Nucleotides, micro- and macro-nutrients, limonoids, flavonoids, and hydroxycinnamates composition in the phloem sap of sweet orange

Four novel Cit7GlcTs functional in flavonoid 7-O-glucoside biosynthesis are vital to flavonoid biosynthesis shunting in citrus

Citrus fruits have abundant flavonoid glycosides (FGs), an important class of natural functional and flavor components. However, there have been few reports about the modification of UDP-glycosyltransferases (UGTs) on flavonoids in citrus. Notably, in flavonoid biosynthesis, 7-O-glucosylation is the initial and essential step of glycosylation prior to the synthesis of flavanone disaccharides, the most abundant and iconic FGs in citrus fruits. Here, based on the accumulation of FGs observed at the very early fruit development stage of two pummelo varieties, we screened six novel flavonoid 7-O-glucosyltransferase genes (7GlcTs) via transcriptomic analysis and then characterized them in vitro. The results revealed that four Cg7GlcTs possess wide catalytic activities towards various flavonoid substrates, with CgUGT89AK1 exhibiting the highest catalytic efficiency. Transient overexpression of CgUGT90A31 and CgUGT89AK1 led to increases in FG synthesis in pummelo leaves. Interestingly, these two genes had conserved sequences and consistent functions across different germplasms. Moreover, CitUGT89AK1 was found to play a role in the response of citrus to Huanglongbing infection by promoting FG production. The findings improve our understanding of flavonoid 7-O-glucosylation by identifying the key genes, and may help improve the benefits of flavonoid biosynthesis for plants and humans in the future.

Therapeutic effectiveness of sinensetin against cancer and other human complications: A review of biological potential and pharmacological activities

BACKGROUND

Plant and their active phytoproducts have been used in modern medicine and playing an important role in the health sectors since a very early age. Human beings need a considerable amount of these plant-based phytochemicals for their health. The flavonoidal class phytochemical is an important class of natural products in modern healthcare because of their different pharmacological activities and health benefits. Flavonoidal class phytochemicals have been used to treat diabetes and related secondary complications in humans. Flavonoids have anti-apoptotic, anti-hyperlipidemic, anti-inflammatory, and anti-oxidant potential in the health sectors. Sinensetin, also called 3',4',5,6,7-pentametoksiflavon is a colorless compound with a molecular weight 372.37g/mol and is found to be present in the Orthosiphon stamineus.

METHODS

In the present investigation, we aim to collect scientific information on sinensetin and analyze it for its biological potential and therapeutic benefits against various types of disorders and complications. Medicinal importance and pharmacological activities data have been collected and analyzed in the present work for sinensetin through literature data analysis of different research works. Google Science Direct, PubMed, Scopus, and Google Scholar were mainly searched to collect the scientific information in the present work. The present work analyzed sinensetin's biological potential, pharmacological activities, and analytical aspects.

RESULTS

Literature data analysis of different scientific research works revealed the biological potential of phytochemicals in medicine, including flavonoids. Sinensetin has anti-tumor, anti-inflammatory, anti-oxidant, anti-diabetic, and antibacterial activities through their testing in different in vitro and in vivo models. Sinensetin has physiological functions, including anti-oxidant, anti-inflammation, and anti-cancer potential in medicine. Scientific data analysis signified the biological importance of sinensetin against tumors, gastric cancer, colorectal cancer, breast cancer, diabetes, influenza H1N1 infection, obesity, inflammation, colitis, brain disorders, and microbial infections. Further biological potential of sinensetin on enzymes and angiogenesis has been analyzed in the present work. Sinensetin was isolated through different analytical and extraction techniques, including chromatographic techniques.

CONCLUSION

Literature data analysis signified sinensetin's biological potential and pharmacological activities in medicine.

Citrus Huanglongbing detection and semi-quantification of the carbohydrate concentration based on micro-FTIR spectroscopy

Citrus Huanglongbing (HLB) is nowadays one of the most fatal citrus diseases worldwide. Once the citrus tree is infected by the HLB disease, the biochemistry of the phloem region in midribs would change. In order to investigate the carbohydrate changes in phloem region of citrus midrib, the semi-quantification models were established to predict the carbohydrate concentration in it based on Fourier transform infrared microscopy (micro-FTIR) spectroscopy coupled with chemometrics. Healthy, asymptomatic-HLB, symptomatic-HLB, and nutrient-deficient citrus midribs were collected in this study. The results showed that the intensity of the characteristic peak varied with the carbohydrate (starch and soluble sugar) concentration in citrus midrib, especially at the fingerprint regions of 1175-900 cm^-1, 1500-1175 cm^-1, and 1800-1500 cm^-1. Furthermore, semi-quantitative prediction models of starch and soluble sugar were established using the full micro-FTIR spectra and selected characteristic wavebands. The least squares support vector machine regression (LS-SVR) model combined with the random frog (RF) algorithm achieved the best prediction result with the determination coefficient of prediction ([Formula: see text]) of 0.85, the root mean square error of prediction (RMSEP) of 0.36%, residual predictive deviation (RPD) of 2.54, and [Formula: see text] of 0.87, RMSEP of 0.37%, RPD of 2.76, for starch and soluble sugar concentration prediction, respectively. In addition, multi-layer perceptron (MLP) classification models were established to identify HLB disease, achieving the overall classification accuracy of 94% and 87%, based on the full-range spectra and the optimal wavenumbers selected by the random frog (RF) algorithm, respectively. The results demonstrated that micro-FTIR spectroscopy can be a valuable tool for the prediction of carbohydrate concentration in citrus midribs and the detection of HLB disease, which would provide useful guidelines to detect citrus HLB disease.

Bioprospecting Microbiome for Soil and Plant Health Management Amidst Huanglongbing Threat in Citrus: A Review

Microorganisms have dynamic and complex interactions with their hosts. Diverse microbial communities residing near, on, and within the plants, called phytobiome, are an essential part of plant health and productivity. Exploiting citrus-associated microbiomes represents a scientific approach toward sustained and environment-friendly module of citrus production, though periodically exposed to several threats, with Huanglongbing (HLB) predominantly being most influential. Exploring the composition and function of the citrus microbiome, and possible microbial redesigning under HLB disease pressure has sparked renewed interest in recent times. A concise account of various achievements in understanding the citrus-associated microbiome, in various niche environments viz., rhizosphere, phyllosphere, endosphere, and core microbiota alongside their functional attributes has been thoroughly reviewed and presented. Efforts were also made to analyze the actual role of the citrus microbiome in soil fertility and resilience, interaction with and suppression of invading pathogens along with native microbial communities and their consequences thereupon. Despite the desired potential of the citrus microbiota to counter different pathogenic diseases, utilizing the citrus microbiome for beneficial applications at the field level is yet to be translated as a commercial product. We anticipate that advancement in multiomics technologies, high-throughput sequencing and culturing, genome editing tools, artificial intelligence, and microbial consortia will provide some exciting avenues for citrus microbiome research and microbial manipulation to improve the health and productivity of citrus plants.

Extraction of cucumber phloem sap based on the capillary-air pressure principle

Changes in the substances in phloem sap can effectively reflect the nutritional status of cucumber plants during their growth. Because of the limitations of the time-consuming and complex operations of existing phloem sap extraction methods, the authors proposed a new extraction method based on the capillary-air pressure principle and designed a new sap sampling device. To examine the feasibility of the new sampling device, sap sampled from the same plant with the new method and the common EDTA method was analyzed by gas-phase mass spectrometry. The data showed that the number of substances in the sap sampled using capillary-air pressure was higher than that observed using the EDTA method. The concentration of substances sampled using capillary-air pressure was much higher than that observed using EDTA.

Sap Analysis: A Powerful Tool for Monitoring Plant Nutrition

Horticultural crop production is moving towards an era of higher nutrient use efficiency since nutrient deficiencies can reduce plant growth, productivity, and quality, and overfertilization can cause environmental pollution. Rapid nutrient concentration diagnostic is essential to minimize the negative effects of Huanglongbing (HLB) or citrus greening in citrus by providing the required nutrients before deficiency symptoms appear, reducing the impact of the disease on crop production. Sap analysis is an additional tool for fine-tuning nutrient applications in citrus. The main objective of this paper is to review the different methodologies and results obtained with sap analysis, considering its potential application in citrus production. Results from other crops show the pros and cons of using this tool. Substantial research has been conducted on vegetables and greenhouse crops, but few studies are available on perennial species such as citrus. Inconsistency in the extraction and analysis methods and the lack of specific sufficiency ranges for citrus open the path for further studies. Along with soil and leaf analyses, sap analysis is a complementary technique that can improve nutrient use efficiency in citrus production. Moreover, sap analysis has the potential to optimize fertilizer application, minimize environmental impacts and improve sustainability.

Metabolomic Analysis Provides New Insight Into Tolerance of Huanglongbing in Citrus

There have been efforts to develop citrus cultivars that are tolerant of Huanglongbing (HLB), a catastrophic phloem-limited disease. Previous studies demonstrated that continuous plant growth with phloem regeneration is one of the major characteristics of HLB tolerance. In this study, the metabolic mechanisms of HLB tolerance in citrus were elucidated using a multiple pathway-targeted metabolomic approach. Comparative analysis of healthy and infected HLB-tolerant and HLB-sensitive mandarin cultivars (Citrus reticulata) revealed differentially expressed metabolic responses among different groups. Pathway enrichment analysis indicated aspartate and glutamate metabolism, purine metabolism, and biosynthesis of plant hormones were upregulated in the tolerant group, except salicylic acid signaling. Catabolic pathways linked to energy-yielding metabolism were also upregulated in the tolerant group. These metabolisms and pathways were interconnected with each other, unveiling a pivotal metabolic network associated with HLB tolerance. In the network, auxins and cytokinins, the plant hormones responsible for plant growth and phloem regeneration, were accumulated. In addition, purine metabolites serving as energy carriers and nitrogen sources of plants were increased. Only salicylic acid-related metabolites for plant defense responses were decreased in the tolerant group. Our findings may evidence the strategy of HLB-tolerant cultivars that sustain plant growth and phloem formation rather than displaying direct plant defense to overcome the disease.

Seasonal changes in temperate woody plant phloem anatomy and physiology: implications for long-distance transport

Seasonal changes in climate are accompanied by shifts in carbon allocation and phenological changes in woody angiosperms, the timing of which can have broad implications for species distributions, interactions and ecosystem processes. During critical transitions from autumn to winter and winter to spring, physiological and anatomical changes within the phloem could impose a physical limit on the ability of woody angiosperms to transport carbon and signals. There is a paucity of the literature that addresses tree (floral or foliar) phenology, seasonal phloem anatomy and seasonal phloem physiology together, so our knowledge of how carbon transport could fluctuate seasonally, especially in temperate climates is limited. We review phloem phenology focussing on how sieve element anatomy and phloem sap flow could affect carbon availability throughout the year with a focus on winter. To investigate whether flow is possible in the winter, we construct a simple model of phloem sap flow and investigate how changes to the sap concentration, pressure gradient and sieve plate pores could influence flow during the winter. Our model suggests that phloem transport in some species could occur year-round, even in winter, but current methods for measuring all the parameters surrounding phloem sap flow make it difficult to test this hypothesis. We highlight outstanding questions that remain about phloem functionality in the winter and emphasize the need for new methods to address gaps in our knowledge about phloem function.

Fruits

Fruits come in a wide variety of colors, shapes, and flavors. This chapter will cover selected fruits that are known to be healthy and highly nutritious. These fruits were chosen due to their common usage and availability. Since it is not possible to cover all health benefits or essential nutrients and important phytochemicals of the fruit composition, this chapter will focus on the key valuable constituents and their potential health effects.

Sieve element biology provides leads for research on phytoplasma lifestyle in plant hosts

Phytoplasmas reside exclusively in sieve tubes, tubular arrays of sieve element-companion cell complexes. Hence, the cell biology of sieve elements may reveal (ultra)structural and functional conditions that are of significance for survival, propagation, colonization, and effector spread of phytoplasmas. Electron microscopic images suggest that sieve elements offer facilities for mobile and stationary stages in phytoplasma movement. Stationary stages may enable phytoplasmas to interact closely with diverse sieve element compartments. The unique, reduced sieve element outfit requires permanent support by companion cells. This notion implies a future focus on the molecular biology of companion cells to understand the sieve element-phytoplasma inter-relationship. Supply of macromolecules by companion cells is channelled via specialized symplasmic connections. Ca2+-mediated gating of symplasmic corridors is decisive for the communication within and beyond the sieve element-companion cell complex and for the dissemination of phytoplasma effectors. Thus, Ca2+ homeostasis, which affects sieve element Ca2+ signatures and induces a range of modifications, is a key issue during phytoplasma infection. The exceptional physical and chemical environment in sieve elements seems an essential, though not the only factor for phytoplasma survival.

Progress and Obstacles in Culturing 'Candidatus Liberibacter asiaticus', the Bacterium Associated with Huanglongbing

In recent decades, 'Candidatus Liberibacter spp.' have emerged as a versatile group of psyllid-vectored plant pathogens and endophytes capable of infecting a wide range of economically important plant hosts. The most notable example is 'Candidatus Liberibacter asiaticus' (CLas) associated with Huanglongbing (HLB) in several major citrus-producing areas of the world. CLas is a phloem-limited α-proteobacterium that is primarily vectored and transmitted among citrus species by the Asian citrus psyllid (ACP) Diaphorina citri. HLB was first detected in North America in Florida (USA) in 2005, following introduction of the ACP to the State in 1998. HLB rapidly spread to all citrus growing regions of Florida within three years, with severe economic consequences to growers and considerable expense to taxpayers of the state and nation. Inability to establish CLas in culture (except transiently) remains a significant scientific challenge toward effective HLB management. Lack of axenic cultures has restricted functional genomic analyses, transfer of CLas to either insect or plant hosts for fulfillment of Koch's postulates, characterization of host-pathogen interactions and effective screening of antibacterial compounds. In the last decade, substantial progress has been made toward CLas culturing: (i) three reports of transient CLas cultures were published, (ii) a new species of Liberibacter was identified and axenically cultured from diseased mountain papaya (Liberibacter crescens strain BT-1), (iii) psyllid hemolymph and citrus phloem sap were biochemically characterized, (iv) CLas phages were identified and lytic genes possibly affecting CLas growth were described, and (v) genomic sequences of 15 CLas strains were made available. In addition, development of L. crescens as a surrogate host for functional analyses of CLas genes, has provided valuable insights into CLas pathogenesis and its physiological dependence on the host cell. In this review we summarize the conclusions from these important studies.

Studying Phloem Loading with EDTA-Facilitated Phloem Exudate Collection and Analysis

Sugars that are produced by photosynthesis in the leaves are transported in the phloem to heterotrophic sink tissues like roots, fruit, or flowers. Since sugars inside the highly specialized cells of the phloem move by bulk flow, it is the loading and unloading of sugars that determines the rates of allocation between organs. Here, a method is described for the relative quantification of sugars that are loaded into the phloem in leaves. It is based on EDTA-facilitated phloem exudate collection and, therefore, requires control experiments to exclude measurement artifacts. It can be applied to a wide range of plant species, including dicots, monocots, and trees.

Sorghum 3-Deoxyanthocyanidin Flavonoids Confer Resistance against Corn Leaf Aphid

In this study we examined the role of sorghum flavonoids in providing resistance against corn leaf aphid (CLA) Rhopalosiphum maidis. In sorghum, accumulation of these flavonoids is regulated by a MYB transcription factor, yellow seed1 (y1). Functional y1 alleles accumulate 3-deoxyflavonoids (3-DFs) and 3-deoxyanthocyanidins (3-DAs) whereas null y1 alleles fail to accumulate these compounds. We found that significantly higher numbers of alate CLA adults colonized null y1 plants as compared to functional y1 plants. Controlled cage experiments and pairwise choice assays demonstrated that apterous aphids preferred to feed and reproduce on null y1 plants. These near-isogenic sorghum lines do not differ in their epicuticular wax content and were also devoid of any leaf trichomes. Significantly higher mortality of CLA was observed on artificial aphid diet supplemented with flavonoids obtained from functional y1 plants as compared to null y1 plants or the relevant controls. Our results demonstrate that the proximate mechanism underlying the deleterious effects on aphids is y1-regulated flavonoids which are important defense compounds against CLA.

FG. Phloem Regeneration Is a Mechanism for Huanglongbing-Tolerance of "Bearss" Lemon and "LB8-9" Sugar Belle® Mandarin

Huanglongbing (HLB) is an extremely destructive and lethal disease of citrus worldwide, presumably caused by phloem-limited bacteria, Candidatus Liberibacter asiaticus (CLas). The widespread invasiveness of the HLB pathogen and lack of natural HLB-resistant citrus cultivars have underscored the need for identifying tolerant citrus genotypes to support the current citrus industry's survival and potentially to lead to future natural HLB resistance. In this study, transverse sections of leaf lamina and midribs were examined with light and epifluorescence microscopy to determine anatomical characteristics that underlie HLB-tolerant mechanisms operating among "Bearss" lemon, "LB8-9" Sugar Belle^® mandarin, and its sibling trees compared with HLB-sensitive "Valencia" sweet orange. The common anatomical aberrations observed in all CLas-infected varieties are as follows: phloem necrosis, hypertrophic phloem parenchyma cells, phloem plugging with abundant callose depositions, phloem collapse with cell wall distortion and thickening, excessive starch accumulation, and sometimes even cambium degeneration. Anatomical distribution of starch accumulation even extended to tracheid elements. Although there were physical, morphological, and pathological similarities in the examined foliage, internal structural preservation in "Bearss" lemon and "LB8-9" Sugar Belle^® mandarin was superior compared with HLB-sensitive "Valencia" sweet orange and siblings of "LB8-9" Sugar Belle^® mandarin. Intriguingly, there was substantial phloem regeneration in the tolerant types that may compensate for the dysfunctional phloem, in comparison with the sensitive selections. The lower levels of phloem disruption, together with greater phloem regeneration, are two key elements that contribute to HLB tolerance in diverse citrus cultivars.

Collection of the phloem sap, pros and cons

Phloem tissue is essential for the translocation of nutrients, water, energy, and signals in plants. In order to study the chemical composition of phloem sap, several methods have been used for its collection including the dipotassium ethylenediamine tetraacetic acid (K₂-EDTA) exudation, incision, and the stylectomy by aphids. Each method has advantages and disadvantages. Unfortunately, there is no ideal method that can be used for all plants or to collect ultrapure phloem sap with no cellular contamination. However, K₂-EDTA exudation is the most used method because it is easy, fast, and results in a high quantity of phloem sap. In woody plants, it is easy to separate the bark. Using the bark which contains the phloem tissue would avoid the contamination with xylem sap when phloem sap is collected. Lately, we developed a simple and a quick method for the collection of the citrus phloem sap depending on the centrifugation of the detached bark tissue. Here, I report the advantages of the centrifugation method over the K₂-EDTA exudation in collecting phloem sap from citrus. To emphasize the purity of collected saps, phloem sap (from bark tissue) and xylem sap (from inner part of stem) were collected using both methods. Using gas chromatography mass spectrometry, the centrifugation method showed less artifact peaks than the K₂-EDTA exudation indicating more pure saps were collected. For instant, less hexoses were detected in phloem sap and the absence of sucrose in xylem sap in centrifugation method than in K₂-EDTA exudation. More importantly, centrifugation method allowed accurate estimation of the concentrations of metabolites. This method could be successfully used for the collection of saps of citrus and other trees until the invention of a more specific method to collect ultra-pure phloem sap.

Metabotype variation in a field population of tansy plants influences aphid host selection

It is well known that plant volatiles influence herbivores in their selection of a host plant; however, less is known about how the nonvolatile metabolome affects herbivore host selection. Metabolic diversity between intraspecific plants can be characterized using non-targeted mass spectrometry that gives us a snapshot overview of all metabolic processes occurring within a plant at a particular time. Here, we show that non-targeted metabolomics can be used to reveal links between intraspecific chemical diversity and ecological processes in tansy (Tanacetum vulgare). First, we show that tansy plants can be categorized into five subgroups based up on their metabolic profiles, and that these "metabotypes" influenced natural aphid colonization in the field. Second, this grouping was not due to induced metabolomic changes within the plant due to aphid feeding but rather resulted from constitutive differences in chemical diversity between plants. These findings highlight the importance of intraspecific chemical diversity within one plant population and provide the first report of a non-targeted metabolomic field study in chemical ecology.

Zinc is an inhibitor of the LdtR transcriptional activator

LdtR is a master regulator of gene expression in Liberibacter asiaticus, one of the causative agents of citrus greening disease. LdtR belongs to the MarR-family of transcriptional regulators and it has been linked to the regulation of more than 180 genes in Liberibacter species, most of them gathered in the following Clusters of Orthologous Groups: cell motility, cell wall envelope, energy production, and transcription. Our previous transcriptomic evidence suggested that LdtR is directly involved in the modulation of the zinc uptake system genes (znu) in the closely related L. crescens. In this report, we show that LdtR is involved in the regulation of one of the two encoded zinc uptake mechanisms in L. asiaticus, named znu2. We also show that LdtR binds zinc with higher affinity than benzbromarone, a synthetic effector inhibitory molecule, resulting in the disruption of the LdtR:promoter interactions. Using site-directed mutagenesis, electrophoretic mobility shift assays (EMSAs), and isothermal titration calorimetry, we identified that residues C28 and T43 in LdtR, located in close proximity to the Benz1 pocket, are involved in the interaction with zinc. These results provided new evidence of a high-affinity effector molecule targeting a key player in L. asiaticus' physiology and complemented our previous findings about the mechanisms of signal transduction in members of the MarR-family.

Behavioral Plasticity in Probing by Diaphorina citri (Hemiptera, Liviidae): Ingestion from Phloem Versus Xylem is Influenced by Leaf Age and Surface

Diaphorina citri is a major pest of citrus because it transmits Candidatus Liberibacter asiaticus, a phloem-limited bacterium that putatively causes Huanglongbing (HLB). The disease moves slowly through a tree, and the vector facilitates further within-tree movement via transmission of the pathogen. However, this only happens when D. citri stylets contact the phloem, to inoculate bacteria during phloem salivation and acquire bacteria during phloem sap ingestion. Behavioral changes in D. citri associated with different plant parts would affect how long it takes to reach phloem and how long the psyllids stays in phloem to ingest, thereby influencing the risk of disease spread. D. citri feeding was recorded on the abaxial and adaxial surfaces of mature and immature citrus leaves. Adults in the field can be found on these surfaces at all times of year. On abaxial surface of immature leaves, phloem salivation would occur after 11 h on average, but rarely as soon as 0.56 h. The corresponding values on mature leaves were 16 and 2.7. In general, psyllids spent more time ingesting phloem sap on immature leaves than on mature leaves. Psyllids on abaxial surfaces spent more time ingesting from phloem, though the strength of this effect was less than for immature versus mature leaves. In contrast, xylem ingestion increased on mature leaves compared with young. The biological differences that could produce this outcome are discussed. The results discussed herein are of relevance to further studies on the efficacy of an insecticide to act quickly enough to prevent pathogen transmission.