Constructing a 3D Bi2WO6/ZnIn2S4 direct Z-scheme heterostructure for improved photocatalytic CO2 reduction performance.

Developing efficient heterojunction photocatalysts with enhanced charge transfer and reduced recombination rates of photogenerated carriers is crucial for harnessing solar energy in the photocatalytic CO2 reduction into renewable fuels. This study employed electrostatic self-assembly techniques to construct a 3D Bi2WO6/ZnIn2S4 direct Z-scheme heterojunctions. The unique 3D structure provided abundant active sites and facilitated CO2 adsorption. Moreover, the optimized Bi2WO6/ZnIn2S4 composite demonstrated an impressive CH4 yield of 19.54 µmol g-1 under 4 h of simulated sunlight irradiation, which was about 8.73 and 16.30-fold higher than pure ZnIn2S4 and Bi2WO6. The observed enhancements in photocatalytic performance are attributed to forming a direct Z-scheme heterojunction, which effectively promotes charge transport and migration. This research introduces a novel strategy for constructing photocatalysts through the synergistic effect of morphological interface modifications.

The apocarotenoid ß-ionone regulates the transcriptome of Arabidopsis thaliana and increases its resistance against Botrytis cinerea.

Carotenoids are isoprenoid pigments indispensable for photosynthesis. Moreover, they are the precursor of apocarotenoids, which include the phytohormones abscisic acid (ABA) and strigolactones (SLs) as well as retrograde signaling molecules and growth regulators, such as ß-cyclocitral and zaxinone. Here, we show that the application of the volatile apocarotenoid ß-ionone (ß-I) to Arabidopsis plants at micromolar concentrations caused a global reprogramming of gene expression, affecting thousands of transcripts involved in stress tolerance, growth, hormone metabolism, pathogen defense, and photosynthesis. This transcriptional reprogramming changes, along with induced changes in the level of the phytohormones ABA, jasmonic acid, and salicylic acid, led to enhanced Arabidopsis resistance to the widespread necrotrophic fungus Botrytis cinerea (B.c.) that causes the gray mold disease in many crop species and spoilage of harvested fruits. Pre-treatment of tobacco and tomato plants with ß-I followed by inoculation with B.c. confirmed the effect of ß-I in increasing the resistance to this pathogen in crop plants. Moreover, we observed reduced susceptibility to B.c. in fruits of transgenic tomato plants overexpressing LYCOPENE ß-CYCLASE, which contains elevated levels of endogenous ß-I, providing a further evidence for its effect on B.c. infestation. Our work unraveled ß-I as a further carotenoid-derived regulatory metabolite and indicates the possibility of establishing this natural volatile as an environmentally friendly bio-fungicide to control B.c.

A carbon-nitrogen negative feedback loop underlies the repeated evolution of cnidarian-Symbiodiniaceae symbioses.

Symbiotic associations with Symbiodiniaceae have evolved independently across a diverse range of cnidarian taxa including reef-building corals, sea anemones, and jellyfish, yet the molecular mechanisms underlying their regulation and repeated evolution are still elusive. Here, we show that despite their independent evolution, cnidarian hosts use the same carbon-nitrogen negative feedback loop to control symbiont proliferation. Symbiont-derived photosynthates are used to assimilate nitrogenous waste via glutamine synthetase-glutamate synthase-mediated amino acid biosynthesis in a carbon-dependent manner, which regulates the availability of nitrogen to the symbionts. Using nutrient supplementation experiments, we show that the provision of additional carbohydrates significantly reduces symbiont density while ammonium promotes symbiont proliferation. High-resolution metabolic analysis confirmed that all hosts co-incorporated glucose-derived 13C and ammonium-derived 15N via glutamine synthetase-glutamate synthase-mediated amino acid biosynthesis. Our results reveal a general carbon-nitrogen negative feedback loop underlying these symbioses and provide a parsimonious explanation for their repeated evolution.

Information-Driven Integrated Healthcare: An Analysis of the Cooperation Strategy of County Medical Community Based on Multi-Subject Simulation.

The fragmentation and uneven quality of primary medical resources in China call for a deepening of integrated healthcare reform. China is promoting its county medical community (CMC) reform on a large scale in county-level administrative regions to promote the integration of local primary healthcare systems through information technology, which is consistent with the current trend of the digital governance era. Considering that the construction of a county medical community involves collaborative relationships between multi-level subjects, the evolutionary game theory was adopted in this study to construct a game model between the lead hospital of a CMC and primary healthcare institutions, and then the incentives of government department support were introduced to analyze the behavioral evolution of these three subjects. Taking into account the uncertainty of the real-life environment and information transformation, white Gaussian noise was introduced as a random disturbance term, and a numerical simulation was performed. In the two-subject model we focus on four parameters: information and management authority ceded by the primary healthcare institutions, integration coefficient of CMC information construction, intensity factor of information integration in the CMC, and medical resources delivered by the lead hospital. In the three-subject model we focus on three parameters: information and portion of authority ceded by the primary healthcare institutions and government departments, policy effect coefficient of CMC construction, and intensity of government departments' support for CMC construction. The simulation results show that there is a positive incentive for the concession of management power and information from the primary healthcare institutions to the lead hospital, but further determination of empowerment boundaries is needed. The lead hospital can improve the balance of medical resources in the county through the downward transfer of medical resources, but long-term resource delivery may inhibit the enthusiasm of the lead hospital. An improvement in the information integration intensity of the CMC can promote the efficient flow of information and knowledge and enhance the organizational closeness of the county medical community. At the same time, the integration of CMC information construction reduces the cost of collaboration among medical community members and streamlines and consolidates business modules, which can promote more efficient use of medical resources. The government departments' policies and funds provide obvious incentives to the lead hospital and primary healthcare institutions, but there is a need to explore appropriate financial payment ratios to balance the government's financial pressure.

The Arabidopsis D27-LIKE1 is a cis/cis/trans-ß-carotene isomerase that contributes to Strigolactone biosynthesis and negatively impacts ABA level.

The enzyme DWARF27 (D27) catalyzes the reversible isomerization of all-trans- into 9-cis-ß-carotene, initiating strigolactone (SL) biosynthesis. Genomes of higher plants encode two D27-homologs, D27-like1 and -like2, with unknown functions. Here, we investigated the enzymatic activity and biological function of the Arabidopsis D27-like1. In vitro enzymatic assays and expression in Synechocystis sp. PCC6803 revealed an unreported 13-cis/15-cis/9-cis- and a 9-cis/all-trans-ß-carotene isomerization. Although disruption of AtD27-like1 did not cause SL deficiency phenotypes, overexpression of AtD27-like1 in the d27 mutant restored the more-branching phenotype, indicating a contribution of AtD27-like1 to SL biosynthesis. Accordingly, generated d27 d27like1 double mutants showed a more pronounced branching phenotype compared to d27. The contribution of AtD27-like1 to SL biosynthesis is likely a result of its formation of 9-cis-ß-carotene that was present at higher levels in AtD27-like1 overexpressing lines. By contrast, AtD27-like1 expression correlated negatively with the content of 9-cis-violaxanthin, a precursor of ABA, in shoots. Consistently, ABA levels were higher in shoots and also in dry seeds of the d27like1 and d27 d27like1 mutants. Transgenic lines expressing GUS driven by the AtD27LIKE1 promoter and transcript analysis of hormone-treated Arabidopsis seedlings revealed that AtD27LIKE1 is expressed in different tissues and affects ABA and auxin. Taken together, our work reports a cis/cis-ß-carotene isomerase that affects the content of both cis-carotenoid-derived plant hormones, ABA and SLs.

Gardenia carotenoid cleavage dioxygenase 4a is an efficient tool for biotechnological production of crocins in green and non-green plant tissues.

Crocins are beneficial antioxidants and potential chemotherapeutics that give raise, together with picrocrocin, to the colour and taste of saffron, the most expensive spice, respectively. Crocins are formed from crocetin dialdehyde that is produced in Crocus sativus from zeaxanthin by the carotenoid cleavage dioxygenase 2L (CsCCD2L), while GjCCD4a from Gardenia jasminoides, another major source of crocins, converted different carotenoids, including zeaxanthin, into crocetin dialdehyde in bacterio. To establish a biotechnological platform for sustainable production of crocins, we investigated the enzymatic activity of GjCCD4a, in comparison with CsCCD2L, in citrus callus engineered by Agrobacterium-mediated supertransformation of multi genes and in transiently transformed Nicotiana benthamiana leaves. We demonstrate that co-expression of GjCCD4a with phytoene synthase and ß-carotene hydroxylase genes is an optimal combination for heterologous production of crocetin, crocins and picrocrocin in citrus callus. By profiling apocarotenoids and using in vitro assays, we show that GjCCD4a cleaved ß-carotene, in planta, and produced crocetin dialdehyde via C30 ß-apocarotenoid intermediate. GjCCD4a also cleaved C27 ß-apocarotenoids, providing a new route for C17 -dialdehyde biosynthesis. Callus lines overexpressing GjCCD4a contained higher number of plastoglobuli in chromoplast-like plastids and increased contents in phytoene, C17:0 fatty acid (FA), and C18:1 cis-9 and C22:0 FA esters. GjCCD4a showed a wider substrate specificity and higher efficiency in Nicotiana leaves, leading to the accumulation of up to 1.6 mg/g dry weight crocins. In summary, we established a system for investigating CCD enzymatic activity in planta and an efficient biotechnological platform for crocins production in green and non-green crop tissues/organs.

Screening for apocarotenoid plant growth regulators in Arabidopsis.

Apocarotenoids are bioactive metabolites found in animals, fungi and plants. Several carotenoid-derived compounds, apocarotenoids, were recently identified as new growth regulators in different plant species. Here, we introduce basic chemical screening methods, using a model plant, Arabidopsis thaliana, to elucidate the function of bioactive apocarotenoids in determining plant phenotypic traits. These short guidelines include essential practices, such as selecting the plant growth conditions and the type of treatment, as well as phenotyping methodologies for the initial screening of novel apocarotenoid plant growth regulators.

Ultra-high performance liquid chromatography-mass spectrometry analysis of plant apocarotenoids.

Apocarotenoids (APOs) are a class of carotenoid oxidation products with high structural and functional diversity. Apart from serving as precursors of phytohormones, fungal pheromones and vitamin A, several APOs act as signaling molecules involved in stress response and growth as regulators in plants. To comprehensively profile plant APOs, we established an improved ultra-high performance liquid chromatography-hybrid quadrupole-Orbitrap mass spectrometer (UHPLC-Q-Orbitrap MS) analytical platform. The improved APO analytical platform consists of an optimized sequential APO sample preparation and multiple UHPLC-MS detection methods and was successfully used to identify and quantify multiple subclasses of APOs from tomato fruits. By integrating ultrasound-assisted extraction, solid phase extraction, and chemical derivatization, the improved sequential APOs sample preparation facilitates the simultaneous preparation of different subclasses of APOs from plant materials. In addition, multiple UHPLC-MS detection methods enables high throughput analysis of APOs. Application of this analytical strategy can make important contributions to understanding the function of these compounds and significantly facilitate the elucidation of plant APO metabolism.

Characterizing cytochrome P450 enzymes involved in plant apocarotenoid metabolism by using an engineered yeast system.

Cytochrome P450 enzymes (CYPs) are involved in metabolic steps that provide structural diversity during the biosynthesis of carotenoids and their oxidative cleavage products called apocarotenoids. Recent studies on bioactive apocarotenoids in plants revealed the necessity of performing further research to uncover the function of novel CYP enzymes that might be involved in apocarotenoid metabolism. We describe a series of in-vitro methods to characterize plant CYPs that metabolize apocarotenoids, using a specific Saccharomyces cerevisiae strain, WAT11, engineered to express a CYP redox partner, Arabidopsis thaliana NADPH-P450 reductase 1 (ATR1). This chapter provides protocols for construction and transformation of plasmids that express CYPs in yeast, isolation of yeast microsomes, and in-vitro enzymatic assays to validate the final metabolic products using LC-MS.

High-energy-level metabolism and transport occur at the transition from closed to open flowers.

During the maturation phase of flower development, the onset of anthesis visibly marks the transition from buds to open flowers, during which petals stretch out, nectar secretion commences, and pollination occurs. Analysis of the metabolic changes occurring during this developmental transition has primarily focused on specific classes of metabolites, such as pigments and scent emission, and far less on the whole network of primary and secondary metabolites. To investigate the metabolic changes occurring at anthesis, we performed multi-platform metabolomics alongside RNA sequencing in individual florets harvested from the main inflorescence of Arabidopsis (Arabidopsis thaliana) ecotype Col-0. To trace metabolic fluxes at the level of the whole inflorescence and individual florets, we further integrated these studies with radiolabeled experiments. These extensive analyses revealed high-energy-level metabolism and transport of carbohydrates and amino acids, supporting intense metabolic rearrangements occurring at the time of this floral transition. These comprehensive data are discussed in the context of our current understanding of the metabolic shifts underlying flower opening. We envision that this analysis will facilitate the introgression of floral metabolic traits promoting pollination in crop species for which a comprehensive knowledge of flower metabolism is still limited.

Ultrahigh-Performance Liquid Chromatography-Mass Spectrometry Analysis of Carotenoid-Derived Hormones and Apocarotenoids in Plants.

Carotenoid oxidative cleavage products, apocarotenoids (APOs), are a class of important plant secondary metabolites, which include phytohormones abscisic acid (ABA) and strigolactones (SLs), and growth regulators and signaling molecules such as ß-cyclocitral, zaxinone, anchorene, ß-apo-11-carotenoids, and retinal. Qualitative and quantitative analysis of these bioactive compounds is crucial for understanding their metabolism and may also enable discovering further regulatory APOs. The state-of-the-art mass spectrometry (MS) technology has advanced the detection of plant APOs; however, it is still challenging to perform an accurate analysis of the low-level phytohormones ABA and SL and the structurally diverse APOs from complex plant matrices. Here, we describe ultrahigh-performance liquid chromatography-MS (UHPLC-MS) methods to determine carotenoid-derived hormones and APOs from plants by integrating ultrasound-assisted extraction and solid-phase extraction. These assays enable an accurate quantification of carotenoid-derived hormones and APOs from plant tissues by using an UHPLC hybrid quadrupole-Orbitrap mass spectrometer. © 2022 Wiley Periodicals LLC. Basic Protocol 1: UHPLC-MS analysis of APOs from rice roots Support Protocol: Preparation of dried plant root powder Basic Protocol 2: UHPLC-MS analysis of SLs from rice roots Basic Protocol 3: UHPLC-MS analysis of ABA from rice roots.

A manipulation of carotenoid metabolism influence biomass partitioning and fitness in tomato.

Improving yield, nutritional value and tolerance to abiotic stress are major targets of current breeding and biotechnological approaches that aim at increasing crop production and ensuring food security. Metabolic engineering of carotenoids, the precursor of vitamin-A and plant hormones that regulate plant growth and response to adverse growth conditions, has been mainly focusing on provitamin A biofortification or the production of high-value carotenoids. Here, we show that the introduction of a single gene of the carotenoid biosynthetic pathway in different tomato cultivars induced profound metabolic alterations in carotenoid, apocarotenoid and phytohormones pathways. Alterations in isoprenoid- (abscisic acid, gibberellins, cytokinins) and non-isoprenoid (auxin and jasmonic acid) derived hormones together with enhanced xanthophyll content influenced biomass partitioning and abiotic stress tolerance (high light, salt, and drought), and it caused an up to 77% fruit yield increase and enhanced fruit's provitamin A content. In addition, metabolic and hormonal changes led to accumulation of key primary metabolites (e.g. osmoprotectants and antiaging agents) contributing with enhanced abiotic stress tolerance and fruit shelf life. Our findings pave the way for developing a new generation of crops that combine high productivity and increased nutritional value with the capability to cope with climate change-related environmental challenges.

An alternative, zeaxanthin epoxidase-independent abscisic acid biosynthetic pathway in plants.

Abscisic acid (ABA) is an important carotenoid-derived phytohormone that plays essential roles in plant response to biotic and abiotic stresses as well as in various physiological and developmental processes. In Arabidopsis, ABA biosynthesis starts with the epoxidation of zeaxanthin by the ABA DEFICIENT 1 (ABA1) enzyme, leading to epoxycarotenoids; e.g., violaxanthin. The oxidative cleavage of 9-cis-epoxycarotenoids, a key regulatory step catalyzed by 9-CIS-EPOXYCAROTENOID DIOXYGENASE, forms xanthoxin, which is converted in further reactions mediated by ABA DEFICIENT 2 (ABA2), ABA DEFICIENT 3 (ABA3), and ABSCISIC ALDEHYDE OXIDASE 3 (AAO3) into ABA. By combining genetic and biochemical approaches, we unravel here an ABA1-independent ABA biosynthetic pathway starting upstream of zeaxanthin. We identified the carotenoid cleavage products (i.e., apocarotenoids, ß-apo-11-carotenal, 9-cis-ß-apo-11-carotenal, 3-OH-ß-apo-11-carotenal, and 9-cis-3-OH-ß-apo-11-carotenal) as intermediates of this ABA1-independent ABA biosynthetic pathway. Using labeled compounds, we showed that ß-apo-11-carotenal, 9-cis-ß-apo-11-carotenal, and 3-OH-ß-apo-11-carotenal are successively converted into 9-cis-3-OH-ß-apo-11-carotenal, xanthoxin, and finally into ABA in both Arabidopsis and rice. When applied to Arabidopsis, these ß-apo-11-carotenoids exert ABA biological functions, such as maintaining seed dormancy and inducing the expression of ABA-responsive genes. Moreover, the transcriptomic analysis revealed a high overlap of differentially expressed genes regulated by ß-apo-11-carotenoids and ABA, suggesting that ß-apo-11-carotenoids exert ABA-independent regulatory activities. Taken together, our study identifies a biological function for the common plant metabolites, ß-apo-11-carotenoids, extends our knowledge about ABA biosynthesis, and provides new insights into plant apocarotenoid metabolic networks.

Iso-anchorene is an endogenous metabolite that inhibits primary root growth in Arabidopsis.

Carotenoid-derived regulatory metabolites and hormones are generally known to arise through the oxidative cleavage of a single double bond in the carotenoid backbone, which yields mono-carbonyl products called apocarotenoids. However, the extended conjugated double bond system of these pigments predestines them also to repeated cleavage forming dialdehyde products, diapocarotenoids, which have been less investigated due to their instability and low abundance. Recently, we reported on the short diapocarotenoid anchorene as an endogenous Arabidopsis metabolite and specific signaling molecule that promotes anchor root formation. In this work, we investigated the biological activity of a synthetic isomer of anchorene, iso-anchorene, which can be derived from repeated carotenoid cleavage. We show that iso-anchorene is a growth inhibitor that specifically inhibits primary root growth by reducing cell division rates in the root apical meristem. Using auxin efflux transporter marker lines, we also show that the effect of iso-anchorene on primary root growth involves the modulation of auxin homeostasis. Moreover, by using liquid chromatography-mass spectrometry analysis, we demonstrate that iso-anchorene is a natural Arabidopsis metabolite. Chemical inhibition of carotenoid biosynthesis led to a significant decrease in the iso-anchorene level, indicating that it originates from this metabolic pathway. Taken together, our results reveal a novel carotenoid-derived regulatory metabolite with a specific biological function that affects root growth, manifesting the biological importance of diapocarotenoids.

LC-MS-Based Profiling Provides New Insights into Apocarotenoid Biosynthesis and Modifications in Citrus Fruits.

Apocarotenoids contribute to fruit color and aroma, which are critical quality and marketability attributes. Previously, we reported that the red peels of citrus fruits, which are characterized by higher expression levels of a carotenoid cleavage dioxygenase 4b (CitCCD4b) gene, accumulate higher levels of ß-citraurin and ß-citraurinene than yellow peels. Here, we identified and quantified 12 apocarotenoids, either volatile or nonvolatile, in citrus peel using liquid chromatography-mass spectrometry (LC-MS). Our results show that red peels contain also dramatically higher amounts of ß-apo-8'-carotenal, crocetin dialdehyde known from saffron, ß-citraurol, ß-cyclocitral, and 3-OH-ß-cyclocitral and up to about 17-fold higher levels of 3-OH-ß-cyclocitral glucoside (picrocrocin isomer). The content of these apocarotenoids was also significantly increased in different CitCCD4b-overexpressing transgenic callus lines, compared with corresponding controls. Transient expression of CitCCD4b in Nicotiana benthamiana leaves resulted in a striking increase in the 3-OH-ß-cyclocitral level and the accumulation of picrocrocin. Thus, our work reinforces the specific function of CitCCD4b in producing C10 apocarotenoid volatiles and C30 pigments in citrus peel and uncovers its involvement in the biosynthesis of picrocrocin, C20 dialdehyde, and C30 alcohol apocarotenoids, suggesting the potential of this enzyme in metabolic engineering of apocarotenoids and their derivatives.

Novel Fatty Acid in Cordyceps Suppresses Influenza A (H1N1) Virus-Induced Proinflammatory Response Through Regulating Innate Signaling Pathways.

Influenza virus (IV) infections usually cause acute lung injury characterized by exaggerated proinflammatory responses. The paucity of therapeutic strategies that target host immune response to attenuate lung injury poses a substantial challenge in management of IV infections. In this study, we chemically synthesized a novel fatty acid (2Z,4E)-deca-2,4-dienoic acid (DDEA) identified from Chinese Cordyceps by using UHPLC-Q-TOF-MS techniques. The DDEA did not inhibit H1N1 virus replication but attenuated proinflammatory responses by reducing mRNA and protein levels of TNF-α, IFN-α, IFN-ß, IL-6, CXCL-8/IL-8, CCL-2/MCP-1, CXCL-10/IP-10, CCL-3/MIP-1α, and CCL-4/MIP-1ß in A549 cells and U937-derived macrophages. The anti-inflammatory effect occurred through downregulations of TLR-3-, RIG-I-, and type I IFN-activated innate immune signaling pathways. Altogether, our results indicate that DDEA may potentially be used as an anti-inflammatory therapy for the treatment of IV infections.

Lycopene ß-cyclase expression influences plant physiology, development, and metabolism in tobacco plants.

Carotenoids are important isoprenoids produced in the plastids of photosynthetic organisms that play key roles in photoprotection and antioxidative processes. ß-Carotene is generated from lycopene by lycopene ß-cyclase (LCYB). Previously, we demonstrated that the introduction of the Daucus carota (carrot) DcLCYB1 gene into tobacco (cv. Xanthi) resulted in increased levels of abscisic acid (ABA) and especially gibberellins (GAs), resulting in increased plant yield. In order to understand this phenomenon prior to exporting this genetic strategy to crops, we generated tobacco (Nicotiana tabacum cv. Petit Havana) mutants that exhibited a wide range of LCYB expression. Transplastomic plants expressing DcLCYB1 at high levels showed a wild-type-like growth, even though their pigment content was increased and their leaf GA1 content was reduced. RNA interference (RNAi) NtLCYB lines showed different reductions in NtLCYB transcript abundance, correlating with reduced pigment content and plant variegation. Photosynthesis (leaf absorptance, Fv/Fm, and light-saturated capacity of linear electron transport) and plant growth were impaired. Remarkably, drastic changes in phytohormone content also occurred in the RNAi lines. However, external application of phytohormones was not sufficient to rescue these phenotypes, suggesting that altered photosynthetic efficiency might be another important factor explaining their reduced biomass. These results show that LCYB expression influences plant biomass by different mechanisms and suggests thresholds for LCYB expression levels that might be beneficial or detrimental for plant growth.

Plant apocarotenoids: from retrograde signaling to interspecific communication.

Carotenoids are isoprenoid compounds synthesized by all photosynthetic and some non-photosynthetic organisms. They are essential for photosynthesis and contribute to many other aspects of a plant's life. The oxidative breakdown of carotenoids gives rise to the formation of a diverse family of essential metabolites called apocarotenoids. This metabolic process either takes place spontaneously through reactive oxygen species or is catalyzed by enzymes generally belonging to the CAROTENOID CLEAVAGE DIOXYGENASE family. Apocarotenoids include the phytohormones abscisic acid and strigolactones (SLs), signaling molecules and growth regulators. Abscisic acid and SLs are vital in regulating plant growth, development and stress response. SLs are also an essential component in plants' rhizospheric communication with symbionts and parasites. Other apocarotenoid small molecules, such as blumenols, mycorradicins, zaxinone, anchorene, ß-cyclocitral, ß-cyclogeranic acid, ß-ionone and loliolide, are involved in plant growth and development, and/or contribute to different processes, including arbuscular mycorrhiza symbiosis, abiotic stress response, plant-plant and plant-herbivore interactions and plastid retrograde signaling. There are also indications for the presence of structurally unidentified linear cis-carotene-derived apocarotenoids, which are presumed to modulate plastid biogenesis and leaf morphology, among other developmental processes. Here, we provide an overview on the biology of old, recently discovered and supposed plant apocarotenoid signaling molecules, describing their biosynthesis, developmental and physiological functions, and role as a messenger in plant communication.