COP1 and ELF3 control circadian function and photoperiodic flowering by regulating GI stability

FvbHLH78 interacts with FvCRY2 to promote flowering in woodland strawberry

Flowering is a crucial agricultural trait of strawberries. While the bHLH family comprises numerous members in plants, its function in controlling strawberry flowering remains largely unexplored. In this study, FvbHLH78 was found to be highly expressed in the shoot apices and ripening fruits of woodland strawberry (Fragaria vesca). FvbHLH78 is localized to the nucleus and exhibits self-activating transcriptional properties. Overexpression of FvbHLH78 in woodland strawberry resulted in an early flowering phenotype compared to the control plants. This phenomenon was attributed to FvbHLH78 directly binding to the promoters of the genes associated with flowering, namely FvFT, FvSEP3, FvLFY, and FvAGL42. Moreover, FvbHLH78 interacted with a blue light receptor FvCRY2, which enhances FvbHLH78 promoter-binding affinity to FvFT, FvSEP3, FvLFY, and FvAGL42, thereby accelerating flowering. Collectively, these findings demonstrate that the FvbHLH78-FvCRY2 complex in strawberries acts as an enhancer of genes associated with flowering, thereby accelerating the flowering process. These data offer an understanding for enriching the roles of bHLH78 and accelerating flowering in strawberry.

Multilayered roles of COP1 in plant growth and stress responses

COP1 (CONSTITUTIVE PHOTOMORPHOGENIC 1) is a highly conserved eukaryotic protein that functions as a central repressor in plant photomorphogenesis. As an E3 ubiquitin ligase, COP1 regulates various physiological processes by ubiquitinating and degrading specific substrates. In recent years, the multifunctionality of COP1 has garnered increasing attention, as it not only is involved in light signal transduction but also plays a critical regulatory role in plant growth and development, stress response pathways, and hormone signaling networks. Moreover, COP1 also participates in the cross-regulation of multiple signaling pathways, including light signaling, stress response, and hormone signaling, further highlighting its core position in plant environment adaptation and growth and development. This review systematically elaborates on the evolutionary conservation, structural features, and multifunctionality of COP1, with a focus on summarizing its molecular regulatory networks in growth, development, and stress responses, while exploring its potential applications in crop genetic improvement.

The chromosome-scale genomes of two cultivated safflowers (Carthamus tinctorius) provide insights into the genetic diversity resulting from domestication

KEY MESSAGE

Two cultivated safflowers from distinct areas elucidate the genetic diversity present in the linoleic acid biosynthesis, flowering time and flavonoid biosynthesis. The process of domestication facilitates the adaptation of crops to agricultural environments. In this study, we selected two representative safflower cultivars that has been domesticated in two distinct areas in China as samples to investigate their genetic diversity due to local environmental adaption. Yunhong-7 is a locally bred safflower (Carthamus tinctorius) cultivar, that has been currently widely cultivated in Yunnan Province, Southwest China, and Anhui-1 is a safflower cultivar that was locally bred in Anhui Province, East China. We firstly generated the chromosome-scale genome assembly for yunhong-7 cultivar by combining PacBio and Hi-C technologies. Through comparative genomic analysis, we identified structural variations (SVs) between yunhong-7 and anhui-1, which revealed their genetic differences in the pathways of fatty acid biosynthesis, circadian rhythm and flavonoid biosynthesis. Subsequently, a total of 40 non-redundant fatty acid desaturase 2 (FAD2) genes (39 for yunhong-7 and 20 for anhui-1) were identified, revealing the presence of copy-number variation and major genes change between yunhong-7 and anhui-1. The presented results suggested that changes in SVs may induce alterations in the expression of flowering-related genes, which could explain the observed early flowering phenotype in yunhong-7 compared to anhui-1. We identified a total of 197 non-redundant UDP-glucuronosyltransferases (UGT) genes. Based on prokaryotic expression system, we investigated the catalytic functions of two unique UGT genes (CtUGT.18 and CtUGT.191). The current study increases our knowledge of genetic diversity among crop cultivars resulting from distinct domestication processes and thus could contribute to the advancement of traits research and the safflower breeding.

ELF3 coordinates temperature and photoperiodic control of seasonal growth in hybrid aspen

Timely growth cessation before winter is crucial for the survival of perennial plants in temperate and boreal regions. Short photoperiod (SP) and low temperature (LT) are major seasonal cues regulating growth cessation. SP, sensed in the leaves, initiates growth cessation by downregulating FLOWERING LOCUS T 2 (FT2) expression, but how LT regulates seasonal growth is unclear. Genetic and cell biological approaches identified a hybrid aspen EARLY FLOWERING 3(ELF3) ortholog with a prion-like domain (PrLD) that undergoes LT-responsive phase separation as a key mediator of LT-induced growth cessation. In contrast with SP, LT acts independently of FT2 downregulation and targets the AIL1-BRC1 transcription factor network and hormonal pathways via ELF3 to induce growth cessation. Intriguingly, ELF3 also functions in SP-mediated growth cessation by downregulating FT2 in leaves. Our work thus reveals a previously unrecognized role of ELF3 in growth cessation and in coordinating temperature and photoperiodic pathways to enable robust adaptation to seasonal change.

Abundant clock proteins point to missing molecular regulation in the plant circadian clock

Understanding the biochemistry behind whole-organism traits such as flowering time is a longstanding challenge, where mathematical models are critical. Very few models of plant gene circuits use the absolute units required for comparison to biochemical data. We refactor two detailed models of the plant circadian clock from relative to absolute units. Using absolute RNA quantification, a simple model predicted abundant clock protein levels in Arabidopsis thaliana, up to 100,000 proteins per cell. NanoLUC reporter protein fusions validated the predicted levels of clock proteins in vivo. Recalibrating the detailed models to these protein levels estimated their DNA-binding dissociation constants (Kd). We estimate the same Kd from multiple results in vitro, extending the method to any promoter sequence. The detailed models simulated the Kd range estimated from LUX DNA-binding in vitro but departed from the data for CCA1 binding, pointing to further circadian mechanisms. Our analytical and experimental methods should transfer to understand other plant gene regulatory networks, potentially including the natural sequence variation that contributes to evolutionary adaptation.

Allelic Variation of Hd17 for Rice Heading Date is Caused by Natural Selection

Heading date is an important agronomic trait of rice, which directly determines adaptability and yield. Selection for natural variated alleles for heading date genes is an important manifestation of rice domestication that allows rice to spread to more broad geographic areas. In this study, three alleles of the Hd17 gene for heading date were identified by sequence analysis of 14 single-segment substitution lines, 6 wild rice species, and 2524 accessions of O. sativa. The Hd17-1 allele is an ancestral type with a middle heading date. The Hd17-2 allele was caused by the functional nucleotide polymorphism (FNP) of C to T at position 1016 of the gene and exhibits delay heading. The Hd17-3 allele was caused by the FNP of C to T in 1673 point of the gene and shows earlier heading. The Hd17-1 allele is mainly distributed in tropical regions, carrying by 5 wild rice species, O. glaberrima, and two O. sativa (Aus/Boro and tropical japonica types). The Hd17-2 allele is mainly distributed in subtropical regions, carrying by O. meridionalis, O. rufipogon, and two O. sativa (indica subspecies and Basmati/Sandri types). The Hd17-3 allele is mainly distributed in temperate regions, carrying only by temperate japonica of O. sativa. Hd17-2 and Hd17-3 had been evolved from Hd17-1, independently. Three different rice growing regions formed three alleles of Hd17, showing that the allelic variation of Hd17 is the result of natural selection. We also found that Hd17 controls heading date by up-regulating Ghd7 and down-regulating Ehd1 under long day conditions. Our findings will help to understand the evolution and the regulation of Hd17 in rice.

The LUX-SWI3C module regulates photoperiod sensitivity in Arabidopsis thaliana

In plants, the photoperiod sensitivity directly influences flowering time, which in turn affects latitudinal adaptation and yield. However, research into the mechanisms underlying photoperiod sensitivity, particularly those mediated by epigenetic regulation, is still in its nascent stages. In this study, we analyzed the regulation of photoperiod sensitivity in Arabidopsis thaliana. We demonstrate that the evening complex LUX ARRYTHMO (LUX) and the chromatin remodeling factor SWITCH/SUCROSE NONFERMENTING 3C (SWI3C) regulate GI locus chromatin compaction and H3K4me3 modification levels at the GIGANTEA locus under different photoperiod conditions. This mechanism is one of the key factors that allow plants to distinguish between long-day and short-day photoperiods. Our study provides insight into how the LUX-SWI3C module regulates photoperiod sensitivity at the epigenetic level.

Molecular genetic regulation of the vegetative-generative transition in wheat from an environmental perspective

The key to the wide geographical distribution of wheat is its high adaptability. One of the most commonly used methods for studying adaptation is investigation of the transition between the vegetative-generative phase and the subsequent intensive stem elongation process. These processes are determined largely by changes in ambient temperature, the diurnal and annual periodicity of daylength, and the composition of the light spectrum. Many genes are involved in the perception of external environmental signals, forming a complex network of interconnections that are then integrated by a few integrator genes. This hierarchical cascade system ensures the precise occurrence of the developmental stages that enable maximum productivity. This review presents the interrelationship of molecular-genetic pathways (Earliness per se, circadian/photoperiod length, vernalization - cold requirement, phytohormonal - gibberellic acid, light perception, ambient temperature perception and ageing - miRNA) responsible for environmental adaptation in wheat. Detailed molecular genetic mapping of wheat adaptability will allow breeders to incorporate new alleles that will create varieties best adapted to local environmental conditions.

Research progress on delayed flowering under short-day condition in Arabidopsis thaliana

Flowering represents a pivotal phase in the reproductive and survival processes of plants, with the photoperiod serving as a pivotal regulator of plant-flowering timing. An investigation of the mechanism of flowering inhibition in the model plant Arabidopsis thaliana under short-day (SD) conditions will facilitate a comprehensive approach to crop breeding for flowering time, reducing or removing flowering inhibition, for example, can extend the range of adaptation of soybean to high-latitude environments. In A. thaliana, CONSTANS (CO) is the most important component for promoting flowering under long-day (LD) conditions. However, CO inhibited flowering under the SD conditions. Furthermore, the current studies revealed that A. thaliana delayed flowering through multiple pathways that inhibit the transcription and sensitivity of FLOWERING LOCUS T (FT) and suppresses the response to, or synthesis of, gibberellins (GA) at different times, for potential crop breeding resources that can be explored in both aspects. However, the underlying mechanism remains poorly understood. In this review, we summarized the current understanding of delayed flowering under SD conditions and discussed future directions for related topics.

The Regulatory-associated protein of target of rapamycin 1B (RAPTOR 1B) interconnects with the photoperiod pathway to promote flowering in Arabidopsis

The transition from vegetative to reproductive growth, or floral transition, is a tightly regulated, energy-demanding process. In Arabidopsis, the interplay of light perception and circadian rhythms detects changes in photoperiod length, accelerating flowering under long days (LD). CONSTANS (CO), a transcription factor, upregulates FLOWERING LOCUS T (FT) in leaves during dusk. The FT protein then moves to the shoot apical meristem, triggering the floral transition. While light and circadian signals control CO protein levels, less is known about how the nutrients/energy sensing regulates the photoperiod pathway for flowering modulation in this process. In our study, we identify the contribution of the Regulatory-associated protein of target of rapamycin 1B (RAPTOR1B), a component of the nutrient-sensing TOR complex (TORC), in the induction of specific flowering genes under CO control. While transcription of CO remains unaffected in raptor1b mutants, a reduction in its protein levels at dusk is observed compared to the wild type. Remarkably, the mutant also exhibits compromised GIGANTEA (GI) protein levels, crucial for CO stabilization during dusk. Our results indicate that the interaction and colocalization of RAPTOR1B with GI in the nucleus might influence GI levels through an unknown posttranscriptional mechanism. Genetic crosses position RAPTOR1B upstream of CO and GI. This is supported by phenotypic and molecular analyses. Our findings demonstrate that RAPTOR1B, likely as part of TORC, contributes to the photoperiod pathway of the flowering network, ensuring the timely initiation of floral transition under LD conditions.

The molecular basis of CONSTITUTIVE PHOTOMORPHOGENIC1 action during photomorphogenesis

CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1), a repressor of seedling photomorphogenesis, is tightly controlled by light. In Arabidopsis, COP1 primarily acts as a part of large E3 ligase complexes and targets key light-signaling factors for ubiquitination and degradation. Upon light perception, the action of COP1 is precisely modulated by active photoreceptors. During seedling development, light plays a predominant role in modulating seedling morphogenesis, including inhibition of hypocotyl elongation, cotyledon opening and expansion, and chloroplast development. These visible morphological changes evidently result from networks of molecular action. In this review, we summarize current knowledge about the molecular role of COP1 in mediating light-controlled seedling development.

The COP1W467 tryptophan residue in the WD40 domain is essential for light- and temperature-mediated hypocotyl growth and flowering in Arabidopsis

COP1 is the essential protein that integrates various environmental and hormonal cues to control plant growth and development at multiple levels. COP1 is a RING-finger-type E3 ubiquitin ligase that acts as a potent repressor of photomorphogenesis and flowering by targeting numerous substrates for ubiquitination and promoting their proteolysis via the 26S proteasome system. The WD40 repeat domain with conserved amino acid residues was shown to be essential for interacting with its targets. However, the role of these amino acids in regulating hypocotyl growth and flowering in response to varying light and temperatures remains unknown. Here, we show that tryptophan amino acid at the position 467 residue (COP1W467) is relevant in mediating the interaction with its targets to regulate the COP1-mediated proteolysis. The COP1W467 plays a critical role in inducing growth responses in shade light by interacting and degrading HY5, a crucial negative regulator of shade-avoidance response (SAR). Moreover, COP1W467 integrates warm ambient temperature signals to promote hypocotyl growth by increasing PIF4 and decreasing HY5 protein stability. Finally, we found that COP1W467 is important in inhibiting flowering under a short-day photoperiod, likely through interacting with CO for degradation. Together, this study highlights that the COP1W467 residue is essential to regulate seedling photomorphogenesis, SAR, thermomorphogenesis and flowering for the fine adjustment of plant growth and development under dynamic light and temperature conditions.

The AGL6-ELF3-FT circuit controls flowering time in Arabidopsis

Adjusting the timing of floral transition is essential for reproductive success in plants. A number of flowering regulators integrate internal and external signals to precisely determine the time to flower. We here report that the AGAMOUS-LIKE 6 (AGL6) - EARLY FLOWERING 3 (ELF3) module regulates flowering in the FLOWERING LOCUS T (FT)-dependent pathway in Arabidopsis. The AGL6 transcriptional repressor promotes floral transition by directly suppressing ELF3, which in turn directly represses FT expression that acts as a floral integrator. Indeed, ELF3 is epistatic to AGL6 in the control of floral transition. Overall, our findings propose that the AGL6-ELF3 module contributes to fine-tuning flowering time in plants.

A pair of E3 ubiquitin ligases control immunity and flowering by targeting different ELF3 proteins in rice

The ubiquitin-proteasome system (UPS) plays crucial roles in cellular processes including plant growth, development, and stress responses. In this study, we report that a pair of E3 ubiquitin ligases, AvrPiz-t-interaction protein 6 (APIP6) and IPA1-interaction protein 1 (IPI1), intricately target early flowering3 (ELF3) paralogous proteins to control rice immunity and flowering. APIP6 forms homo-oligomers or hetero-oligomers with IPI1. Both proteins interact with OsELF3-2, promoting its degradation to positively control resistance against the rice blast fungus (Magnaporthe oryzae). Intriguingly, overexpression of IPI1 in Nipponbare caused significantly late-flowering phenotypes similar to the oself3-1 mutant. Except for late flowering, oself3-1 enhances resistance against M. oryzae. IPI1 also interacts with and promotes the degradation of OsELF3-1, a paralog of OsELF3-2. Notably, IPI1 and APIP6 synergistically modulate OsELF3s degradation, finely tuning blast disease resistance by targeting OsELF3-2, while IPI1 controls both disease resistance and flowering by targeting OsELF3-1. This study unravels multiple functions for a pair of E3 ligases in rice.

E3 ligase SlCOP1-1 stabilizes transcription factor SlOpaque2 and enhances fruit resistance to Botrytis cinerea in tomato

CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), a pivotal repressor in plant photomorphogenesis, has been extensively studied in various plant processes. However, the specific roles of COP1 in fruit remain poorly understood. Here, we functionally characterized SlCOP1-1 (also known as LeCOP1), an Arabidopsis (Arabidopsis thaliana) COP1 ortholog, in tomato (Solanum lycopersicum) fruit ripening and disease resistance. Despite the clear upregulation of SlCOP1-1 during fruit ripening, knockout or overexpression (OE) of SlCOP1-1 in tomatoes only minimally affected ripening. Intriguingly, these genetic manipulations substantially altered fruit resistance to the fungal pathogen Botrytis cinerea. Proteomic analysis revealed differential accumulation of proteins associated with fruit disease resistance upon SlCOP1-1 knockout or OE. To unravel the mechanism of SlCOP1-1 in disease resistance, we conducted a screen for SlCOP1-1-interacting proteins and identified the stress-related bZIP transcription factor SlOpaque2. We provide evidence that SlOpaque2 functions in tomato resistance to B. cinerea, and SlCOP1-1-mediated mono-ubiquitination and stabilization of SlOpaque2 contributes to fruit resistance against B. cinerea. Our findings uncover a regulatory role of COP1 in controlling fruit disease resistance, enriching our understanding of the regulatory network orchestrating fruit responses to disease.

Manipulation of photosensory and circadian signaling restricts phenotypic plasticity in response to changing environmental conditions in Arabidopsis

Plants exploit phenotypic plasticity to adapt their growth and development to prevailing environmental conditions. Interpretation of light and temperature signals is aided by the circadian system, which provides a temporal context. Phenotypic plasticity provides a selective and competitive advantage in nature but is obstructive during large-scale, intensive agricultural practices since economically important traits (including vegetative growth and flowering time) can vary widely depending on local environmental conditions. This prevents accurate prediction of harvesting times and produces a variable crop. In this study, we sought to restrict phenotypic plasticity and circadian regulation by manipulating signaling systems that govern plants' responses to environmental signals. Mathematical modeling of plant growth and development predicted reduced plant responses to changing environments when circadian and light signaling pathways were manipulated. We tested this prediction by utilizing a constitutively active allele of the plant photoreceptor phytochrome B, along with disruption of the circadian system via mutation of EARLY FLOWERING3. We found that these manipulations produced plants that are less responsive to light and temperature cues and thus fail to anticipate dawn. These engineered plants have uniform vegetative growth and flowering time, demonstrating how phenotypic plasticity can be limited while maintaining plant productivity. This has significant implications for future agriculture in both open fields and controlled environments.

Decoding the plant clock: a review of mathematical models for the circadian regulatory network

Most organisms have evolved specific mechanisms to respond to changes in environmental conditions such as light and temperature over the course of day. These periodic changes in the physiology and behaviour of organisms, referred to as circadian rhythms, are a consequence of intricate molecular mechanisms in the form of transcription and translational feedback loops. The plant circadian regulatory network is a complex web of interconnected feedback loops involving various transcription factors such as CCA1, LHY, PRRs, TOC1, LUX, ELF3, ELF4, RVE8, and more. This network enables plants to adapt and thrive in diverse environmental conditions. It responds to entrainment signals, including light, temperature, and nutrient concentrations and interacts with most of the physiological functions such as flowering, growth and stress response. Mathematical modelling of these gene regulatory networks enables a deeper understanding of not only the function but also the perturbations that may affect the plant growth and function with changing climate. Over the years, numerous mathematical models have been developed to understand the diverse aspects of plant circadian regulation. In this review, we have delved into the systematic development of these models, outlining the model components and refinements over time. We have also highlighted strengths and limitations of each of the models developed so far. Finally, we conclude the review by describing the prospects for investigation and advancement of these models for better understanding of plant circadian regulation.

The E3 ubiquitin ligase COP1 regulates salt tolerance via GIGANTEA degradation in roots

Excess soil salinity significantly impairs plant growth and development. Our previous reports demonstrated that the core circadian clock oscillator GIGANTEA (GI) negatively regulates salt stress tolerance by sequestering the SALT OVERLY SENSITIVE (SOS) 2 kinase, an essential component of the SOS pathway. Salt stress induces calcium-dependent cytoplasmic GI degradation, resulting in activation of the SOS pathway; however, the precise molecular mechanism governing GI degradation during salt stress remains enigmatic. Here, we demonstrate that salt-induced calcium signals promote the cytoplasmic partitioning of CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), leading to the 26S proteasome-dependent degradation of GI exclusively in the roots. Salt stress-induced calcium signals accelerate the cytoplasmic localization of COP1 in the root cells, which targets GI for 26S proteasomal degradation. Align with this, the interaction between COP1 and GI is only observed in the roots, not the shoots, under salt-stress conditions. Notably, the gi-201 cop1-4 double mutant shows an enhanced tolerance to salt stress similar to gi-201, indicating that GI is epistatic to COP1 under salt-stress conditions. Taken together, our study provides critical insights into the molecular mechanisms governing the COP1-mediated proteasomal degradation of GI for salt stress tolerance, raising new possibilities for developing salt-tolerant crops.

How Histone Acetyltransferases Shape Plant Photomorphogenesis and UV Response

Higher plants have developed complex mechanisms to adapt to fluctuating environmental conditions with light playing a vital role in photosynthesis and influencing various developmental processes, including photomorphogenesis. Exposure to ultraviolet (UV) radiation can cause cellular damage, necessitating effective DNA repair mechanisms. Histone acetyltransferases (HATs) play a crucial role in regulating chromatin structure and gene expression, thereby contributing to the repair mechanisms. HATs facilitate chromatin relaxation, enabling transcriptional activation necessary for plant development and stress responses. The intricate relationship between HATs, light signaling pathways and chromatin dynamics has been increasingly understood, providing valuable insights into plant adaptability. This review explores the role of HATs in plant photomorphogenesis, chromatin remodeling and gene regulation, highlighting the importance of chromatin modifications in plant responses to light and various stressors. It emphasizes the need for further research on individual HAT family members and their interactions with other epigenetic factors. Advanced genomic approaches and genome-editing technologies offer promising avenues for enhancing crop resilience and productivity through targeted manipulation of HAT activities. Understanding these mechanisms is essential for developing strategies to improve plant growth and stress tolerance, contributing to sustainable agriculture in the face of a changing climate.

Photoperiod and temperature synergistically regulate heading date and regional adaptation in rice

Plants must accurately integrate external environmental signals with their own development to initiate flowering at the appropriate time for reproductive success. Photoperiod and temperature are key external signals that determine flowering time; both are cyclical and periodic, and they are closely related. In this review, we describe photoperiod-sensitive genes that simultaneously respond to temperature signals in rice (Oryza sativa). We introduce the mechanisms by which photoperiod and temperature synergistically regulate heading date and regional adaptation in rice. We also discuss the prospects for designing different combinations of heading date genes and other cold tolerance or thermo-tolerance genes to help rice better adapt to changes in light and temperature via molecular breeding to enhance yield in the future.

A critical suppression feedback loop determines soybean photoperiod sensitivity

Photoperiod sensitivity is crucial for soybean flowering, adaptation, and yield. In soybean, photoperiod sensitivity centers around the evening complex (EC) that regulates the transcriptional level of the core transcription factor E1, thereby regulating flowering. However, little is known about the regulation of the activity of EC. Our study identifies how E2/GIGANTEA (GI) and its homologs modulate photoperiod sensitivity through interactions with the EC. During long days, E2 interacts with the blue-light receptor flavin-binding, kelch repeat, F box 1 (FKF1), leading to the degradation of J/ELF3, an EC component. EC also suppresses E2 expression by binding to its promoter. This interplay forms a photoperiod regulatory loop, maintaining sensitivity to photoperiod. Disruption of this loop leads to losing sensitivity, affecting soybean's adaptability and yield. Understanding this loop's dynamics is vital for molecular breeding to reduce soybean's photoperiod sensitivity and develop cultivars with better adaptability and higher yields, potentially leading to the creation of photoperiod-insensitive varieties for broader agricultural applications.

Plant cuticles repress organ initiation and development during skotomorphogenesis in Arabidopsis

After germination in the dark, plants produce a shoot apical hook and closed cotyledons to protect the quiescent shoot apical meristem (SAM), which is critical for seedling survival during skotomorphogenesis. The factors that coordinate these processes, particularly SAM repression, remain enigmatic. Plant cuticles, multilayered structures of lipid components on the outermost surface of the aerial epidermis of all land plants, provide protection against desiccation and external environmental stresses. Whether and how cuticles regulate plant development are still unclear. Here, we demonstrate that mutants of BODYGUARD1 (BDG1) and long-chain acyl-CoA synthetase2 (LACS2), key genes involved in cutin biosynthesis, produce a short hypocotyl with an opened apical hook and cotyledons in which the SAM is activated during skotomorphogenesis. Light signaling represses expression of BDG1 and LACS2, as well as cutin biosynthesis. Transcriptome analysis revealed that cuticles are critical for skotomorphogenesis, particularly for the development and function of chloroplasts. Genetic and molecular analyses showed that decreased HOOKLESS1 expression results in apical hook opening in the mutants. When hypoxia-induced expression of LITTLE ZIPPER2 at the SAM promotes organ initiation in the mutants, the de-repressed expression of cell-cycle genes and the cytokinin response induce the growth of true leaves. Our results reveal previously unrecognized developmental functions of the plant cuticle during skotomorphogenesis and demonstrate a mechanism by which light initiates photomorphogenesis through dynamic regulation of cuticle synthesis to induce coordinated and systemic changes in organ development and growth during the skotomorphogenesis-to-photomorphogenesis transition.

Insight from expression profiles of FT orthologs in plants: conserved photoperiodic transcriptional regulatory mechanisms

Floral transition from the vegetative to the reproductive stages is precisely regulated by both environmental and endogenous signals. Among these signals, photoperiod is one of the most important environmental factors for onset of flowering. A florigen, FLOWERING LOCUS T (FT) in Arabidopsis, has thought to be a major hub in the photoperiod-dependent flowering time regulation. Expression levels of FT likely correlates with potence of flowering. Under long days (LD), FT is mainly synthesized in leaves, and FT protein moves to shoot apical meristem (SAM) where it functions and in turns induces flowering. Recently, it has been reported that Arabidopsis grown under natural LD condition flowers earlier than that grown under laboratory LD condition, in which a red (R)/far-red (FR) ratio of light sources determines FT expression levels. Additionally, FT expression profile changes in response to combinatorial effects of FR light and photoperiod. FT orthologs exist in most of plants and functions are thought to be conserved. Although molecular mechanisms underlying photoperiodic transcriptional regulation of FT orthologs have been studied in several plants, such as rice, however, dynamics in expression profiles of FT orthologs have been less spotlighted. This review aims to revisit previously reported but overlooked expression information of FT orthologs from various plant species and classify these genes depending on the expression profiles. Plants, in general, could be classified into three groups depending on their photoperiodic flowering responses. Thus, we discuss relationship between photoperiodic responsiveness and expression of FT orthologs. Additionally, we also highlight the expression profiles of FT orthologs depending on their activities in flowering. Comparative analyses of diverse plant species will help to gain insight into molecular mechanisms for flowering in nature, and this can be utilized in the future for crop engineering to improve yield by controlling flowering time.

What is going on inside of phytochrome B photobodies?

Plants exhibit an enormous phenotypic plasticity to adjust to changing environmental conditions. For this purpose, they have evolved mechanisms to detect and measure biotic and abiotic factors in their surroundings. Phytochrome B exhibits a dual function, since it serves as a photoreceptor for red and far-red light as well as a thermosensor. In 1999, it was first reported that phytochromes not only translocate into the nucleus but also form subnuclear foci upon irradiation by red light. It took more than 10 years until these phytochrome speckles received their name; these foci were coined photobodies to describe unique phytochrome-containing subnuclear domains that are regulated by light. Since their initial discovery, there has been much speculation about the significance and function of photobodies. Their presumed roles range from pure experimental artifacts to waste deposits or signaling hubs. In this review, we summarize the newest findings about the meaning of phyB photobodies for light and temperature signaling. Recent studies have established that phyB photobodies are formed by liquid-liquid phase separation via multivalent interactions and that they provide diverse functions as biochemical hotspots to regulate gene expression on multiple levels.

Disrupting FKF1 homodimerization increases FT transcript levels in the evening by enhancing CO stabilization

KEY MESSAGE

FKF1 dimerization is crucial for proper FT levels to fine-tune flowering time. Attenuating FKF1 homodimerization increased CO abundance by enhancing its COP1 binding, thereby accelerating flowering under long days. In Arabidopsis (Arabidopsis thaliana), the blue-light photoreceptor FKF1 (FLAVIN-BINDING, KELCH REPEAT, F-BOX 1) plays a key role in inducing the expression of FLOWERING LOCUS T (FT), encoding the main florigenic signal in plants, in the late afternoon under long-day conditions (LDs) by forming dimers with FT regulators. Although structural studies have unveiled a variant of FKF1 (FKF1 I160R) that disrupts homodimer formation in vitro, the mechanism by which disrupted FKF1 homodimer formation regulates flowering time remains elusive. In this study, we determined that the attenuation of FKF1 homodimer formation enhances FT expression in the evening by promoting the increased stability of CONSTANS (CO), a primary activator of FT, in the afternoon, thereby contributing to early flowering. In contrast to wild-type FKF1, introducing the FKF1 I160R variant into the fkf1 mutant led to increased FT expression under LDs. In addition, the FKF1 I160R variant exhibited diminished dimerization with FKF1, while its interaction with GIGANTEA (GI), a modulator of FKF1 function, was enhanced under LDs. Furthermore, the FKF1 I160R variant increased the level of CO in the afternoon under LDs by enhancing its binding to COP1, an E3 ubiquitin ligase responsible for CO degradation. These findings suggest that the regulation of FKF1 homodimerization and heterodimerization allows plants to finely adjust FT expression levels around dusk by modulating its interactions with GI and COP1.

Photoperiodic and lighting treatments for flowering control and its genetic regulation in sugarcane breeding

Improvement of sugarcane is hampered due to its narrow genetic base, and the difficulty in synchronizing flowering further hinders the exploitation of the genetic potential of available germplasm resources. Therefore, the continuous evaluation and optimization of flowering control and induction techniques are vital for sugarcane improvement. In view of this, the review was conducted to investigate the current understanding of photoperiodic and lighting treatment effects on sugarcane flowering and its genetic regulation. Photoperiod facilities have made a significant contribution to flowering control in sugarcane; however, inductive photoperiods are still unknown for some genotypes, and some intended crosses are still impossible to produce because of unresponsive varieties. The effectiveness of lower red/far-red ratios in promoting sugarcane flowering has been widely understood. Furthermore, there is vast potential for utilizing blue, red, and far-red light wavelengths in the flowering control of sugarcane. In this context, light-emitting diodes (LEDs) remain efficient sources of light. Therefore, the combined use of photoperiod regimes with different light wavelengths and optimization of such treatment combinations might help to control and induce flowering in sugarcane parental clones. In sugarcane, FLOWERING LOCUS T (ScFT) orthologues from ScFT1 to ScFT13 have been identified, and interestingly, ScFT3 has evidently been identified as a floral inducer in sugarcane. However, independent assessments of different FT-like gene family members are recommended to comprehensively understand their role in the regulation of flowering. Similarly, we believe this review provides substantial information that is vital for the manipulation of flowering and exploitation of germplasm resources in sugarcane breeding.

GIGANTEA accelerates wheat heading time through gene interactions converging on FLOWERING LOCUS T1

Precise regulation of flowering time is critical for cereal crops to synchronize reproductive development with optimum environmental conditions, thereby maximizing grain yield. The plant-specific gene GIGANTEA (GI) plays an important role in the control of flowering time, with additional functions on the circadian clock and plant stress responses. In this study, we show that GI loss-of-function mutants in a photoperiod-sensitive tetraploid wheat background exhibit significant delays in heading time under both long-day (LD) and short-day photoperiods, with stronger effects under LD. However, this interaction between GI and photoperiod is no longer observed in isogenic lines carrying either a photoperiod-insensitive allele in the PHOTOPERIOD1 (PPD1) gene or a loss-of-function allele in EARLY FLOWERING 3 (ELF3), a known repressor of PPD1. These results suggest that the normal circadian regulation of PPD1 is required for the differential effect of GI on heading time in different photoperiods. Using crosses between mutant or transgenic plants of GI and those of critical genes in the flowering regulation pathway, we show that GI accelerates wheat heading time by promoting FLOWERING LOCUS T1 (FT1) expression via interactions with ELF3, VERNALIZATION 2 (VRN2), CONSTANS (CO), and the age-dependent microRNA172-APETALA2 (AP2) pathway, at both transcriptional and protein levels. Our study reveals conserved GI mechanisms between wheat and Arabidopsis but also identifies specific interactions of GI with the distinctive photoperiod and vernalization pathways of the temperate grasses. These results provide valuable knowledge for modulating wheat heading time and engineering new varieties better adapted to a changing environment.

Integrated transcriptome and metabolome analysis reveals anthocyanin biosynthesis mechanisms in pepper (Capsicum annuum L.) leaves under continuous blue light irradiation

BACKGROUND

Different metabolic compounds give pepper leaves and fruits their diverse colors. Anthocyanin accumulation is the main cause of the purple color of pepper leaves. The light environment is a critical factor affecting anthocyanin biosynthesis. It is essential that we understand how to use light to regulate anthocyanin biosynthesis in plants.

RESULT

Pepper leaves were significantly blue-purple only in continuous blue light or white light (with a blue light component) irradiation treatments, and the anthocyanin content of pepper leaves increased significantly after continuous blue light irradiation. This green-to-purple phenotype change in pepper leaves was due to the expression of different genes. We found that the anthocyanin synthesis precursor-related genes PAL and 4CL, as well as the structural genes F3H, DFR, ANS, BZ1, and F3'5'H in the anthocyanin synthesis pathway, had high expression under continuous blue light irradiation. Similarly, the expression of transcription factors MYB1R1-like, MYB48, MYB4-like isoform X1, bHLH143-like, and bHLH92-like isoform X3, and circadian rhythm-related genes LHY and COP1, were significantly increased after continuous blue light irradiation. A correlation network analysis revealed that these transcription factors and circadian rhythm-related genes were positively correlated with structural genes in the anthocyanin synthesis pathway. Metabolomic analysis showed that delphinidin-3-O-glucoside and delphinidin-3-O-rutinoside were significantly higher under continuous blue light irradiation relative to other light treatments. We selected 12 genes involved in anthocyanin synthesis in pepper leaves for qRT-PCR analysis, and the accuracy of the RNA-seq results was confirmed.

CONCLUSIONS

In this study, we found that blue light and 24-hour irradiation together induced the expression of key genes and the accumulation of metabolites in the anthocyanin synthesis pathway, thus promoting anthocyanin biosynthesis in pepper leaves. These results provide a basis for future study of the mechanisms of light quality and photoperiod in anthocyanin synthesis and metabolism, and our study may serve as a valuable reference for screening light ratios that regulate anthocyanin biosynthesis in plants.

The Function, Regulation, and Mechanism of Protein Turnover in Circadian Systems in Neurospora and Other Species

Circadian clocks drive a large array of physiological and behavioral activities. At the molecular level, circadian clocks are composed of positive and negative elements that form core oscillators generating the basic circadian rhythms. Over the course of the circadian period, circadian negative proteins undergo progressive hyperphosphorylation and eventually degrade, and their stability is finely controlled by complex post-translational pathways, including protein modifications, genetic codon preference, protein-protein interactions, chaperon-dependent conformation maintenance, degradation, etc. The effects of phosphorylation on the stability of circadian clock proteins are crucial for precisely determining protein function and turnover, and it has been proposed that the phosphorylation of core circadian clock proteins is tightly correlated with the circadian period. Nonetheless, recent studies have challenged this view. In this review, we summarize the research progress regarding the function, regulation, and mechanism of protein stability in the circadian clock systems of multiple model organisms, with an emphasis on Neurospora crassa, in which circadian mechanisms have been extensively investigated. Elucidation of the highly complex and dynamic regulation of protein stability in circadian clock networks would greatly benefit the integrated understanding of the function, regulation, and mechanism of protein stability in a wide spectrum of other biological processes.

Arabidopsis COP1 guides stomatal response in guard cells through pH regulation

Plants rely on precise regulation of their stomatal pores to effectively carry out photosynthesis while managing water status. The Arabidopsis CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), a critical light signaling repressor, is known to repress stomatal opening, but the exact cellular mechanisms remain unknown. Here, we show that COP1 regulates stomatal movement by controlling the pH levels in guard cells. cop1-4 mutants have larger stomatal apertures and disrupted pH dynamics within guard cells, characterized by increased vacuolar and cytosolic pH and reduced apoplastic pH, leading to abnormal stomatal responses. The altered pH profiles are attributed to the increased plasma membrane (PM) H+-ATPase activity of cop1-4 mutants. Moreover, cop1-4 mutants resist to growth defect caused by alkali stress posed on roots. Overall, our study highlights the crucial role of COP1 in maintaining pH homeostasis of guard cells by regulating PM H+-ATPase activity, and demonstrates how proton movement affects stomatal movement and plant growth.

GIGANTEA Unveiled: Exploring Its Diverse Roles and Mechanisms

GIGANTEA (GI) is a conserved nuclear protein crucial for orchestrating the clock-associated feedback loop in the circadian system by integrating light input, modulating gating mechanisms, and regulating circadian clock resetting. It serves as a core component which transmits blue light signals for circadian rhythm resetting and overseeing floral initiation. Beyond circadian functions, GI influences various aspects of plant development (chlorophyll accumulation, hypocotyl elongation, stomatal opening, and anthocyanin metabolism). GI has also been implicated to play a pivotal role in response to stresses such as freezing, thermomorphogenic stresses, salinity, drought, and osmotic stresses. Positioned at the hub of complex genetic networks, GI interacts with hormonal signaling pathways like abscisic acid (ABA), gibberellin (GA), salicylic acid (SA), and brassinosteroids (BRs) at multiple regulatory levels. This intricate interplay enables GI to balance stress responses, promoting growth and flowering, and optimize plant productivity. This review delves into the multifaceted roles of GI, supported by genetic and molecular evidence, and recent insights into the dynamic interplay between flowering and stress responses, which enhance plants' adaptability to environmental challenges.

Mathematical Modeling of Photo- and Thermomorphogenesis in Plants

Increased day lengths and warm conditions inversely affect plant growth by directly modulating nuclear phyB, ELF3, and COP1 levels. Quantitative measures of the hypocotyl length have been key to gaining a deeper understanding of this complex regulatory network, while similar quantitative data are the foundation for many studies in plant biology. Here, we explore the application of mathematical modeling, specifically ordinary differential equations (ODEs), to understand plant responses to these environmental cues. We provide a comprehensive guide to constructing, simulating, and fitting these models to data, using the law of mass action to study the evolution of molecular species. The fundamental principles of these models are introduced, highlighting their utility in deciphering complex plant physiological interactions and testing hypotheses. This brief introduction will not allow experimentalists without a mathematical background to run their own simulations overnight, but it will help them grasp modeling principles and communicate with more theory-inclined colleagues.

Environmental F actors coordinate circadian clock function and rhythm to regulate plant development

Changes in the external environment necessitate plant growth plasticity, with environmental signals such as light, temperature, and humidity regulating growth and development. The plant circadian clock is a biological time keeper that can be "reset" to adjust internal time to changes in the external environment. Exploring the regulatory mechanisms behind plant acclimation to environmental factors is important for understanding how plant growth and development are shaped and for boosting agricultural production. In this review, we summarize recent insights into the coordinated regulation of plant growth and development by environmental signals and the circadian clock, further discussing the potential of this knowledge.

The Roles of the PSEUDO-RESPONSE REGULATORs in Circadian Clock and Flowering Time in Medicago truncatula

PSEUDO-RESPONSE REGULATORs (PRRs) play key roles in the circadian rhythms and flowering in plants. Here, we identified the four members of the PRR family in Medicago truncatula, including MtPRR9a, MtPRR9b, MtPRR7 and MtPRR5, and isolated their Tnt1 retrotransposon-tagged mutants. They were expressed in different organs and were nuclear-localized. The four MtPRRs genes played important roles in normal clock rhythmicity maintenance by negatively regulating the expression of MtGI and MtLHY. Surprisingly, the four MtPRRs functioned redundantly in regulating flowering time under long-day conditions, and the quadruple mutant flowered earlier. Moreover, MtPRR can recruit the MtTPL/MtTPR corepressors and the other MtPRRs to form heterodimers to constitute the core mechanism of the circadian oscillator.

Involvement of CONSTANS-like Proteins in Plant Flowering and Abiotic Stress Response

The process of flowering in plants is a pivotal stage in their life cycle, and the CONSTANS-like (COL) protein family, known for its photoperiod sensing ability, plays a crucial role in regulating plant flowering. Over the past two decades, homologous genes of COL have been identified in various plant species, leading to significant advancements in comprehending their involvement in the flowering pathway and response to abiotic stress. This article presents novel research progress on the structural aspects of COL proteins and their regulatory patterns within transcription complexes. Additionally, we reviewed recent information about their participation in flowering and abiotic stress response, aiming to provide a more comprehensive understanding of the functions of COL proteins.

CONSTANS interacts with and antagonizes ABF transcription factors during salt stress under long-day conditions

CONSTANS (CO) is a critical regulator of flowering that combines photoperiodic and circadian signals in Arabidopsis (Arabidopsis thaliana). CO is expressed in multiple tissues, including seedling roots and young leaves. However, the roles and underlying mechanisms of CO in modulating physiological processes outside of flowering remain obscure. Here, we show that the expression of CO responds to salinity treatment. CO negatively mediated salinity tolerance under long-day (LD) conditions. Seedlings from co-mutants were more tolerant to salinity stress, whereas overexpression of CO resulted in plants with reduced tolerance to salinity stress. Further genetic analyses revealed the negative involvement of GIGANTEA (GI) in salinity tolerance requires a functional CO. Mechanistic analysis demonstrated that CO physically interacts with 4 critical basic leucine zipper (bZIP) transcription factors; ABSCISIC ACID-RESPONSIVE ELEMENT BINDING FACTOR1 (ABF1), ABF2, ABF3, and ABF4. Disrupting these ABFs made plants hypersensitive to salinity stress, demonstrating that ABFs enhance salinity tolerance. Moreover, ABF mutations largely rescued the salinity-tolerant phenotype of co-mutants. CO suppresses the expression of several salinity-responsive genes and influences the transcriptional regulation function of ABF3. Collectively, our results show that the LD-induced CO works antagonistically with ABFs to modulate salinity responses, thus revealing how CO negatively regulates plant adaptation to salinity stress.

Characterizing the circadian connectome of Ocimum tenuiflorum using an integrated network theoretic framework

Across the three domains of life, circadian clock is known to regulate vital physiological processes, like, growth, development, defence etc. by anticipating environmental cues. In this work, we report an integrated network theoretic methodology comprising of random walk with restart and graphlet degree vectors to characterize genome wide core circadian clock and clock associated raw candidate proteins in a plant for which protein interaction information is available. As a case study, we have implemented this framework in Ocimum tenuiflorum (Tulsi); one of the most valuable medicinal plants that has been utilized since ancient times in the management of a large number of diseases. For that, 24 core clock (CC) proteins were mined in 56 template plant genomes to build their hidden Markov models (HMMs). These HMMs were then used to identify 24 core clock proteins in O. tenuiflorum. The local topology of the interologous Tulsi protein interaction network was explored to predict the CC associated raw candidate proteins. Statistical and biological significance of the raw candidates was determined using permutation and enrichment tests. A total of 66 putative CC associated proteins were identified and their functional annotation was performed.

Light and temperature perceptions go through a phase separation

Light and temperature are two distinct but closely linked environmental factors that profoundly affect plant growth and development. Biomolecular condensates are membraneless micron-scale compartments formed through liquid-liquid phase separation, which have been shown to be involved in a wide range of biological processes. In the last few years, biomolecular condensates are emerged to serve as phase separation-based sensors for plant sensing and/or responding to external environmental cues. This review summarizes the recently reported plant biomolecular condensates in sensing light and temperature signals. The current understanding of the biophysical properties and the action modes of phase separation-based environmental sensors are highlighted. Unresolved questions and possible challenges for future studies of phase-separation sensors are also discussed.

HSP90 in morphogenesis: taking the heat and keeping the dark

This article is a Commentary on Zeng et al. (2023), 239: 1253–1265.

The mechanisms of optimal nitrogen conditions to accelerate flowering of Chrysanthemum vestitum under short day based on transcriptome analysis

Nitrogen (N) plays an important role in the development of plants, with N application having been shown to accelerate flowering of cultivated plants. However, the mechanism of optimal N conditions to accelerate flowering of short-day plants is still unclear. In this study, it was found that Chrysanthemum vestitum is a typical short-day plant like most chrysanthemum varieties, and its flowering must go through a short-day induction stage. Further observations on the growth of C. vestitum showed that the N range of external application for growth was limited to between 0.25 and 2.50 mM. The results showed that, under optimal N (ON, 1.25 mM) conditions, the plants increased rapidly and flowering time was advanced; under high N (HN, 2.50 mM) or limited N (LN, 0.25 mM) conditions, the growth of plants were inhibited and flowering time was delayed. On the basis of transcriptome data, analysis of differentially expressed genes (DEGs) revealed that the floral-related genes B-box19 (BBX19), Cryptochromes (CRYs), CONSTANS-like (COLs), nitrate transporter protein (NRT), and NIN-like protein (NLP) could respond to N availability. Most of the genes in the photoperiod pathway were upregulated by ON conditions, and their expression was inhibited under HN and LN conditions. Our findings indicated that N could affect flowering by regulating the transcription levels of genes that are involved mainly in the photoperiod pathway. These candidate genes provide important clues for the subsequent analysis of the mechanism of N-induced flowering of short-day plants, and provide a possibility to improve the flowering of chrysanthemum by molecular breeding.

Photoperiodic flowering in Arabidopsis: Multilayered regulatory mechanisms of CONSTANS and the florigen FLOWERING LOCUS T

The timing of flowering affects the success of sexual reproduction. This developmental event also determines crop yield, biomass, and longevity. Therefore, this mechanism has been targeted for improvement along with crop domestication. The underlying mechanisms of flowering are highly conserved in angiosperms. Central to these mechanisms is how environmental and endogenous conditions control transcriptional regulation of the FLOWERING LOCUS T (FT) gene, which initiates floral development under long-day conditions in Arabidopsis. Since the identification of FT as florigen, efforts have been made to understand the regulatory mechanisms of FT expression. Although many transcriptional regulators have been shown to directly influence FT, the question of how they coordinately control the spatiotemporal expression patterns of FT still requires further investigation. Among FT regulators, CONSTANS (CO) is the primary one whose protein stability is tightly controlled by phosphorylation and ubiquitination/proteasome-mediated mechanisms. In addition, various CO interaction partners, some of them previously identified as FT transcriptional regulators, positively or negatively modulate CO protein activity. The FT promoter possesses several transcriptional regulatory "blocks," highly conserved regions among Brassicaceae plants. Different transcription factors bind to specific blocks and affect FT expression, often causing topological changes in FT chromatin structure, such as the formation of DNA loops. We discuss the current understanding of the regulation of FT expression mainly in Arabidopsis and propose future directions related to this topic.

The Regulatory Networks of the Circadian Clock Involved in Plant Adaptation and Crop Yield

Global climatic change increasingly threatens plant adaptation and crop yields. By synchronizing internal biological processes, including photosynthesis, metabolism, and responses to biotic and abiotic stress, with external environmental cures, such as light and temperature, the circadian clock benefits plant adaptation and crop yield. In this review, we focus on the multiple levels of interaction between the plant circadian clock and environmental factors, and we summarize recent progresses on how the circadian clock affects yield. In addition, we propose potential strategies for better utilizing the current knowledge of circadian biology in crop production in the future.

EARLY FLOWERING 3 interactions with PHYTOCHROME B and PHOTOPERIOD1 are critical for the photoperiodic regulation of wheat heading time

The photoperiodic response is critical for plants to adjust their reproductive phase to the most favorable season. Wheat heads earlier under long days (LD) than under short days (SD) and this difference is mainly regulated by the PHOTOPERIOD1 (PPD1) gene. Tetraploid wheat plants carrying the Ppd-A1a allele with a large deletion in the promoter head earlier under SD than plants carrying the wildtype Ppd-A1b allele with an intact promoter. Phytochromes PHYB and PHYC are necessary for the light activation of PPD1, and mutations in either of these genes result in the downregulation of PPD1 and very late heading time. We show here that both effects are reverted when the phyB mutant is combined with loss-of-function mutations in EARLY FLOWERING 3 (ELF3), a component of the Evening Complex (EC) in the circadian clock. We also show that the wheat ELF3 protein interacts with PHYB and PHYC, is rapidly modified by light, and binds to the PPD1 promoter in planta (likely as part of the EC). Deletion of the ELF3 binding region in the Ppd-A1a promoter results in PPD1 upregulation at dawn, similar to PPD1 alleles with intact promoters in the elf3 mutant background. The upregulation of PPD1 is correlated with the upregulation of the florigen gene FLOWERING LOCUS T1 (FT1) and early heading time. Loss-of-function mutations in PPD1 result in the downregulation of FT1 and delayed heading, even when combined with the elf3 mutation. Taken together, these results indicate that ELF3 operates downstream of PHYB as a direct transcriptional repressor of PPD1, and that this repression is relaxed both by light and by the deletion of the ELF3 binding region in the Ppd-A1a promoter. In summary, the regulation of the light mediated activation of PPD1 by ELF3 is critical for the photoperiodic regulation of wheat heading time.

Novel exotic alleles of EARLY FLOWERING 3 determine plant development in barley

EARLY FLOWERING 3 (ELF3) is an important regulator of various physiological and developmental processes and hence may serve to improve plant adaptation which will be substantial for future plant breeding. To expand the limited knowledge on barley ELF3 in determining agronomic traits, we conducted field studies with heterogeneous inbred families (HIFs) derived from selected lines of the wild barley nested association mapping population HEB-25. During two growing seasons, phenotypes of nearly isogenic HIF sister lines, segregating for exotic and cultivated alleles at the ELF3 locus, were compared for ten developmental and yield-related traits. We determine novel exotic ELF3 alleles and show that HIF lines, carrying the exotic ELF3 allele, accelerated plant development compared to the cultivated ELF3 allele, depending on the genetic background. Remarkably, the most extreme effects on phenology could be attributed to one exotic ELF3 allele differing from the cultivated Barke ELF3 allele in only one SNP. This SNP causes an amino acid substitution (W669G), which predictively has an impact on the protein structure of ELF3, thereby possibly affecting phase separation behaviour and nano-compartment formation of ELF3 and, potentially, also affecting its local cellular interactions causing significant trait differences between HIF sister lines.

Phytochrome B photobodies are comprised of phytochrome B and its primary and secondary interacting proteins

Phytochrome B (phyB) is a plant photoreceptor that forms a membraneless organelle called a photobody. However, its constituents are not fully known. Here, we isolated phyB photobodies from Arabidopsis leaves using fluorescence-activated particle sorting and analyzed their components. We found that a photobody comprises ~1,500 phyB dimers along with other proteins that could be classified into two groups: The first includes proteins that directly interact with phyB and localize to the photobody when expressed in protoplasts, while the second includes proteins that interact with the first group proteins and require co-expression of a first-group protein to localize to the photobody. As an example of the second group, TOPLESS interacts with PHOTOPERIODIC CONTROL OF HYPOCOTYL 1 (PCH1) and localizes to the photobody when co-expressed with PCH1. Together, our results support that phyB photobodies include not only phyB and its primary interacting proteins but also its secondary interacting proteins.

GIGANTEA supresses wilt disease resistance by down-regulating the jasmonate signaling in Arabidopsis thaliana

GIGANTEA (GI) is a plant-specific nuclear protein that plays a pleiotropic role in the growth and development of plants. GI's involvement in circadian clock function, flowering time regulation, and various types of abiotic stress tolerance has been well documented in recent years. Here, the role of GI in response to Fusarium oxysporum (F. oxysporum) infection is investigated at the molecular level comparing Col-0 WT with the gi-100 mutant in Arabidopsis thaliana. Disease progression, photosynthetic parameters, and comparative anatomy confirmed that the spread and damage caused by pathogen infection were less severe in gi-100 than in Col-0 WT plants. F. oxysporum infection induces a remarkable accumulation of GI protein. Our report showed that it is not involved in flowering time regulation during F. oxysporum infection. Estimation of defense hormone after infection showed that jasmonic acid (JA) level is higher and salicylic acid (SA) level is lower in gi-100 compared to Col-0 WT. Here, we show that the relative transcript expression of CORONATINE INSENSITIVE1 (COI1) and PLANT DEFENSIN1.2 (PDF1.2) as a marker of the JA pathway is significantly higher while ISOCHORISMATE SYNTHASE1 (ICS1) and NON-EXPRESSOR OF PATHOGENESIS-RELATED GENES1 (NPR1), the markers of the SA pathway, are downregulated in the gi-100 mutants compared to Col-0 plants. The present study convincingly suggests that the GI module promotes susceptibility to F. oxysporum infection by inducing the SA pathway and inhibiting JA signaling in A. thaliana.

HOS15 represses flowering by promoting GIGANTEA degradation in response to low temperature in Arabidopsis

Flowering is the primary stage of the plant developmental transition and is tightly regulated by environmental factors such as light and temperature. However, the mechanisms by which temperature signals are integrated into the photoperiodic flowering pathway are still poorly understood. Here, we demonstrate that HOS15, which is known as a GI transcriptional repressor in the photoperiodic flowering pathway, controls flowering time in response to low ambient temperature. At 16°C, the hos15 mutant exhibits an early flowering phenotype, and HOS15 acts upstream of photoperiodic flowering genes (GI, CO, and FT). GI protein abundance is increased in the hos15 mutant and is insensitive to the proteasome inhibitor MG132. Furthermore, the hos15 mutant has a defect in low ambient temperature-mediated GI degradation, and HOS15 interacts with COP1, an E3 ubiquitin ligase for GI degradation. Phenotypic analyses of the hos15 cop1 double mutant revealed that repression of flowering by HOS15 is dependent on COP1 at 16°C. However, the HOS15-COP1 interaction was attenuated at 16°C, and GI protein abundance was additively increased in the hos15 cop1 double mutant, indicating that HOS15 acts independently of COP1 in GI turnover at low ambient temperature. This study proposes that HOS15 controls GI abundance through multiple modes as an E3 ubiquitin ligase and transcriptional repressor to coordinate appropriate flowering time in response to ambient environmental conditions such as temperature and day length.

Photoperiod Genes Contribute to Daylength-Sensing and Breeding in Rice

Rice (Oryza sativa L.), one of the most important food crops worldwide, is a facultative short-day (SD) plant in which flowering is modulated by seasonal and temperature cues. The photoperiodic molecular network is the core network for regulating flowering in rice, and is composed of photoreceptors, a circadian clock, a photoperiodic flowering core module, and florigen genes. The Hd1-DTH8-Ghd7-PRR37 module, a photoperiodic flowering core module, improves the latitude adaptation through mediating the multiple daylength-sensing processes in rice. However, how the other photoperiod-related genes regulate daylength-sensing and latitude adaptation remains largely unknown. Here, we determined that mutations in the photoreceptor and circadian clock genes can generate different daylength-sensing processes. Furthermore, we measured the yield-related traits in various mutants, including the main panicle length, grains per panicle, seed-setting rate, hundred-grain weight, and yield per panicle. Our results showed that the prr37, elf3-1 and ehd1 mutants can change the daylength-sensing processes and exhibit longer main panicle lengths and more grains per panicle. Hence, the PRR37, ELF3-1 and Ehd1 locus has excellent potential for latitude adaptation and production improvement in rice breeding. In summary, this study systematically explored how vital elements of the photoperiod network regulate daylength sensing and yield traits, providing critical information for their breeding applications.

Recent advances and future perspectives in early-maturing cotton research

Cotton's fundamental requirements for long periods of growth and specific seasonal temperatures limit the global arable areas that can be utilized to cultivate cotton. This constraint can be alleviated by breeding for early-maturing varieties. By delaying the sowing dates without impacting the boll-opening time, early-maturing varieties not only mitigate the yield losses brought on by unfavorable weathers in early spring and late autumn but also help reducing the competition between cotton and other crops for arable land, thereby optimizing the cropping system. This review presents studies and breeding efforts for early-maturing cotton, which efficiently pyramid early maturity, high-quality, multiresistance traits, and suitable plant architecture by leveraging pleiotropic genes. Attempts are also made to summarize our current understanding of the molecular mechanisms underlying early maturation, which involves many pathways such as epigenetic, circadian clock, and hormone signaling pathways. Moreover, new avenues and effective measures are proposed for fine-scale breeding of early-maturing crops to ensure the healthy development of the agricultural industry.

HSP90s are required for hypocotyl elongation during skotomorphogenesis and thermomorphogenesis via the COP1-ELF3-PIF4 pathway in Arabidopsis

Light and temperature are two key environmental signals that share several molecular components that, in turn, regulate plant growth. Darkness and high ambient temperatures promote skoto- and thermomorphogenesis, including stem elongation. Heat shock proteins 90 (HSP90s) facilitate the adaptation of organisms to various adverse environmental stimuli. Here, we showed that HSP90s are required for hypocotyl elongation during both skoto- and thermomorphogenesis. When HSP90s activities are impaired by the knockdown of HSP90s expression or the application of HSP90 inhibitors, the expression levels and protein abundance of PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) markedly decreased. EARLY FLOWERING 3 (ELF3) deficiency was resistant to the inhibition of HSP90s activities. Furthermore, HSP90s interacted with and destabilized ELF3. In the CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) mutant, the changes in endogenous PIF4 and ELF3 protein levels caused by the inhibition of HSP90s activities were abolished. HSP90s enhanced the interaction between COP1 and ELF3, reduced ELF3 functional effects on PIF4 and modulated hypocotyl elongation during skoto- and thermomorphogenesis. Our results indicated that HSP90s participate in light and temperature signalling via the COP1-ELF3-PIF4 module to regulate hypocotyl growth in changing environments.