Co-incidence of Damage and Microbial Patterns Controls Localized Immune Responses in Roots.

Recognition of microbe-associated molecular patterns (MAMPs) is crucial for the plant's immune response. How this sophisticated perception system can be usefully deployed in roots, continuously exposed to microbes, remains a mystery. By analyzing MAMP receptor expression and response at cellular resolution in Arabidopsis, we observed that differentiated outer cell layers show low expression of pattern-recognition receptors (PRRs) and lack MAMP responsiveness. Yet, these cells can be gated to become responsive by neighbor cell damage. Laser ablation of small cell clusters strongly upregulates PRR expression in their vicinity, and elevated receptor expression is sufficient to induce responsiveness in non-responsive cells. Finally, localized damage also leads to immune responses to otherwise non-immunogenic, beneficial bacteria. Damage-gating is overridden by receptor overexpression, which antagonizes colonization. Our findings that cellular damage can "switch on" local immune responses helps to conceptualize how MAMP perception can be used despite the presence of microbial patterns in the soil.

Probing plant signal processing optogenetically by two channelrhodopsins.

Early plant responses to different stress situations often encompass cytosolic Ca2+ increases, plasma membrane depolarization and the generation of reactive oxygen species1-3. However, the mechanisms by which these signalling elements are translated into defined physiological outcomes are poorly understood. Here, to study the basis for encoding of specificity in plant signal processing, we used light-gated ion channels (channelrhodopsins). We developed a genetically engineered channelrhodopsin variant called XXM 2.0 with high Ca2+ conductance that enabled triggering cytosolic Ca2+ elevations in planta. Plant responses to light-induced Ca2+ influx through XXM 2.0 were studied side by side with effects caused by an anion efflux through the light-gated anion channelrhodopsin ACR1 2.04. Although both tools triggered membrane depolarizations, their activation led to distinct plant stress responses: XXM 2.0-induced Ca2+ signals stimulated production of reactive oxygen species and defence mechanisms; ACR1 2.0-mediated anion efflux triggered drought stress responses. Our findings imply that discrete Ca2+ signals and anion efflux serve as triggers for specific metabolic and transcriptional reprogramming enabling plants to adapt to particular stress situations. Our optogenetics approach unveiled that within plant leaves, distinct physiological responses are triggered by specific ion fluxes, which are accompanied by similar electrical signals.

Light Regulates Plant Alternative Splicing through the Control of Transcriptional Elongation.

Light makes carbon fixation possible, allowing plant and animal life on Earth. We have previously shown that light regulates alternative splicing in plants. Light initiates a chloroplast retrograde signaling that regulates nuclear alternative splicing of a subset of Arabidopsis thaliana transcripts. Here, we show that light promotes RNA polymerase II (Pol II) elongation in the affected genes, whereas in darkness, elongation is lower. These changes in transcription are consistent with elongation causing the observed changes in alternative splicing, as revealed by different drug treatments and genetic evidence. The light control of splicing and elongation is abolished in an Arabidopsis mutant defective in the transcription factor IIS (TFIIS). We report that the chloroplast control of nuclear alternative splicing in plants responds to the kinetic coupling mechanism found in mammalian cells, providing unique evidence that coupling is important for a whole organism to respond to environmental cues.

Shade-induced ROS/NO reinforce COP1-mediated diffuse cell growth.

Canopy shade enhances the activity of PHYTOCHROME INTERACTING FACTORs (PIFs) to boost auxin synthesis in the cotyledons. Auxin, together with local PIFs and their positive regulator CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1), promotes hypocotyl growth to facilitate access to light. Whether shade alters the cellular redox status thereby affecting growth responses, remains unexplored. Here, we show that, under shade, high auxin levels increased reactive oxygen species and nitric oxide accumulation in the hypocotyl of Arabidopsis. This nitroxidative environment favored the promotion of hypocotyl growth by COP1 under shade. We demonstrate that COP1 is S-nitrosylated, particularly under shade. Impairing this redox regulation enhanced COP1 degradation by the proteasome and diminished the capacity of COP1 to interact with target proteins and to promote hypocotyl growth. Disabling this regulation also generated transversal asymmetries in hypocotyl growth, indicating poor coordination among different cells, which resulted in random hypocotyl bending and predictably low ability to compete with neighbors. These findings highlight the significance of redox signaling in the control of diffuse growth during shade avoidance.

Detection and characterization of genome-wide mutations in M1 vegetative cells of gamma-irradiated Arabidopsis.

Radiation-induced mutations have been detected by whole-genome sequencing analyses of self-pollinated generations of mutagenized plants. However, large DNA alterations and mutations in non-germline cells were likely missed. In this study, in order to detect various types of mutations in mutagenized M1 plants, anthocyanin pigmentation was used as a visible marker of mutations. Arabidopsis seeds heterozygous for the anthocyanin biosynthetic genes were irradiated with gamma-rays. Anthocyanin-less vegetative sectors resulting from a loss of heterozygosity were isolated from the gamma-irradiated M1 plants. The whole-genome sequencing analysis of the sectors detected various mutations, including structural variations (SVs) and large deletions (≥100 bp), both of which have been less characterized in the previous researches using gamma-irradiated plant genomes of M2 or later generations. Various types of rejoined sites were found in SVs, including no-insertion/deletion (indel) sites, only-deletion sites, only-insertion sites, and indel sites, but the rejoined sites with 0-5 bp indels represented most of the SVs. Examinations of the junctions of rearrangements (SVs and large deletions), medium deletions (10-99 bp), and small deletions (2-9 bp) revealed unique features (i.e., frequency of insertions and microhomology) at the rejoined sites. These results suggest that they were formed preferentially via different processes. Additionally, mutations that occurred in putative single M1 cells were identified according to the distribution of their allele frequency. The estimated mutation frequencies and spectra of the M1 cells were similar to those of previously analyzed M2 cells, with the exception of the greater proportion of rearrangements in the M1 cells. These findings suggest there are no major differences in the small mutations (<100 bp) between vegetative and germline cells. Thus, this study generated valuable information that may help clarify the nature of gamma-irradiation-induced mutations and their occurrence in cells that develop into vegetative or reproductive tissues.

Low-dose 60Co-γ-ray irradiation promotes the growth of cucumber seedlings by inducing CsSAUR37 expression.

Cucumber (Cucumis sativus L.) is a major vegetable crop grown globally, with a cultivation history of more than 3000 years. The limited genetic diversity, low rate of intraspecific variation, and extended periods of traditional breeding have resulted in slow progress in their genetic research and the development of new varieties. Gamma (γ)-ray irradiation potentially accelerates the breeding progress; however, the biological and molecular effects of γ-ray irradiation on cucumbers are unknown. Exposing cucumber seeds to 0, 50, 100, 150, 200, and 250 Gy doses of 60Co-γ-ray irradiation, this study aimed to investigate the resulting phenotype and physiological characteristics of seedling treatment to determine the optimal irradiation dose. The results showed that low irradiation doses (50-100 Gy) enhanced root growth, hypocotyl elongation, and lateral root numbers, promoting seedling growth. However, high irradiation doses (150-250 Gy) significantly inhibited seed germination and growth, decreasing the survival rate of seedlings. More than 100 Gy irradiation significantly decreased the total chlorophyll content while increasing the malondialdehyde (MDA) and H2O2 content in cucumber. Transcriptome sequencing analysis at 0, 50, 100, 150, 200, and 250 Gy doses showed that gene expression significantly differed between low and high irradiation doses. Gene Ontology enrichment and functional pathway enrichment analyses revealed that the auxin response pathway played a crucial role in seedling growth under low irradiation doses. Further, gene function analysis revealed that small auxin up-regulated gene CsSAUR37 was a key gene that was overexpressed in response to low irradiation doses, promoting primary root elongation and enhancing lateral root numbers by regulating the expression of protein phosphatase 2Cs (PP2Cs) and auxin synthesis genes.

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.

Supplementing with monochromatic blue LED light during the day, rather than at night, increases anthocyanins in the berry skin of grapevine (Vitis vinifera L.).

MAIN CONCLUSION: Supplying monochromatic blue LED light during the day, but not at night, promotes early coloration and improves anthocyanin accumulation in the skin of grape berries. Specific light spectra, such as blue light, are known to promote the biosynthesis and accumulation of anthocyanins in fruit skins. However, research is scarce on whether supplement of blue light during different periods of one day can differ in their effect. Here, we compared the consequences of supplying blue light during the day and night on the accumulation of anthocyanins in pigmented grapevine (Vitis vinifera) berries. Two treatments of supplemented monochromatic blue light were tested, with light emitting diodes (LED) disposed close to the fruit zone, irradiating between 8:00 and 18:00 (Dayblue) or between 20:00 and 6:00 (Nightblue). Under the Dayblue treatment, berry coloration was accelerated and total anthocyanins in berry skins increased faster than the control (CK) and also when compared to the Nightblue condition. In fact, total anthocyanin content was similar between CK and Nightblue. qRT-PCR analysis indicated that Dayblue slightly improved the relative expression of the anthocyanin-structural gene UFGT and its regulator MYBA1. Instead, the expression of the light-reception and -signaling related genes CRY, HY5, HYH, and COP1 rapidly increased under Dayblue. This study provides insights into the effect of supplementing monochromatic LED blue light during the different periods of one day, on anthocyanins accumulation in the berry skin.

ScRNA-seq reveals dark- and light-induced differentially expressed gene atlases of seedling leaves in Arachis hypogaea L.

Although the regulatory mechanisms of dark and light-induced plant morphogenesis have been broadly investigated, the biological process in peanuts has not been systematically explored on single-cell resolution. Herein, 10 cell clusters were characterized using scRNA-seq-identified marker genes, based on 13 409 and 11 296 single cells from 1-week-old peanut seedling leaves grown under dark and light conditions. 6104 genes and 50 transcription factors (TFs) displayed significant expression patterns in distinct cell clusters, which provided gene resources for profiling dark/light-induced candidate genes. Further pseudo-time trajectory and cell cycle evidence supported that dark repressed the cell division and perturbed normal cell cycle, especially the PORA abundances correlated with 11 TFs highly enriched in mesophyll to restrict the chlorophyllide synthesis. Additionally, light repressed the epidermis cell developmental trajectory extending by inhibiting the growth hormone pathway, and 21 TFs probably contributed to the different genes transcriptional dynamic. Eventually, peanut AHL17 was identified from the profile of differentially expressed TFs, which encoded protein located in the nucleus promoted leaf epidermal cell enlargement when ectopically overexpressed in Arabidopsis through the regulatory phytohormone pathway. Overall, our study presents the different gene atlases in peanut etiolated and green seedlings, providing novel biological insights to elucidate light-induced leaf cell development at the single-cell level.

Far-red light enrichment affects gene expression and architecture as well as growth and photosynthesis in rice.

Plants use light as a resource and signal. Photons within the 400-700 nm waveband are considered photosynthetically active. Far-red photons (FR, 700-800 nm) are used by plants to detect nearby vegetation and elicit the shade avoidance syndrome. In addition, FR photons have also been shown to contribute to photosynthesis, but knowledge about these dual effects remains scarce. Here, we study shoot-architectural and photosynthetic responses to supplemental FR light during the photoperiod in several rice varieties. We observed that FR enrichment only mildly affected the rice transcriptome and shoot architecture as compared to established model species, whereas leaf formation, tillering and biomass accumulation were clearly promoted. Consistent with this growth promotion, we found that CO2-fixation in supplemental FR was strongly enhanced, especially in plants acclimated to FR-enriched conditions as compared to control conditions. This growth promotion dominates the effects of FR photons on shoot development and architecture. When substituting FR enrichment with an end-of-day FR pulse, this prevented photosynthesis-promoting effects and elicited shade avoidance responses. We conclude that FR photons can have a dual role, where effects depend on the environmental context: in addition to being an environmental signal, they are also a potent source of harvestable energy.

Blue light-dependent interactions of CRY1 with GID1 and DELLA proteins regulate gibberellin signaling and photomorphogenesis in Arabidopsis.

Cryptochromes are blue light photoreceptors that mediate various light responses in plants and mammals. In Arabidopsis (Arabidopsis thaliana), cryptochrome 1 (CRY1) mediates blue light-induced photomorphogenesis, which is characterized by reduced hypocotyl elongation and enhanced anthocyanin production, whereas gibberellin (GA) signaling mediated by the GA receptor GA-INSENSITIVE DWARF1 (GID1) and DELLA proteins promotes hypocotyl elongation and inhibits anthocyanin accumulation. Whether CRY1 control of photomorphogenesis involves regulation of GA signaling is largely unknown. Here, we show that CRY1 signaling involves the inhibition of GA signaling through repression of GA-induced degradation of DELLA proteins. CRY1 physically interacts with DELLA proteins in a blue light-dependent manner, leading to their dissociation from SLEEPY1 (SLY1) and the inhibition of their ubiquitination. Moreover, CRY1 interacts directly with GID1 in a blue light-dependent but GA-independent manner, leading to the inhibition of the interaction between GID1 with DELLA proteins. These findings suggest that CRY1 controls photomorphogenesis through inhibition of GA-induced degradation of DELLA proteins and GA signaling, which is mediated by CRY1 inhibition of the interactions of DELLA proteins with GID1 and SCFSLY1, respectively.

The PIF1-miR408-PLANTACYANIN repression cascade regulates light-dependent seed germination.

Light-dependent seed germination is a vital process for many seed plants. A decisive event in light-induced germination is degradation of the central repressor PHYTOCHROME INTERACTING FACTOR 1 (PIF1). The balance between gibberellic acid (GA) and abscisic acid (ABA) helps to control germination. However, the cellular mechanisms linking PIF1 turnover to hormonal balancing remain elusive. Here, employing far-red light-induced Arabidopsis thaliana seed germination as the experimental system, we identified PLANTACYANIN (PCY) as an inhibitor of germination. It is a blue copper protein associated with the vacuole that is both highly expressed in mature seeds and rapidly silenced during germination. Molecular analyses showed that PIF1 binds to the miR408 promoter and represses miR408 accumulation. This in turn posttranscriptionally modulates PCY abundance, forming the PIF1-miR408-PCY repression cascade for translating PIF1 turnover to PCY turnover during early germination. Genetic analysis, RNA-sequencing, and hormone quantification revealed that PCY is necessary and sufficient to maintain the PIF1-mediated seed transcriptome and the low-GA-high-ABA state. Furthermore, we found that PCY domain organization and regulation by miR408 are conserved features in seed plants. These results revealed a cellular mechanism whereby PIF1-relayed external light signals are converted through PCY turnover to internal hormonal profiles for controlling seed germination.

Ultraviolet-induced melanisation in lichens: physiological traits and transcriptome profile.

Lichens are important components of high-latitude boreal and Arctic habitats. While stress tolerant, they are among the most sensitive ecosystem components to climate change, in particular, an increase in ultraviolet light (UV) arising from polar ozone depletion and deforestation. This study is the first to explore the effects of UV-B on gene expression in lichens to predict metabolic pathways involved in tolerance. Using transcriptome profiling and bioinformatic analyses, here we studied the effects of UV-B on gene expression in lichens using Lobaria pulmonaria (L.) Hoff. as a model species. UV-B exposure causes significant browning of the upper cortex of the thallus, which correlates to an increased expression of biosynthetic gene clusters involved in the synthesis of eu- and allomelanins and melanin precursors. Based on transcriptome analyses, we suggest that the biosynthesis of melanins and other secondary metabolites, such as naphthalene derivates, tropolones, anthraquinones, and xanthones, is a trade-off that lichens pay to protect essential metabolic processes such as photosynthesis and respiration. Expression profiles of general stress-associated genes, in particular, related to reactive oxygen species scavenging, protection of proteins, and DNA repair, clearly indicate that the mycobiont is the more UV-B-responsive and susceptible partner in lichen symbiosis. Our findings demonstrate that UV-B stress activates an intricate gene network involved in tolerance mechanisms of lichen symbionts. Knowledge obtained here may enable the prediction of likely effects on lichen biodiversity caused by climate change and pollution.

OsUVR8b, rather than OsUVR8a, plays a predominant role in rice UVR8-mediated UV-B response.

UV RESISTANCE LOCUS 8 (UVR8) has been identified in Arabidopsis thaliana as the receptor mediating responses to UV-B radiation. However, UVR8-mediated UV-B signaling pathways in rice, which possesses two proteins (UVR8a and UVR8b) with high identities to AtUVR8, remain largely unknown. Here, UVR8a/b were found to be predominantly expressed in rice leaves and leaf sheaths, while the levels of UVR8b transcript and UVR8b protein were both higher than those of UVR8a. Compared to wild-type (WT) plants, uvr8b and uvr8a uvr8b rice mutants exposed to UV-B showed reduced UV-B-induced growth inhibition and upregulation of CHS and HY5 transcripts alongside UV-B acclimation. However, uvr8a mutant was similar to WT plants and exhibited changes comparable with WT. Overexpressing OsUVR8a/b enhanced UV-B-induced growth inhibition and acclimation to UV-B. UV-B was able to enhance the interaction between E3 ubiquitin ligase OsCOP1 and OsUVR8a/b, whereas the interaction of the homologous protein of Arabidopsis REPRESSOR OF UV-B PHOTOMORPHOGENESIS2 (AtRUP2) in rice with OsUVR8a/b was independent of UV-B. Additionally, OsUVR8a/b proteins were also found in the nucleus and cytoplasm even in the absence of UV-B. The abundance of OsUVR8 monomer showed an invisible change in the leaves of rice seedlings transferred from white light to that supplemented with UV-B, even though UV-B was able to weaken the interactions between OsUVR8a and OsUVR8b homo and heterodimers. Therefore, both OsUVR8a and OsUVR8b, which have different localization and response patterns compared with AtUVR8, function in the response of rice to UV-B radiation, whereas OsUVR8b plays a predominant role in this process.

Evaluation of the roles of brassinosteroid, gibberellin and auxin for tomato internode elongation in response to low red:far-red light.

In this study, we explore the interplay between the plant hormones gibberellins (GA), brassinosteroids (BR), and Indole-3-Acetic Acid (IAA) in their collective impact on plant shade avoidance elongation under varying light conditions. We focus particularly on low Red:Far-red (R:FR) light conditions achieved by supplementing the background light with FR. We characterized the tomato internode response to low R:FR and, with RNA-seq analysis, we were able to identify some of the potential regulatory hormonal pathways. Through a series of exogenous pharmacological modulations of GA, IAA, and BR, we demonstrate that GA and BR are sufficient but also necessary for inducing stem elongation under low R:FR light conditions. Intriguingly, while IAA alone shows limited effects, its combination with GA yields significant elongation, suggesting a nuanced hormonal balance. Furthermore, we unveil the complex interplay of these hormones under light with low R:FR, where the suppression of one hormone's effect can be compensated by the others. This study provides insights into the hormonal mechanisms governing plant adaptation to light, highlighting the intricate and adaptable nature of plant growth responses. Our findings have far-reaching implications for agricultural practices, offering potential strategies for optimizing plant growth and productivity in various lighting environments.

Exploring the effects of red light night break on the defence mechanisms of tomato against fungal pathogen Botrytis cinerea.

Plant infections caused by fungi lead to significant crop losses worldwide every year. This study aims to better understand the plant defence mechanisms regulated by red light, in particular, the effects of red light at night when most phytopathogens are highly infectious. Our results showed that superoxide production significantly increased immediately after red light exposure and, together with hydrogen peroxide levels, was highest at dawn after 30 min of nocturnal red-light treatment. In parallel, red-light-induced expression and increased the activities of several antioxidant enzymes. The nocturnal red light did not affect salicylic acid but increased jasmonic acid levels immediately after illumination, whereas abscisic acid levels increased 3 h after nocturnal red-light exposure at dawn. Based on the RNAseq data, red light immediately increased the transcription of several chloroplastic chlorophyll a-b binding protein and circadian rhythm-related genes, such as Constans 1, CONSTANS interacting protein 1 and zinc finger protein CONSTANS-LIKE 10. In addition, the levels of several transcription factors were also increased after red light exposure, such as the DOF zinc finger protein and a MYB transcription factor involved in the regulation of circadian rhythms and defence responses in tomato. In addition to identifying these key transcription factors in tomato, the application of red light at night for one week not only reactivated key antioxidant enzymes at the gene and enzyme activity level at dawn but also contributed to a more efficient and successful defence against Botrytis cinerea infection.

Elucidating light and temperature-dependent signalling pathways from shoot to root in rice plants: Implications for stress responses.

The main aim of this work was to better understand how the low temperature signal from the leaves may affect the stress responses in the roots, and how the light conditions modify certain stress acclimation processes in rice plants. Rice plants grown at 27°C were exposed to low temperatures (12°C) with different light intensities, and in the case of some groups of plants, only the leaves received the cold, while the roots remained at control temperature. RNA sequencing focusing on the roots of plants grown under normal growth light conditions found 525 differentially expressed genes in different comparisons. Exposure to low temperature led to more down-regulated than up-regulated genes. Comparison between roots of the leaf-stressed plants and whole cold-treated or control plants revealed that nitrogen metabolism and nitric oxide-related signalling, as well as the phenylpropanoid-related processes, were specifically affected. Real-time PCR results focusing on the COLD1 and polyamine oxidase genes, as well as metabolomics targeting hormonal changes and phenolic compounds also showed that not only cold exposure of the leaves, either alone or together with the roots, but also the light conditions may influence certain stress responses in the roots of rice plants.

Calcium signaling regulates the accumulation of phenolic acids in response to UV-B stress in Rhododendron chrysanthum Pall.

KEY MESSAGE: This study, using multi-omics combined with physiologic assays, found that calcium-ion signaling can regulate phenolic acid accumulation in R. chrysanthum leaves in response to UV-B stress. UV-B stress is a severe abiotic stress capable of destroying cellular structures and affecting plant growth. Rhododendron chrysanthum Pall. (R. chrysanthum) is a plant that has been exposed to high levels of UV-B radiation for an extended period, leading to the development of adaptive responses to mitigate UV-B stress. As such, it serves as a valuable experimental material for studying plant resilience to UV-B stress. We utilized R. chrysanthum as the experimental material and subjected it to UV-B stress. We conducted a comprehensive analysis of the changes in R. chrysanthum under both control and UV-B stress conditions using multi-omic and physiologic assays. Our aim was to investigate the molecular mechanism underlying R. chrysanthum's resistance to UV-B stress, with a focus on calcium-ion signaling. UV-B stress was found to impact the photosynthesis of R. chrysanthum by decreasing the maximum photosynthetic efficiency of photosystem II, reducing Fm, and increasing F0. In addition, the composition of numerous phenolic acid compounds was significantly altered. Genes and proteins related to calcium signaling showed significant differences, with some proteins (CML, CPK1, CRK3, ATP2C, ERG3, CAR7) being modified by acetylation. The correlation between genes and proteins involved in calcium signaling and phenolic compounds suggested that calcium signaling may play a role in regulating the accumulation of phenolic compounds under UV-B stress to help R. chrysanthum adapt. This study examines the impact of calcium-ion signaling on the accumulation of phenolic acid compounds, offering insights for future research on the molecular mechanisms underlying plant resilience to UV-B stress.

A constitutively monomeric UVR8 photoreceptor confers enhanced UV-B photomorphogenesis.

The plant ultraviolet-B (UV-B) photoreceptor UVR8 plays an important role in UV-B acclimation and survival. UV-B absorption by homodimeric UVR8 induces its monomerization and interaction with the E3 ubiquitin ligase COP1, leading ultimately to gene expression changes. UVR8 is inactivated through redimerization, facilitated by RUP1 and RUP2. Here, we describe a semidominant, hyperactive allele, namely uvr8-17D, that harbors a glycine-101 to serine mutation. UVR8G101S overexpression led to weak constitutive photomorphogenesis and extreme UV-B responsiveness. UVR8G101S was observed to be predominantly monomeric in vivo and, once activated by UV-B, was not efficiently inactivated. Analysis of a UVR8 crystal structure containing the G101S mutation revealed the distortion of a loop region normally involved in stabilization of the UVR8 homodimer. Plants expressing a UVR8 variant combining G101S with the previously described W285A mutation exhibited robust constitutive photomorphogenesis. This work provides further insight into UVR8 activation and inactivation mechanisms and describes a genetic tool for the manipulation of photomorphogenic responses.

A critical role of the soybean evening complex in the control of photoperiod sensitivity and adaptation.

Photoperiod sensitivity is a key factor in plant adaptation and crop production. In the short-day plant soybean, adaptation to low latitude environments is provided by mutations at the J locus, which confer extended flowering phase and thereby improve yield. The identity of J as an ortholog of Arabidopsis ELF3, a component of the circadian evening complex (EC), implies that orthologs of other EC components may have similar roles. Here we show that the two soybean homeologs of LUX ARRYTHMO interact with J to form a soybean EC. Characterization of mutants reveals that these genes are highly redundant in function but together are critical for flowering under short day, where the lux1 lux2 double mutant shows extremely late flowering and a massively extended flowering phase. This phenotype exceeds that of any soybean flowering mutant reported to date, and is strongly reminiscent of the "Maryland Mammoth" tobacco mutant that featured in the seminal 1920 study of plant photoperiodism by Garner and Allard [W. W. Garner, H. A. Allard, J. Agric. Res. 18, 553-606 (1920)]. We further demonstrate that the J-LUX complex suppresses transcription of the key flowering repressor E1 and its two homologs via LUX binding sites in their promoters. These results indicate that the EC-E1 interaction has a central role in soybean photoperiod sensitivity, a phenomenon also first described by Garner and Allard. EC and E1 family genes may therefore constitute key targets for customized breeding of soybean varieties with precise flowering time adaptation, either by introgression of natural variation or generation of new mutants by gene editing.