spectroscopy, and computational calculations, we find that the funneled excitation energy in the interfacial tryptophan (Trp) pyramid center drives a directional Trp-Trp charge separation in 80 ps and produces a critical transient Trp anion, enabling its ultrafast charge neutralization with a nearby positive arginine residue in 17 ps to destroy a key salt bridge. A domino effect is then triggered to unzip the strong interfacial interactions, which is facilitated through flooding the interface by channel and interfacial water molecules. These detailed dynamics reveal a unique molecular mechanism of UV-induced dimer monomerization.

Transcriptomic and Metabolomic Profiling Reveals the Effect of LED Light Quality on Fruit Ripening and Anthocyanin Accumulation in Cabernet Sauvignon Grape

Different light qualities have various impacts on the formation of fruit quality. The present study explored the influence of different visible light spectra (red, green, blue, and white) on the formation of quality traits and their metabolic pathways in grape berries. We found that blue light and red light had different effects on the berries. Compared with white light, blue light significantly increased the anthocyanins (malvidin-3-O-glucoside and peonidin-3-O-glucoside), volatile substances (alcohols and phenols), and soluble sugars (glucose and fructose), reduced the organic acids (citric acid and malic acid), whereas red light achieved the opposite effect. Transcriptomics and metabolomics analyses revealed that 2707, 2547, 2145, and 2583 differentially expressed genes (DEGs) and (221, 19), (254, 22), (189, 17), and (234, 80) significantly changed metabolites (SCMs) were filtered in the dark vs. blue light, green light, red light, and white light, respectively. According to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses, most of the DEGs identified were involved in photosynthesis and biosynthesis of flavonoids and flavonols. Using weighted gene co-expression network analysis (WGCNA) of 23410 highly expressed genes, two modules significantly related to anthocyanins and soluble sugars were screened out. The anthocyanins accumulation is significantly associated with increased expression of transcription factors (VvHY5, VvMYB90, VvMYB86) and anthocyanin structural genes (VvC4H, Vv4CL, VvCHS3, VvCHI1, VvCHI2, VvDFR), while significantly negatively correlated with VvPIF4. VvISA1, VvISA2, VvAMY1, VvCWINV, VvβGLU12, and VvFK12 were all related to starch and sucrose metabolism. These findings help elucidate the characteristics of different light qualities on the formation of plant traits and can inform the use of supplemental light in the field and after harvest to improve the overall quality of fruit.

GmBICs Modulate Low Blue Light-Induced Stem Elongation in Soybean

Blue-light inhibitors of cryptochromes (BICs) promote hypocotyl elongation by suppressing the activity of cryptochromes in Arabidopsis. Nevertheless, the roles of BICs in other plant species are still unclear. Here we investigate their functions by genetic overexpression and CRISPR/Cas9 engineered mutations targeting the six GmBIC genes in soybean. We showed that the GmBICs overexpression (GmBICs-OX) lines strongly promoted stem elongation, while the single, double, and quadruple mutations in the GmBIC genes resulted in incremental dwarfing phenotypes. Furthermore, overexpression of GmBIC2a abolished the low blue light (LBL)-induced stem elongation, demonstrating the involvement of GmBICs in regulating cryptochrome-mediated LBL-induced shade avoidance syndrome (SAS). The Gmbic1a1b2a2b quadruple mutant displayed reduced stem elongation under LBL conditions, which was reminiscent of the GmCRY1b-OX lines. Taken together, this study provided essential genetic resources for elucidating GmBICs functional mechanisms and breeding of shade-tolerant soybean cultivars in future.

Modulation of spatiotemporal dynamics in the bromate–sulfite–ferrocyanide reaction system by visible light

We have carried out the first systematic study of the effects of visible light on the homogenous dynamics in the bromate–sulfite–ferrocyanide (BSF) reaction. Under flow conditions, the reaction system displayed photoinduction and photoinhibition behavior, and the oscillatory period decreased with the increase of light intensity, which is due to the fact that light irradiation mainly enhanced the negative process and affected the positive feedback. The light effect on positive and negative feedback is studied by analyzing the period length of pH increasing and decreasing in detail. With the increase of light intensity, the period length of pH increasing decreases monotonically, while the period length of pH decreasing changes nonmonotonically. These results suggest that light could be used as a powerful tool to control homogenous dynamics. Results obtained from numerical simulations are in good agreement with experimental data.

The BSF reaction system displayed photoinduction and photoinhibition behavior under flow conditions. The oscillatory period decreased as the light irradiation mainly enhanced the negative process and affected the positive feedback.

OsBIC1 Directly Interacts with OsCRYs to Regulate Leaf Sheath Length through Mediating GA-Responsive Pathway

Cryptochrome 1 and 2 (CRY1 and CRY2) are blue light receptors involved in the regulation of hypocotyl elongation, cotyledon expansion, and flowering time in Arabidopsisthaliana. Two cryptochrome-interacting proteins, Blue-light Inhibitor of Cryptochrome 1 and 2 (BIC1 and BIC2), have been found in Arabidopsis. BIC1 plays critical roles in suppressing the physiological activities of CRY2, which include the blue light-dependent dimerization, phosphorylation, photobody formation, and degradation process, but the functional characterization of BIC protein in other crops has not yet been performed. To investigate the function of BIC protein in rice (Oryza sativa), two homologous genes of Arabidopsis BIC1 and BIC2, namely OsBIC1 and OsBIC2 (OsBICs), were identified. The overexpression of OsBIC1 and OsBIC2 led to increased leaf sheath length, whereas mutations in OsBIC1 displayed shorter leaf sheath in a blue light intensity-dependent manner. OsBIC1 regulated blue light-induced leaf sheath elongation through direct interaction with OsCRY1a, OsCRY1b, and OsCRY2 (OsCRYs). Longitudinal sections of the second leaf sheath demonstrated that OsBIC1 and OsCRYs controlled leaf sheath length by influencing the ratio of epidermal cells with different lengths. RNA-sequencing (RNA-seq) and quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) analysis further proved that OsBIC1 and OsCRYs regulated similar transcriptome changes in regulating Gibberellic Acids (GA)-responsive pathway. Taken together, these results suggested that OsBIC1 and OsCRYs worked together to regulate epidermal cell elongation and control blue light-induced leaf sheath elongation through the GA-responsive pathway.

Functions of COP1/SPA E3 Ubiquitin Ligase Mediated by MpCRY in the Liverwort Marchantia polymorpha under Blue Light

COP1/SPA1 complex in Arabidopsis inhibits photomorphogenesis through the ubiquitination of multiple photo-responsive transcription factors in darkness, but such inhibiting function of COP1/SPA1 complex would be suppressed by cryptochromes in blue light. Extensive studies have been conducted on these mechanisms in Arabidopsis whereas little attention has been focused on whether another branch of land plants bryophyte utilizes this blue-light regulatory pathway. To study this problem, we conducted a study in the liverwort Marchantia polymorpha and obtained a MpSPA knock-out mutant, in which Mpspa exhibits the phenotype of an increased percentage of individuals with asymmetrical thallus growth, similar to MpCRY knock-out mutant. We also verified interactions of MpSPA with MpCRY (in a blue light-independent way) and with MpCOP1. Concomitantly, both MpSPA and MpCOP1 could interact with MpHY5, and MpSPA can promote MpCOP1 to ubiquitinate MpHY5 but MpCRY does not regulate the ubiquitination of MpHY5 by MpCOP1/MpSPA complex. These data suggest that COP1/SPA ubiquitinating HY5 is conserved in Marchantia polymorpha, but dissimilar to CRY in Arabidopsis, MpCRY is not an inhibitor of this process under blue light.