Silencing Nicotiana attenuata LHY and ZTL alters circadian rhythms in flowers

Emission and Transcriptional Regulation of Aroma Variation in Oncidium Twinkle 'Red Fantasy' Under Diel Rhythm

Oncidium hybridum is one of the important cut-flowers in the world. However, the lack of aroma in its cut-flower varieties greatly limits the sustainable development of the Oncidium hybridum cut-flowers industry. This paper is an integral investigation of the diel pattern and influencing factors of the aroma release of Oncidium Twinkle 'Red Fantasy'. GC-MS analysis revealed that the release of 3-Carene peaked at 10:00, while Butyl tiglate and Prenyl senecioate did so at 14:00, with a diel rhythm. By analyzing the correlation network between aroma component synthesis and differentially expressed genes, 15 key structural genes were detected and regulated by multiple circadian rhythm-related transcription factors. Cluster-17371.18_TPS, Cluster-65495.1_TPS, Cluster-46699.0_TPS, Cluster-60935.10_DXS, Cluster-47205.4_IDI, and Cluster-65313.7_LOX were key genes in the terpenoid and fatty acid derivative biosynthetic pathway, which were co-expressed with aroma release. Constant light/dark treatments revealed that the diurnal release of 3-Carene may be influenced by light and the circadian clock, and Butyl tiglate and Prenyl senecioate may be mainly determined by endogenous circadian clock. Under constant light treatment, the TPS, DXS, IDI, and LOX genes seem to lose their regulatory role in the release of aroma compounds from Oncidium Twinkle 'Red Fantasy'. Under constant dark treatment, the TPS genes were consistent with the release pattern of 3-Carene, which may be a key factor in regulating the diel rhythm of 3-Carene biosynthesis. These results laid a theoretical foundation for the study of floral transcriptional regulation and genetic engineering technology breeding of Oncidium hybridum.

A jasmonate-mediated regulatory network modulates diurnal floret opening time in rice

Diurnal floret opening time (DFOT) is a pivotal trait for successful fertilization and hybrid breeding in rice. However, the molecular mechanism underlying this trait is poorly understood in rice. In this study, we combined the cytological, genetic and molecular studies to demonstrate that jasmonic acid (JA) regulates DFOT in rice through modulating the turgor and osmotic pressure of the lodicules. We show that lodicules undergo dramatic morphologic changes, accompanied by changes in water and sugar contents during the process of floret opening. Consistently, a large set of genes associated with cell osmolality and cell wall remodeling exhibits distinct expression profiles at different time points in our time-course transcriptomes of lodicules. Notably, a group of JA biosynthesis and signaling genes is continuously upregulated, accompanied by a gradual increase in JA accumulation as floret opening approaching. Furthermore, we demonstrate that the JA biosynthesis gene OsAOS1 is required for endogenous JA biosynthesis in lodicules and promoting rice DFOT. Moreover, OsMYC2, a master regulator of JA signaling, regulates rice DFOT by directly activating OsAOS1, OsSWEET4, OsPIP2;2 and OsXTH9. Collectively, our findings establish a core regulatory network mediated by JA for modulating rice DFOT and provide effective gene targets for the genetic improvement of DFOT in rice.

Unlocking Nature's Rhythms: Insights into Secondary Metabolite Modulation by the Circadian Clock

Plants, like many other living organisms, have an internal timekeeper, the circadian clock, which allows them to anticipate photoperiod rhythms and environmental stimuli to optimally adjust plant growth, development, and fitness. These fine-tuned processes depend on the interaction between environmental signals and the internal interactive metabolic network regulated by the circadian clock. Although primary metabolites have received significant attention, the impact of the circadian clock on secondary metabolites remains less explored. Transcriptome analyses revealed that many genes involved in secondary metabolite biosynthesis exhibit diurnal expression patterns, potentially enhancing stress tolerance. Understanding the interaction mechanisms between the circadian clock and secondary metabolites, including plant defense mechanisms against stress, may facilitate the development of stress-resilient crops and enhance targeted management practices that integrate circadian agricultural strategies, particularly in the face of climate change. In this review, we will delve into the molecular mechanisms underlying circadian rhythms of phenolic compounds, terpenoids, and N-containing compounds.

The Circadian Clock Gene PHYTOCLOCK1 Mediates the Diurnal Emission of the Anti-Insect Volatile Benzyl Nitrile from Damaged Tea (Camellia sinensis) Plants

Benzyl nitrile from tea plants attacked by various pests displays a diurnal pattern, which may be closely regulated by the endogenous circadian clock. However, the molecular mechanism by the circadian clock of tea plants that regulates the biosynthesis and release of volatiles remains unclear. In this study, the circadian clock gene CsPCL1 can activate both the expression of the benzyl nitrile biosynthesis-related gene CsCYP79 and the jasmonic acid signaling-related transcription factor CsMYC2 involved in upregulating CsCYP79 gene, thereby resulting in the accumulation and release of benzyl nitrile. Therefore, the anti-insect function of benzyl nitrile was explored in the laboratory. The application of slow-release beads of benzyl nitrile in tea plantations significantly reduced the number of tea geometrids and had positive effects on the yield of fresh tea leaves. These findings reveal the potential utility of herbivore-induced plant volatiles for the green control of pests in tea plantations.

Evaluating the Adaptive Fitness of Circadian Clocks and their Evolution

Surely most chronobiologists believe circadian clocks are an adaptation of organisms that enhances fitness, but are we certain that this focus of our research effort really confers a fitness advantage? What is the evidence, and how do we evaluate it? What are the best criteria? These questions are the topic of this review. In addition, we will discuss selective pressures that might have led to the historical evolution of circadian systems while considering the intriguing question of whether the ongoing climate change is modulating these selective pressures so that the clock is still evolving.

Multiomics Analysis Reveals the Involvement of JsLHY in Controlling Aroma Production in Jasmine Flowers

The Jasminum sambac flower is famous for its rich fragrance. However, our knowledge of the regulatory network for its aroma formation remains largely unknown and therefore needs further study. To this end, an integrated analysis of the volatilomics and transcriptomics of jasmine flowers at different flowering stages was performed. The results revealed many candidate transcription factors (TFs) may be involved in regulating the aroma formation of jasmine, among which the MYB-related TF LATE ELONGATED HYPOCOTYL (JsLHY) was identified as a hub gene. Using the DNA affinity purification sequencing method, dual-luciferase reporter, and yeast one-hybrid assays, we demonstrate that JsLHY can bind the gene promoter regions of six aroma-related structural genes (JsBEAT1, JsTPS34, JsCNL6, JsBPBT, JsAAAT5, and Js4CL7) and directly promote their expression. In addition, suppressing JsLHY expression decreased both the expression of JsLHY-bound genes and the content of related VOCs. The present study reveals how JsLHY participates in jasmine aroma formation.

The circadian clock controls temporal and spatial patterns of floral development in sunflower

Biological rhythms are ubiquitous. They can be generated by circadian oscillators, which produce daily rhythms in physiology and behavior, as well as by developmental oscillators such as the segmentation clock, which periodically produces modular developmental units. Here, we show that the circadian clock controls the timing of late-stage floret development, or anthesis, in domesticated sunflowers. In these plants, up to thousands of individual florets are tightly packed onto a capitulum disk. While early floret development occurs continuously across capitula to generate iconic spiral phyllotaxy, during anthesis floret development occurs in discrete ring-like pseudowhorls with up to hundreds of florets undergoing simultaneous maturation. We demonstrate circadian regulation of floral organ growth and show that the effects of light on this process are time-of-day dependent. Delays in the phase of floral anthesis delay morning visits by pollinators, while disruption of circadian rhythms in floral organ development causes loss of pseudowhorl formation and large reductions in pollinator visits. We therefore show that the sunflower circadian clock acts in concert with environmental response pathways to tightly synchronize the anthesis of hundreds of florets each day, generating spatial patterns on the developing capitulum disk. This coordinated mass release of floral rewards at predictable times of day likely promotes pollinator visits and plant reproductive success.

Evolution of circadian clocks along the green lineage

Circadian clocks govern temporal programs in the green lineage (Chloroplastida) as they do in other photosynthetic pro- and eukaryotes, bacteria, fungi, animals, and humans. Their physiological properties, including entrainment, phase responses, and temperature compensation, are well conserved. The involvement of transcriptional/translational feedback loops in the oscillatory machinery and reversible phosphorylation events are also maintained. Circadian clocks control a large variety of output rhythms in green algae and terrestrial plants, adjusting their metabolism and behavior to the day-night cycle. The angiosperm Arabidopsis (Arabidopsis thaliana) represents a well-studied circadian clock model. Several molecular components of its oscillatory machinery are conserved in other Chloroplastida, but their functions may differ. Conserved clock components include at least one member of the CIRCADIAN CLOCK ASSOCIATED1/REVEILLE and one of the PSEUDO RESPONSE REGULATOR family. The Arabidopsis evening complex members EARLY FLOWERING3 (ELF3), ELF4, and LUX ARRHYTHMO are found in the moss Physcomitrium patens and in the liverwort Marchantia polymorpha. In the flagellate chlorophyte alga Chlamydomonas reinhardtii, only homologs of ELF4 and LUX (named RHYTHM OF CHLOROPLAST ROC75) are present. Temporal ROC75 expression in C. reinhardtii is opposite to that of the angiosperm LUX, suggesting different clock mechanisms. In the picoalga Ostreococcus tauri, both ELF genes are missing, suggesting that it has a progenitor circadian "green" clock. Clock-relevant photoreceptors and thermosensors vary within the green lineage, except for the CRYPTOCHROMEs, whose variety and functions may differ. More genetically tractable models of Chloroplastida are needed to draw final conclusions about the gradual evolution of circadian clocks within the green lineage.

Effects of Food Availability Cycles on Phase and Period of Activity-rest Rhythm in Drosophila melanogaster

Foraging and feeding are indispensable for survival and their timing depends not only on the metabolic state of the animal but also on the availability of food resources in their environment. Since both these aspects are subject to change over time, these behaviors exhibit rhythmicity in occurrence. As the locomotor activity of an organism is related to its disposition to acquire food, and peak feeding in fruit flies has been shown to occur at a particular time of the day, we asked if cyclic food availability can entrain their rhythmic activity. By subjecting flies to cyclic food availability, that is, feeding-starvation (FS) cycles, we provided food cues contrasting to the preferred activity times and observed if this imposed cycling in food availability could entrain the activity-rest rhythm. We found that phase control, which is a property integral to entrainment, was not achieved despite increasing starvation duration of FS cycles (FS 12:12, FS 10:14, and FS 8:16). We also found that flies subjected to T21 and T26 FS cycles were unable to match period of the activity rhythm to short or long T-cycles. Taken together, these results show that external food availability cycles do not entrain the activity-rest rhythm of fruit flies. However, we find that starvation-induced hyperactivity causes masking which results in phase changes. In addition, T-cycle experiments resulted in minor period changes during FS treatment. These findings highlight that food cyclicity by itself may not be a potent zeitgeber but may act in unison with other abiotic factors like light and temperature to help flies time their activity appropriately.

Real-Time Visualization of Scent Accumulation Reveals the Frequency of Floral Scent Emissions

Flowers emit a bouquet of volatiles to attract pollinators or to protect flowers from pathogen and herbivore attacks. Most floral volatiles are synthesized in the cytoplasm of petals and released into the headspace at a specific time of day. Various floral scent sampling methods coupled with gas chromatography-mass spectrometry have been used to measure the quality and quantity of floral volatiles. However, little is known about the emission patterns of floral scents. In most cases, it is still unclear whether floral scents emit continuously or discontinuously. Here we measured the frequency with which lily flowers emit scents using optical interferometry. By analyzing the refractive index difference between volatile organic compounds and ambient air, we were able to visualize the accumulation of the volatile vapors. The frequency of volatile emission was calculated from the unique footprint of temporal power spectrum maps. Based on these real-time measurements, we found that lily flowers emit the volatile compounds discontinuously, with pulses observed around every 10-50 min.

Circadian clock in plants: Linking timing to fitness

Endogenous circadian clock integrates cyclic signals of environment and daily and seasonal behaviors of organisms to achieve spatiotemporal synchronization, which greatly improves genetic diversity and fitness of species. This review addresses recent studies on the plant circadian system in the field of chronobiology, covering topics on molecular mechanisms, internal and external Zeitgebers, and hierarchical regulation of physiological outputs. The architecture of the circadian clock involves the autoregulatory transcriptional feedback loops, post-translational modifications of core oscillators, and epigenetic modifications of DNA and histones. Here, light, temperature, humidity, and internal elemental nutrients are summarized to illustrate the sensitivity of the circadian clock to timing cues. In addition, the circadian clock runs cell-autonomously, driving independent circadian rhythms in various tissues. The core oscillators responds to each other with biochemical factors including calcium ions, mineral nutrients, photosynthetic products, and hormones. We describe clock components sequentially expressed during a 24-h day that regulate rhythmic growth, aging, immune response, and resistance to biotic and abiotic stresses. Notably, more data have suggested the circadian clock links chrono-culture to key agronomic traits in crops.

Single-cell RNA-sequencing of Nicotiana attenuata corolla cells reveals the biosynthetic pathway of a floral scent

High-throughput single-cell RNA sequencing (scRNA-Seq) identifies distinct cell populations based on cell-to-cell heterogeneity in gene expression. By examining the distribution of the density of gene expression profiles, we can observe the metabolic features of each cell population. Here, we employ the scRNA-Seq technique to reveal the entire biosynthetic pathway of a flower volatile. The corolla of the wild tobacco Nicotiana attenuata emits a bouquet of scents that are composed mainly of benzylacetone (BA). Protoplasts from the N. attenuata corolla limbs and throat cups were isolated at three different time points, and the transcript levels of > 16 000 genes were analyzed in 3756 single cells. We performed unsupervised clustering analysis to determine which cell clusters were involved in BA biosynthesis. The biosynthetic pathway of BA was uncovered by analyzing gene co-expression in scRNA-Seq datasets and by silencing candidate genes in the corolla. In conclusion, the high-resolution spatiotemporal atlas of gene expression provided by scRNA-Seq reveals the molecular features underlying cell-type-specific metabolism in a plant.

Light-Quality Manipulation to Control Plant Growth and Photomorphogenesis in Greenhouse Horticulture: The State of the Art and the Opportunities of Modern LED Systems

Light quantity (intensity and photoperiod) and quality (spectral composition) affect plant growth and physiology and interact with other environmental parameters and cultivation factors in determining the plant behaviour. More than providing the energy for photosynthesis, light also dictates specific signals which regulate plant development, shaping and metabolism, in the complex phenomenon of photomorphogenesis, driven by light colours. These are perceived even at very low intensity by five classes of specific photoreceptors, which have been characterized in their biochemical features and physiological roles. Knowledge about plant photomorphogenesis increased dramatically during the last years, also thanks the diffusion of light-emitting diodes (LEDs), which offer several advantages compared to the conventional light sources, such as the possibility to tailor the light spectrum and to regulate the light intensity, depending on the specific requirements of the different crops and development stages. This knowledge could be profitably applied in greenhouse horticulture to improve production schedules and crop yield and quality. This article presents a brief overview on the effects of light spectrum of artificial lighting on plant growth and photomorphogenesis in vegetable and ornamental crops, and on the state of the art of the research on LEDs in greenhouse horticulture. Particularly, we analysed these effects by approaching, when possible, each single-light waveband, as most of the review works available in the literature considers the influence of combined spectra.

Why flowers close at noon? A case study of an alpine species Gentianopsis paludosa (Gentianaceae)

Repeatable floral closure with diurnal rhythms, that is, flower opening in the morning and closing in the evening, was widely reported. However, the rhythm of flower opening in the morning but closing in the midday received much less attention. Gentianopsis paludosa, Gentianaceae, has an obvious petal movement rhythm opening in the morning and closing at noon at northeast of the Qinghai-Tibetan Plateau. In this study, we examined the effects of temperature (T), relative humidity (RH), and illumination intensity (II) on G. paludosa's flower closure. Furthermore, we monitored the environmental changes inside and outside of the flowers, aiming to test the effect of floral closure on the stability of microenvironment inside the flower. Finally, we artificially interrupted temporal petal closure and investigated its effects on reproductive fitness. The results showed that high/low temperature contributed more to the flower closure than low RH, while illumination intensity had no significant effect on it. The medium temperature, relative humidity and illumination intensity (environmental conditions at 10:00) did not delay flower closure when flowers at pre-closing period or stimulate reopen when flowers full closed. Floral closure provided a stable temperature condition and a higher RH condition inside the flower. Meanwhile, compulsive opening and delayed closure of flowers decreased the seed-set ratio while no effect was found when flowers were forced to close. We conclude that endogenous rhythm regulates floral closure. The rhythm of petal movement providing a stable microenvironment for G. paludosa, increasing the seed production and saving energy from flower opening maintenance, which might be an adaptive strategy to against unfavorable environmental conditions.

PacBio and Illumina RNA Sequencing Identify Alternative Splicing Events in Response to Cold Stress in Two Poplar Species

In eukaryotes, alternative splicing (AS) is a crucial regulatory mechanism that modulates mRNA diversity and stability. The contribution of AS to stress is known in many species related to stress, but the posttranscriptional mechanism in poplar under cold stress is still unclear. Recent studies have utilized the advantages of single molecular real-time (SMRT) sequencing technology from Pacific Bioscience (PacBio) to identify full-length transcripts. We, therefore, used a combination of single-molecule long-read sequencing and Illumina RNA sequencing (RNA-Seq) for a global analysis of AS in two poplar species (Populus trichocarpa and P. ussuriensis) under cold stress. We further identified 1,261 AS events in P. trichocarpa and 2,101 in P. ussuriensis among which intron retention, with a frequency of more than 30%, was the most prominent type under cold stress. RNA-Seq data analysis and annotation revealed the importance of calcium, abscisic acid, and reactive oxygen species signaling in cold stress response. Besides, the low temperature rapidly induced multiple splicing factors, transcription factors, and differentially expressed genes through AS. In P. ussuriensis, there was a rapid occurrence of AS events, which provided a new insight into the complexity and regulation of AS during cold stress response in different poplar species for the first time.

Circadian Clock in Arabidopsis thaliana Determines Flower Opening Time Early in the Morning and Dominantly Closes Early in the Afternoon

Many plant species exhibit diurnal flower opening and closing, which is an adaptation influenced by the lifestyle of pollinators and herbivores. However, it remains unclear how these temporal floral movements are modulated. To clarify the role of the circadian clock in flower movement, we examined temporal floral movements in Arabidopsis thaliana. Wild-type (accessions; Col-0, Ler-0 and Ws-4) flowers opened between 0.7 and 1.4 h in a 16-h light period and closed between 7.5 and 8.3 h in a diurnal light period. In the arrhythmic mutants pcl1-1 and prr975, the former flowers closed slowly and imperfectly and the latter ones never closed. Under continuous light conditions, new flowers emerged and opened within a 23-26 h window in the wild-type, but the flowers in pcl1-1 and prr975 developed straight petals, whose curvatures were extremely small. Anti-phasic circadian gene expression of CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), LATE ELONGATED HYPOCOTYLE (LHY) and TIMING OF CAB EXPRESSION 1 (TOC1) occurred in wild-type flowers, but non-rhythmic expression was observed in pcl1-1 and prr975 mutants. Focusing on excised petals, bioluminescence monitoring revealed rhythmic promoter activities of genes expressed (CCA1, LHY and PHYTOCLOCK 1/LUX ARRHYTHMO, PCL1/LUX) in the morning and evening. These results suggest that the clock induces flower opening redundantly with unknown light-sensing pathways. By contrast, flower closing is completely dependent on clock control. These findings will lead to further exploration of the molecular mechanisms and evolutionary diversity of timing in flower opening and closing.

Morning and evening alarm of the circadian clock for flower opening times in Hemerocallis

Previous studies demonstrated that flower opening time (FOT) is a stable trait and precisely controlled by a circadian clock responsive to the environment. It plays a vital role in improving fertility. Hemerocallis spp. has different FOTs divided into two types: nocturnal and diurnal. To explore the regulatory mechanisms of their FOTs, we carried out a transcriptome sequencing experiment at different developmental stages of an F1 population with different FOTs. 55,883 unigenes were obtained, and 9234 differential genes were identified. Co-expression was analyzed by K-means clustering and weighted gene co-expression network analysis. Results showed that after entering reproductive growth, two FOT types of Hemerocallis had increased expression of genes related to photosynthetic metabolism and sensitivity to environmental response such as light and hormone signal transmission. Circadian rhythm-related activities were enriched in hub genes during the flowering stage. Genes showing differential expression between the two Hemerocallis groups were related to environmental response and photosynthesis pathways. Putative circadian clock genes displayed differences in expression across the flower opening stage in both groups of Hemerocallis. Twenty-three key circadian clock genes were identified, which related to sensitivity to light signal input and gating. These genes might closely relate to FOTs in Hemerocallis.

Flower orientation influences floral temperature, pollinator visits and plant fitness

Effective insect pollination requires appropriate responses to internal and external environmental cues in both the plant and the pollinator. Helianthus annuus, a highly outcrossing species, is marked for its uniform eastward orientation of mature pseudanthia, or capitula. Here we investigate how this orientation affects floral microclimate and the consequent effects on plant and pollinator interactions and reproductive fitness. We artificially manipulated sunflower capitulum orientation and temperature in both field and controlled conditions and assessed flower physiology, pollinator visits, seed traits and siring success. East-facing capitula were found to have earlier style elongation, pollen presentation and pollinator visits compared with capitula manipulated to face west. East-facing capitula also sired more offspring than west-facing capitula and under some conditions produced heavier and better-filled seeds. Local ambient temperature change on the capitulum was found to be a key factor regulating the timing of style elongation, pollen emergence and pollinator visits. These results indicate that eastward capitulum orientation helps to control daily rhythms in floral temperature, with direct consequences on the timing of style elongation and pollen emergence, pollinator visitation, and plant fitness.

Moths sense but do not learn flower odors with their proboscis during flower investigation

Insect pollinators, such as the tobacco hawkmoth Manduca sexta, are known for locating flowers and learning floral odors by using their antennae. A recent study revealed, however, that the tobacco hawkmoth additionally possesses olfactory sensilla at the tip of its proboscis. Here, we asked whether this second ‘nose’ of the hawkmoth is involved in odor learning, similar to the antennae. We first show that M. sexta foraging efficiency at Nicotiana attenuata flowers increases with experience. This raises the question whether olfactory learning with the proboscis plays a role during flower handling. By rewarding the moths at an artificial flower, we show that, although moths learn an odor easily when they perceive it with their antennae, experiencing the odor just with the proboscis is not sufficient for odor learning. Furthermore, experiencing the odor with the antennae during training does not affect the behavior of the moths when they later detect the learned odor with the proboscis only. Therefore, there seems to be no cross-talk between the antennae and proboscis, and information learnt by the antennae cannot be retrieved by the proboscis.

Highlighted Article: The hawkmoth Manduca sexta is able to detect odors with the tip of its tongue: this ‘second nose’ is not used for olfactory learning during flower investigation.

Molecular understanding of postharvest flower opening and senescence

Flowers are key organs in many ornamental plants, and various phases of flower development impact their economic value. The final stage of petal development is associated with flower senescence, which is an irreversible process involving programmed cell death, and premature senescence of cut flowers often results in major losses in quality during postharvest handling. Flower opening and senescence are two sequential processes. As flowers open, the stamens are exposed to attract pollinators. Once pollination occurs, flower senescence is initiated. Both the opening and senescence processes are regulated by a range of endogenous phytohormones and environmental factors. Ethylene acts as a central regulator for the ethylene-sensitive flowers. Other phytohormones, including auxin, gibberellin, cytokinin, jasmonic acid and abscisic acid, are also involved in the control of petal expansion and senescence. Water status also directly influences postharvest flower opening, while pollination is a key event in initiating the onset flower senescence. Here, we review the current understanding of flower opening and senescence, and propose future research directions, such as the study of interactions between hormonal and environmental signals, the application of new technology, and interdisciplinary research.

Variation in Manduca sexta Pollination-Related Floral Traits and Reproduction in a Wild Tobacco Plant

Most flowering plants depend on animal pollination for successful sexual reproduction. Floral signals such as color, shape, and odor are crucial in establishing this (often mutualistic) interaction. Plant and pollinator phenotypes can vary temporally but also spatially, thus creating mosaic-like patterns of local adaptations. Here, we investigated natural variation in floral morphology, flower volatile emission, and phenology in four accessions of a self-compatible wild tobacco, Nicotiana attenuata, to assess how these traits match the sensory perception of a known pollinator, the hawkmoth Manduca sexta. These accessions differ in floral traits and also in their habitat altitudes. Based on habitat temperatures, the accession occurring at the highest altitude (California) is less likely to be visited by M. sexta, while the others (Arizona, Utah 1, and Utah 2) are known to receive M. sexta pollinations. The accessions varied significantly in flower morphologies, volatile emissions, flower opening, and phenology, traits likely important for M. sexta perception and floral handling. In wind tunnel assays, we assessed the seed set of emasculated flowers after M. sexta visitation and of natural selfed and hand-pollinated selfed flowers. After moth visitations, plants of two accessions (Arizona and Utah 2) produced more capsules than the other two, consistent with predictions that accessions co-occurring with M. sexta would benefit more from the pollination services of this moth. We quantified flower and capsule production in four accessions in a glasshouse assay without pollinators to assess the potential for self-pollination. The two Utah accessions set significantly more seeds after pollen supplementation compared with those of autonomous selfing flowers, suggesting a greater opportunistic benefit from efficient pollinators than the other two. Moreover, emasculated flowers of the accession with the most exposed stigma (Utah 2) produced the greatest seed set after M. sexta visitation. This study reveals intraspecific variation in pollination syndromes that illuminate the potential of a plant species to adapt to local pollinator communities, changing environments, and altered pollination networks.

Transcriptome Profile Analysis of Strawberry Leaves Reveals Flowering Regulation under Blue Light Treatment

Blue light is an important signal that regulates the flowering of strawberry plants. To reveal the mechanism of early flowering under blue light treatment at the transcriptional regulation level, seedlings of cultivated strawberry (Fragaria × ananassa Duch.) "Benihoppe" were subjected to a white light treatment (WL) and blue light treatment (BL) until their flowering. To detect the expression patterns of genes in response to BL, a transcriptome analysis was performed based on RNA-Seq. The results identified a total of 6875 differentially expressed genes (DEGs) that responded to BL, consisting of 3138 (45.64%) downregulated ones and 3737 (54.36%) upregulated ones. These DEGs were significantly enriched into 98 GO terms and 71 KEGG pathways based on gene function annotation. Among the DEGs, the expression levels of genes that might participate in light signaling (PhyB, PIFs, and HY5) and circadian rhythm (FKF1, CCA1, LHY, and CO) in plants were altered under BL. The BBX transcription factors which responded to BL were also identified. The result showed that the FaBBX29, one of strawberry's BBX family genes, may play an important role in flowering regulation. Our results provide a timely, comprehensive view and a reliable reference data resource for further study of flowering regulation under different light qualities.

Chronoculture, harnessing the circadian clock to improve crop yield and sustainability

Human health is dependent on a plentiful and nutritious supply of food, primarily derived from crop plants. Rhythmic supply of light as a result of the day and night cycle led to the evolution of circadian clocks that modulate most plant physiology, photosynthesis, metabolism, and development. To regulate crop traits and adaptation, breeders have indirectly selected for variation at circadian genes. The pervasive impact of the circadian system on crops suggests that future food production might be improved by modifying circadian rhythms, engineering the timing of transgene expression, and applying agricultural treatments at the most effective time of day. We describe the applied research required to take advantage of circadian biology in agriculture to increase production and reduce inputs.

The Effect of Post-harvest Conditions in Narcissus sp. Cut Flowers Scent Profile

Narcissus flowers are used as cut flowers and to obtain high quality essential oils for the perfume industry. As a winter crop in the Mediterranean area, it flowers at temperatures ranging between 10 and 15°C during the day and 3-10°C during the night. Here we tested the impact of different light and temperature conditions on scent quality during post-harvest. These two types of thermoperiod and photoperiod. We also used constant darkness and constant temperatures. We found that under conditions of 12:12 Light Dark and 15-5°C, Narcissus emitted monoterpenes and phenylpropanoids. Increasing the temperature to 20°-10°C in a 12:12 LD cycle caused the loss of cinnamyl acetate and emission of indole. Under constant dark, there was a loss of scent complexity. Constant temperatures of 20°C caused a decrease of scent complexity that was more dramatic at 5°C, when the total number of compounds emitted decreased from thirteen to six. Distance analysis confirmed that 20°C constant temperature causes the most divergent scent profile. We found a set of four volatiles, benzyl acetate, eucalyptol, linalool, and ocimene that display a robust production under differing environmental conditions, while others were consistently dependent on light or thermoperiod. Scent emission changed significantly during the day and between different light and temperature treatments. Under a light:dark cycle and 15-5°C the maximum was detected during the light phase but this peak shifted toward night under 20-10°C. Moreover, under constant darkness the peak occurred at midnight and under constant temperature, at the end of night. Using Machine Learning we found that indole was the volatile with a highest ranking of discrimination followed by D-limonene. Our results indicate that light and temperature regimes play a critical role in scent quality. The richest scent profile is obtained by keeping flowers at 15°-5°C thermoperiod and a 12:12 Light Dark photoperiod.

Plant Volatile Organic Compounds Evolution: Transcriptional Regulation, Epigenetics and Polyploidy

Volatile organic compounds (VOCs) are emitted by plants as a consequence of their interaction with biotic and abiotic factors, and have a very important role in plant evolution. Floral VOCs are often involved in defense and pollinator attraction. These interactions often change rapidly over time, so a quick response to those changes is required. Epigenetic factors, such as DNA methylation and histone modification, which regulate both genes and transcription factors, might trigger adaptive responses to these evolutionary pressures as well as regulating the rhythmic emission of VOCs through circadian clock regulation. In addition, transgenerational epigenetic effects and whole genome polyploidy could modify the generation of VOCs’ profiles of offspring, contributing to long-term evolutionary shifts. In this article, we review the available knowledge about the mechanisms that may act as epigenetic regulators of the main VOC biosynthetic pathways, and their importance in plant evolution.

Exposure to Artificial Light at Night and the Consequences for Flora, Fauna, and Ecosystems

The present review draws together wide-ranging studies performed over the last decades that catalogue the effects of artificial-light-at-night (ALAN) upon living species and their environment. We provide an overview of the tremendous variety of light-detection strategies which have evolved in living organisms - unicellular, plants and animals, covering chloroplasts (plants), and the plethora of ocular and extra-ocular organs (animals). We describe the visual pigments which permit photo-detection, paying attention to their spectral characteristics, which extend from the ultraviolet into infrared. We discuss how organisms use light information in a way crucial for their development, growth and survival: phototropism, phototaxis, photoperiodism, and synchronization of circadian clocks. These aspects are treated in depth, as their perturbation underlies much of the disruptive effects of ALAN. The review goes into detail on circadian networks in living organisms, since these fundamental features are of critical importance in regulating the interface between environment and body. Especially, hormonal synthesis and secretion are often under circadian and circannual control, hence perturbation of the clock will lead to hormonal imbalance. The review addresses how the ubiquitous introduction of light-emitting diode technology may exacerbate, or in some cases reduce, the generalized ever-increasing light pollution. Numerous examples are given of how widespread exposure to ALAN is perturbing many aspects of plant and animal behaviour and survival: foraging, orientation, migration, seasonal reproduction, colonization and more. We examine the potential problems at the level of individual species and populations and extend the debate to the consequences for ecosystems. We stress, through a few examples, the synergistic harmful effects resulting from the impacts of ALAN combined with other anthropogenic pressures, which often impact the neuroendocrine loops in vertebrates. The article concludes by debating how these anthropogenic changes could be mitigated by more reasonable use of available technology - for example by restricting illumination to more essential areas and hours, directing lighting to avoid wasteful radiation and selecting spectral emissions, to reduce impact on circadian clocks. We end by discussing how society should take into account the potentially major consequences that ALAN has on the natural world and the repercussions for ongoing human health and welfare.

ZEITLUPE is required for shade avoidance in the wild tobacco Nicotiana attenuata

Being shaded is a common environmental stress for plants, especially for densely planted crops. Shade decreases red: far-red (R:FR) ratios that inactivate phytochrome B (PHYB) and subsequently release p̱hytochrome i̱nteraction f̱actors (PIFs). Shaded plants display elongated hypocotyls, internodes, and petioles, hyponastic leaves, early flowering and are inhibited in branching: traits collectively called the shade avoidance syndrome (SAS). ZEITLUPE (ZTL) is a circadian clock component and blue light photoreceptor, which is also involved in floral rhythms and plant defense in Nicotiana attenuata. ztl mutants are hypersensitive to red light and ZTL physically interacts with PHYB, suggesting the involvement of ZTL in R:FR light signaling. Here, we show that N. attenuata ZTL-silenced plants display a phenotype opposite to that of the SAS under normal light. After simulated shade, the normally induced transcript levels of the SAS marker gene, ATHB2 are attenuated in ZTL-silenced plants. The auxin signaling pathway, known to be involved in SAS, was also significantly attenuated. Furthermore, NaZTL directly interacts with NaPHYBs, and regulates the transcript levels of PHYBs, PIF3a, PIF7 and PIF8 under shade. Our results suggest that ZTL may regulate PHYB- and the auxin-mediated signaling pathway, which functions in the SAS of N. attenuata.

Floral Scent Composition and Fine-Scale Timing in Two Moth-Pollinated Hawaiian Schiedea (Caryophyllaceae)

Floral scent often intensifies during periods of pollinator activity, but the degree of this synchrony may vary among scent compounds depending on their function. Related plant species with the same pollinator may exhibit similar timing and composition of floral scent. We compared timing and composition of floral volatiles for two endemic Hawaiian plant species, Schiedea kaalae and S. hookeri (Caryophyllaceae). For S. kaalae, we also compared the daily timing of emission of floral volatiles to evening visits of their shared pollinator, an endemic Hawaiian moth (Pseudoschrankia brevipalpis; Erebidae). The identity and amount of floral volatiles were measured in the greenhouse during day and evening periods with dynamic headspace sampling and GC-MS (gas chromatography - mass spectrometry). The timing of emissions (daily rise, peak, and fall) was measured by sampling continuously for multiple days in a growth chamber with PTR-MS (proton transfer reaction mass spectrometry). Nearly all volatiles detected underwent strong daily cycles in emission. Timings of floral volatile emissions were similar for S. kaalae and S. hookeri, as expected for two species sharing the same pollinator. For S. kaalae, many volatiles known to attract moths, including several linalool oxides and 2-phenylacetaldehyde, peaked within 2 h of the peak visitation time of the moth which pollinates both species. Floral volatiles of both species that peaked in the evening were also emitted several hours before and after the brief window of pollinator activity. Few volatiles followed a daytime emission pattern, consistent with increased apparency to visitors only at night. The scent blends of the two species differed in their major components and were most distinct from each other in the evening. The qualitative difference in evening scent composition between the two Schiedea species may reflect their distinct evolutionary history and may indicate that the moth species uses several different floral cues to locate rewards.

ZEITLUPE facilitates the rhythmic movements of Nicotiana attenuata flowers

Circadian organ movements are ubiquitous in plants. These rhythmic outputs are thought to be regulated by the circadian clock and auxin signalling, but the underlying mechanisms have not been clarified. Flowers of Nicotiana attenuata change their orientation during the daytime through a 140° arc to balance the need for pollinators and the protection of their reproductive organs. This rhythmic trait is under the control of the circadian clock and results from bending and re-straightening movements of the pedicel, stems that connect flowers to the inflorescence. Using an explant system that allowed pedicel growth and curvature responses to be characterized with high spatial and temporal resolution, we demonstrated that this movement is organ autonomous and mediated by auxin. Changes in the growth curvature of the pedicel are accompanied by an auxin gradient and dorsiventral asymmetry in auxin-dependent transcriptional responses; application of auxin transport inhibitors influenced the normal movements of this organ. Silencing the expression of the circadian clock component ZEITLUPE (ZTL) arrested changes in the growth curvature of the pedicel and altered auxin signalling and responses. IAA19-like, an Aux/IAA transcriptional repressor that is circadian regulated and differentially expressed between opposite tissues of the pedicel, and therefore possibly involved in the regulation of changes in organ curvature, physically interacted with ZTL. Together, these results are consistent with a direct link between the circadian clock and the auxin signalling pathway in the regulation of this rhythmic floral movement.

The circadian clock coordinates plant development through specificity at the tissue and cellular level

The circadian clock is a genetic circuit that allows organisms to anticipate daily events caused by the rotation of the Earth. The plant clock regulates physiology at multiple scales, from cell division to ecosystem-scale interactions. It is becoming clear that rather than being a single perfectly synchronised timer throughout the plant, the clock can be sensitive to different cues, run at different speeds, and drive distinct processes in different cell types and tissues. This flexibility may help the plant clock to regulate such a range of developmental and physiological processes. In this review, using examples from the literature, we describe how the clock regulates development at multiple scales and discuss how the clock might allow local flexibility in regulation whilst remaining coordinated across the plant.

The clock gene Gigantea 1 from Petunia hybrida coordinates vegetative growth and inflorescence architecture

The gene GIGANTEA (GI) appeared early in land plants. It is a single copy gene in most plants and is found in two to three copies in Solanaceae. We analyzed the silencing of one GI copy, Petunia hybrida GI1 (PhGI1), by hairpin RNAs in Petunia in order to gain knowledge about its range of functions. Decreased transcript levels of PhGI1 were accompanied also by a reduction of PhGI2. They were further associated with increased time period between two consecutive peaks for PhGI1 and CHANEL (PhCHL), the orthologue of the blue light receptor gene ZEITLUPE (ZTL), confirming its role in maintaining circadian rhythmicity. Silenced plants were bigger with modified internode length and increased leaf size while flowering time was not altered. We uncovered a new function for PhGI1 as silenced plants showed reduction of flower bud number and the appearance of two flower buds in the bifurcation point, were normally one flower bud and the inflorescence meristem separate. Furthermore, one of the flower buds consistently showed premature flower abortion. Flowers that developed fully were significantly smaller as a result of decreased cell size. Even so the circadian pattern of volatile emission was unchanged in the silenced lines, flowers emitted 20% less volatiles on fresh weight basis over 24 hours and showed changes in the scent profile. Our results indicate a novel role of PhGI1 in the development of reproductive organs in Petunia. PhGI1 therefore represses growth in vegetative plant parts, maintains the typical cymose inflorescence structure, and inhibits premature flower abortion.

CRISPR/Cas9-mediated targeted mutagenesis of GmLHY genes alters plant height and internode length in soybean

BACKGROUND

Soybean (Glycine max) is an economically important oil and protein crop. Plant height is a key trait that significantly impacts the yield of soybean; however, research on the molecular mechanisms associated with soybean plant height is lacking. The CRISPR (clustered regularly interspaced short palindromic repeat)/Cas9 (CRISPR-associated system 9) system is a recently developed technology for gene editing that has been utilized to edit the genomes of crop plants.

RESULTS

Here, we designed four gRNAs to mutate four LATE ELONGATED HYPOCOTYL (LHY) genes in soybean. In order to test whether the gRNAs could perform properly in transgenic soybean plants, we first tested the CRISPR construct in transgenic soybean hairy roots using Agrobacterium rhizogenes strain K599. Once confirmed, we performed stable soybean transformation and obtained 19 independent transgenic soybean plants. Subsequently, we obtained one T1 transgene-free homozygous quadruple mutant of GmLHY by self-crossing. The phenotypes of the T2-generation transgene-free quadruple mutant plants were observed, and the results showed that the quadruple mutant of GmLHY displayed reduced plant height and shortened internodes. The levels of endogenous gibberellic acid (GA3) in Gmlhy1a1b2a2b was lower than in the wild type (WT), and the shortened internode phenotype could be rescued by treatment with exogenous GA3. In addition, the relative expression levels of GA metabolic pathway genes in the quadruple mutant of GmLHY were significantly decreased in comparison to the WT. These results suggest that GmLHY encodes an MYB transcription factor that affects plant height through mediating the GA pathway in soybean. We also developed genetic markers for identifying mutants for application in breeding studies.

CONCLUSIONS

Our results indicate that CRISPR/Cas9-mediated targeted mutagenesis of four GmLHY genes reduces soybean plant height and shortens internodes from 20 to 35 days after emergence (DAE). These findings provide insight into the mechanisms underlying plant height regulatory networks in soybean.

Plant Cell-Cell Transport via Plasmodesmata Is Regulated by Light and the Circadian Clock

Plasmodesmata (PD) are essential for plant development, but little is known about their regulation. Several studies have linked PD transport to chloroplast-centered signaling networks, but the physiological significance of this connection remains unclear. Here, we show that PD transport is strongly regulated by light and the circadian clock. Light promotes PD transport during the day, but light is not sufficient to increase rates of PD transport at night, suggesting a circadian gating mechanism. Silencing expression of the core circadian clock gene, LHY/CCA1, allows light to strongly promote PD transport during subjective night, confirming that the canonical plant circadian clock controls the PD transport light response. We conclude that PD transport is dynamically regulated during the day/night cycle. Due to the many roles of PD in plant biology, this discovery has strong implications for plant development, physiology, and pathogenesis.

Circadian Regulation of the Plant Transcriptome Under Natural Conditions

Circadian rhythms produce a biological measure of the time of day. In plants, circadian regulation forms an essential adaptation to the fluctuating environment. Most of our knowledge of the molecular aspects of circadian regulation in plants is derived from laboratory experiments that are performed under controlled conditions. However, it is emerging that the circadian clock has complex roles in the coordination of the transcriptome under natural conditions, in both naturally occurring populations of plants and in crop species. In this review, we consider recent insights into circadian regulation under natural conditions. We examine how circadian regulation is integrated with the acute responses of plants to the daily and seasonally fluctuating environment that also presents environmental stresses, in order to coordinate the transcriptome and dynamically adapt plants to their continuously changing environment.

Transcriptional Structure of Petunia Clock in Leaves and Petals

The plant circadian clock coordinates environmental signals with internal processes including secondary metabolism, growth, flowering, and volatile emission. Plant tissues are specialized in different functions, and petals conceal the sexual organs while attracting pollinators. Here we analyzed the transcriptional structure of the petunia (Petunia x hybrida) circadian clock in leaves and petals. We recorded the expression of 13 clock genes in petunia under light:dark (LD) and constant darkness (DD). Under light:dark conditions, clock genes reached maximum expression during the light phase in leaves and the dark period in petals. Under free running conditions of constant darkness, maximum expression was delayed, especially in petals. Interestingly, the rhythmic expression pattern of PhLHY persisted in leaves and petals in LD and DD. Gene expression variability differed among leaves and petals, time of day and photoperiod. The transcriptional noise was higher especially in leaves under constant darkness. We found that PhPRR7, PhPRR5, and PhGI paralogs showed changes in gene structure including exon number and deletions of CCT domain of the PRR family. Our results revealed that petunia petals presented a specialized clock.

Novel Crosstalks between Circadian Clock and Jasmonic Acid Pathway Finely Coordinate the Tradeoff among Plant Growth, Senescence and Defense

Circadian clock not only functions as a cellular time-keeping mechanism, but also acts as a master regulator to coordinate the tradeoff between plant growth and defense in higher plants by timing a few kinds of phytohormone biosynthesis and signaling, including jasmonic acid (JA). Notably, circadian clock and JA pathway have recently been shown to intertwine with each other to ensure and optimize the plant fitness in an ever-changing environment. It has clearly demonstrated that there are multiple crosstalk pathways between circadian clock and JA at both transcriptional and post-transcriptional levels. In this scenario, circadian clock temporally modulates JA-mediated plant development events, herbivory resistance and susceptibility to pathogen. By contrast, the JA signaling regulates clock activity in a feedback manner. In this review, we summarized the cross networks between circadian clock and JA pathway at both transcriptional and post-transcriptional levels. We proposed that the novel crosstalks between circadian clock and JA pathway not only benefit for the understanding the JA-associated circadian outputs including leaf senescence, biotic, and abiotic defenses, but also put timing as a new key factor to investigate JA pathway in the future.

The Snapdragon LATE ELONGATED HYPOCOTYL Plays A Dual Role in Activating Floral Growth and Scent Emission

The plant circadian clock controls a large number of internal processes, including growth and metabolism. Scent emission displays a circadian pattern in many species such as the snapdragon. Here we show that knocking down LATE ELONGATED HYPOCOTYL in Antirrhinum majus affects growth and scent emission. In order to gain an understanding of the growth kinetics, we took a phenomic approach using in-house artificial vision systems, obtaining time-lapse videos. Wild type flowers showed a higher growth speed than knockdown plants. The maximal growth rate was decreased by 22% in plants with lower LHY expression. Floral volatiles were differentially affected as RNAi plants showed advanced emission of compounds synthesized from cinnamic acid and delayed emission of metabolites of benzoic acid. The monoterpenes myrcene and ocimene were delayed, whereas the sesquiterpene farnesene was advanced. Overall, transgenic lines showed an altered volatile emission pattern and displayed a modified scent profile. Our results show that AmLHY plays an important role in the quantitative and qualitative control of floral growth and scent emission.

The circadian clock contributes to diurnal patterns of plant indirect defense in nature

The plant circadian clock regulates the rhythms of plant metabolism. Many herbivore-induced plant volatiles (HIPVs) fluctuate, diurnally, but the role of the circadian clock in the emission of HIPVs and their ecological consequences remains largely unknown. Here, we show that the timing of herbivore attack can alter the outcome of tri-trophic interactions, and this is mediated by the circadian clock, under both field and glasshouse conditions. Although most HIPV emissions did not have a circadian rhythm, the circadian clock modulated HIPV emissions in a time-dependent manner. HIPVs mediate tri-trophic interactions, and the circadian clock may affect these interactions by modulating HIPV emission in nature.

Using natural variation to achieve a whole-plant functional understanding of the responses mediated by jasmonate signaling

The dramatic advances in our understanding of the molecular biology and biochemistry of jasmonate (JA) signaling have been the subject of several excellent recent reviews that have highlighted the phytohormonal function of this signaling pathway. Here, we focus on the responses mediated by JA signaling which have consequences for a plant's Darwinian fitness, i.e. the organism-level function of JA signaling. The most diverse module in the signaling cascade, the JAZ proteins, and their interactions with other proteins and transcription factors, allow this canonical signaling cascade to mediate a bewildering array of traits in different tissues at different times; the functional coherence of these diverse responses are best appreciated in an organismal/ecological context. From published work, it appears that jasmonates can function as the 'Swiss Army knife' of plant signaling, mediating many different biotic and abiotic stress and developmental responses that allow plants to contextualize their responses to their frequently changing local environments and optimize their fitness. We propose that a deeper analysis of the natural variation in both within-plant and within-population JA signaling components is a profitable means of attaining a coherent whole-plant functional perspective of this signaling cascade, and provide examples of this approach from the Nicotiana attenuata system.

Circadian Network Interactions with Jasmonate Signaling and Defense

Plants experience specific stresses at particular, but predictable, times of the day. The circadian clock is a molecular oscillator that increases plant survival by timing internal processes to optimally match these environmental challenges. Clock regulation of jasmonic acid (JA) action is important for effective defenses against fungal pathogens and generalist herbivores in multiple plant species. Endogenous JA levels are rhythmic and under clock control with peak JA abundance during the day, a time when plants are more likely to experience certain types of biotic stresses. The expression of many JA biosynthesis, signaling, and response genes is transcriptionally controlled by the clock and timed through direct connections with core clock proteins. For example, the promoter of Arabidopsis transcription factor MYC2, a master regulator for JA signaling, is directly bound by the clock evening complex (EC) to negatively affect JA processes, including leaf senescence, at the end of the day. Also, tobacco ZEITLUPE, a circadian photoreceptor, binds directly to JAZ proteins and stimulates their degradation with resulting effects on JA root-based defenses. Collectively, a model where JA processes are embedded within the circadian network at multiple levels is emerging, and these connections to the circadian network suggest multiple avenues for future research.

Time-series transcriptome provides insights into the gene regulation network involved in the volatile terpenoid metabolism during the flower development of lavender

BACKGROUND

Essential oils (EOs) of Lavandula angustifolia, mainly consist of monoterpenoids and sesquiterpenoids, are of great commercial value. The multi-flower spiciform thyrse of lavender not only determines the output of EOs but also reflects an environmental adaption strategy. With the flower development and blossom in turn, the fluctuation of the volatile terpenoids displayed a regular change at each axis. However, the molecular mechanism underlying the regulation of volatile terpenoids during the process of flowering is poorly understood in lavender. Here, we combine metabolite and RNA-Seq analyses of flowers of five developmental stages at first- and second-axis (FFDSFSA) and initial flower bud (FB0) to discover the active terpenoid biosynthesis as well as flowering-related genes.

RESULTS

A total of 56 mono- and sesquiterpenoids were identified in the EOs of L. angustifolia 'JX-2'. FB0' EO consists of 55 compounds and the two highest compounds, β-trans-ocimene (20.57%) and (+)-R-limonene (17.00%), can get rid of 74.71 and 78.41% aphids in Y-tube olfactometer experiments, respectively. With sequential and successive blossoms, temporally regulated volatiles were linked to pollinator attraction in field and olfaction bioassays. In three characteristic compounds of FFDSFSA' EOs, linalyl acetate (72.73%) and lavandulyl acetate (72.09%) attracted more bees than linalool (45.35%). Many transcripts related to flowering time and volatile terpenoid metabolism expressed differently during the flower development. Similar metabolic and transcriptomic profiles were observed when florets from the two axes were maintained at the same maturity grade. Besides both compounds and differentially expressed genes were rich in FB0, most volatile compounds were significantly correlated with FB0-specific gene module. Most key regulators related to flowering and terpenoid metabolism were interconnected in the subnetwork of FB0-specific module, suggesting the cross-talk between the two biological processes to some degree.

CONCLUSIONS

Characteristic compounds and gene expression profile of FB0 exhibit ecological value in pest control. The precise control of each-axis flowering and regular emissions at transcriptional and metabolic level are important to pollinators attraction for lavender. Our study sheds new light on lavender maximizes its fitness from "gene-volatile terpenoid-insect" three layers.

The Petunia CHANEL Gene is a ZEITLUPE Ortholog Coordinating Growth and Scent Profiles

The floral perianth, comprising sepals and petals, conceals the sexual organs and attracts pollinators. The coordination of growth and scent emission is not fully understood. We have analyzed the effect of knocking down CHANEL (PhCHL), the ZEITLUPE ortholog in petunia (PhCHL) by hairpin RNAs. Plants with low PhCHL mRNA had overall decreased size. Growth evaluation using time lapse image analysis showed that early leaf movement was not affected by RNAi:PhCHL, but flower angle movement was modified, moving earlier during the day in knockdown plants than in wild types. Despite differences in stem length, growth rate was not significantly affected by loss of PhCHL. In contrast, petal growth displayed lower growth rate in RNAi:PhCHL. Decreased levels of PhCHL caused strongly modified scent profiles, including changes in composition and timing of emission resulting in volatile profiles highly divergent from the wild type. Our results show a role of PhCHL in controlling growth and development of vegetative and reproductive organs in petunia. The different effects of PhCHL on organ development indicate an organ-specific interpretation of the down regulation of PhCHL. Through the control of both timing and quantitative volatile emissions, PhCHL appears to be a major coordinator of scent profiles.

Herbivory elicits changes in green leaf volatile production via jasmonate signaling and the circadian clock

The timing of plant volatile emissions is important for a robust indirect defense response. Green leaf volatiles (GLVs) are emitted by plants upon damage but can be suppressed by herbivore-associated elicitors, and the abundance and composition of GLVs vary depending on the timing of herbivore attack. We show that the GLV biosynthetic enzyme HYDROPEROXIDE LYASE (HPL) is transcriptionally regulated by the circadian clock in Nicotiana attenuata. In accordance with transcript abundance of NaHPL, GLV aldehyde pools in intact leaves peaked at night and at subjective night under diurnal and continuous light conditions, respectively. Moreover, although the basal abundance of NaHPL transcripts is upregulated by jasmonate (JA) signaling, JA does not regulate the reduction of NaHPL transcript abundance in damaged leaves by simulated herbivore treatment. Unexpectedly, the plant circadian clock was strongly altered when Manduca sexta larvae fed on N. attenuata, and this was also independent of JA signaling. Lastly, the temporal dynamics of NaHPL transcripts and total GLV emissions were strongly altered by M. sexta larval feeding. Our data suggest that the temporal dynamics of emitted GLV blends result from a combination of damage, JA signaling, herbivore-associated elicitors, and the plant circadian clock.

Flower movement balances pollinator needs and pollen protection

Flower signaling and orientation are key characteristics that determine a flower's pollinator guild. However, many flowers actively move during their daily cycle, changing both their detectability and accessibility to pollinators. The flowers of the wild tobacco Nicotiana attenuata orientate their corolla upward at sunset and downward after sunrise. Here, we investigated the effect of different flower orientations on a major pollinator of N. attenuata, the hawkmoth Manduca sexta. We found that although flower orientation influenced the flight altitude of the moth in respect to the flower, it did not alter the moth's final flower choice. These behavioral observations were consistent with the finding that orientation did not systematically change the spatial distribution of floral volatiles, which are major attractants for the moths. Moreover, hawkmoths invested the same amount of time into probing flowers at different orientations, even though they were only able to feed and gather pollen from horizontally and upward-oriented flowers, but not from downward-facing flowers. The orientation of the flower was hence crucial for a successful interaction between N. attenuata and its hawkmoth pollinator. Additionally, we also investigated potential adverse effects of exposing flowers at different orientations to natural daylight levels, finding that anther temperature of upward-oriented flowers was more than 7°C higher than for downward-oriented flowers. This increase in temperature likely caused the significantly reduced germination success that was observed for pollen grains from upward-oriented flowers in comparison to those of downward and horizontally oriented flowers. These results highlight the importance of flower reorientation to balance pollen protection and a successful interaction of the plant with its insect pollinators by maintaining the association between flower volatiles and flower accessibility to the pollinator.

Auxin controls circadian flower opening and closure in the waterlily

BACKGROUND

Flowers open at sunrise and close at sunset, establishing a circadian floral movement rhythm to facilitate pollination as part of reproduction. By the coordination of endogenous factors and environmental stimuli, such as circadian clock, photoperiod, light and temperature, an appropriate floral movement rhythm has been established; however, the underlying mechanisms remain unclear.

RESULTS

In our study, we use waterlily as a model which represents an early-diverging grade of flowering plants, and we aim to reveal the general mechanism of flower actions. We found that the intermediate segment of petal cells of waterlily are highly flexible, followed by a circadian cell expansion upon photoperiod stimuli. Auxin causes constitutively flower opening while auxin inhibitor suppresses opening event. Subsequent transcriptome profiles generated from waterlily's intermediate segment of petals at different day-time points showed that auxin is a crucial phytohormone required for floral movement rhythm via the coordination of YUCCA-controlled auxin synthesis, GH3-mediated auxin homeostasis, PIN and ABCB-dependent auxin efflux as well as TIR/AFB-AUX/IAA- and SAUR-triggered auxin signaling. Genes involved in cell wall organization were downstream of auxin events, resulting in the output phenotypes of rapid cell expansion during flower opening and cell shrinkage at flower closure stage.

CONCLUSIONS

Collectively, our data demonstrate a central regulatory role of auxin in floral movement rhythm and provide a global understanding of flower action in waterlily, which could be a conserved feature of angiosperms.

ZEITLUPE in the Roots of Wild Tobacco Regulates Jasmonate-Mediated Nicotine Biosynthesis and Resistance to a Generalist Herbivore

The jasmonate (JA) phytohormone signaling system is an important mediator of plant defense against herbivores. Plants deficient in JA signaling are more susceptible to herbivory as a result of deficiencies in defensive trait expression. Recent studies have implicated the circadian clock in regulating JA-mediated defenses, but the molecular mechanisms linking the clock to JA signaling are unclear. Here, we report that wild tobacco (Nicotiana attenuata) plants rendered deficient in the clock component ZEITLUPE (ZTL) by RNA interference have attenuated resistance to the generalist herbivore Spodoptera littoralis This effect can be attributed in part to reduced concentrations of nicotine, an abundant JA-regulated toxin produced in N. attenuata roots and transported to shoots. RNA interference targeting ZTL dramatically affects the root circadian clock and reduces the expression of nicotine biosynthetic genes. Protein-protein interaction experiments demonstrate that ZTL regulates JA signaling by directly interacting with JASMONATE ZIM domain (JAZ) proteins in a CORONATINE-INSENSITIVE1- and jasmonoyl-isoleucine conjugate-independent manner, thereby regulating a JAZ-MYC2 module that is required for nicotine biosynthesis. Our study reveals new functions for ZTL and proposes a mechanism by which a clock component directly influences JA signaling to regulate plant defense against herbivory.

Time is honey: circadian clocks of bees and flowers and how their interactions may influence ecological communities

The interactions between flowering plants and insect pollinators shape ecological communities and provide one of the best examples of coevolution. Although these interactions have received much attention in both ecology and evolution, their temporal aspects are little explored. Here we review studies on the circadian organization of pollination-related traits in bees and flowers. Research, mostly with the honeybee, Apis mellifera, has implicated the circadian clock in key aspects of their foraging for flower rewards. These include anticipation, timing of visits to flowers at specified locations and time-compensated sun-compass orientation. Floral rhythms in traits such as petal opening, scent release and reward availability also show robust daily rhythms. However, in only few studies was it possible to adequately determine whether these oscillations are driven by external time givers such as light and temperature cycles, or endogenous circadian clocks. The interplay between the timing of flower and pollinator rhythms may be ecologically significant. Circadian regulation of pollination-related traits in only few species may influence the entire pollination network and thus affect community structure and local biodiversity. We speculate that these intricate chronobiological interactions may be vulnerable to anthropogenic effects such as the introduction of alien invasive species, pesticides or environmental pollutants.This article is part of the themed issue 'Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'.

Circadian clocks of both plants and pollinators influence flower seeking behavior of the pollinator hawkmoth Manduca sexta

Most plant-pollinator interactions occur during specific periods during the day. To facilitate these interactions, many flowers are known to display their attractive qualities, such as scent emission and petal opening, in a daily rhythmic fashion. However, less is known about how the internal timing mechanisms (the circadian clocks) of plants and animals influence their daily interactions. We examine the role of the circadian clock in modulating the interaction between Petunia and one of its pollinators, the hawkmoth Manduca sexta. We find that desynchronization of the Petunia circadian clock affects moth visitation preference for Petunia flowers. Similarly, moths with circadian time aligned to plants show stronger flower-foraging activities than moths that lack this alignment. Moth locomotor activity is circadian clock-regulated, although it is also strongly repressed by light. Moths show a time-dependent burst increase in flight activity during subjective night. In addition, moth antennal responsiveness to the floral scent compounds exhibits a 24-hour rhythm in both continuous light and dark conditions. This study highlights the importance of the circadian clocks in both plants and animals as a crucial factor in initiating specialized plant-pollinator relationships.

Soybean MADS-box gene GmAGL1 promotes flowering via the photoperiod pathway

BACKGROUND

The MADS-box transcription factors are an ancient family of genes that regulate numerous physiological and biochemical processes in plants and facilitate the development of floral organs. However, the functions of most of these transcription factors in soybean remain unknown.

RESULTS

In this work, a MADS-box gene, GmAGL1, was overexpressed in soybean. Phenotypic analysis showed that GmAGL1 overexpression not only resulted in early maturation but also promoted flowering and affected petal development. Furthermore, the GmAGL1 was much more effective at promoting flowering under long-day conditions than under short-day conditions. Transcriptome sequencing analysis showed that before flowering, the photoperiod pathway photoreceptor CRY2 and several circadian rhythm genes, such as SPA1, were significantly down-regulated, while some other flowering-promoting circadian genes, such as GI and LHY, and downstream genes related to flower development, such as FT, LEAFY, SEP1, SEP3, FUL, and AP1, were up-regulated compared with the control. Other genes related to the flowering pathway were not noticeably affected.

CONCLUSIONS

The findings reported herein indicate that GmAGL1 may promote flowering mainly through the photoperiod pathway. Interestingly, while overexpression of GmAGL1 promoted plant maturity, no reduction in seed production or oil and protein contents was observed.

Regulation of the Rhythmic Emission of Plant Volatiles by the Circadian Clock

Like other organisms, plants have endogenous biological clocks that enable them to organize their metabolic, physiological, and developmental processes. The representative biological clock is the circadian system that regulates daily (24-h) rhythms. Circadian-regulated changes in growth have been observed in numerous plants. Evidence from many recent studies indicates that the circadian clock regulates a multitude of factors that affect plant metabolites, especially emitted volatiles that have important ecological functions. Here, we review recent progress in research on plant volatiles showing rhythmic emission under the regulation of the circadian clock, and on how the circadian clock controls the rhythmic emission of plant volatiles. We also discuss the potential impact of other factors on the circadian rhythmic emission of plant volatiles.