Floral Nectary Morphology and Proteomic Analysis of Nectar of Liriodendron tulipifera Linn

Ubiquitin-like and ubiquitinylated proteins associated with the maternal cell walls of Scenedesmus obliquus 633 as identified by immunochemistry and LC-MS/MS proteomics

The cell walls of green algae Scenedesmus obliquus are complex, polymeric structures including an inner cellulose layer surrounded by an algaenan-containing trilaminar sheath. The process of autosporulation leads to the formation of sporangial (maternal) cell walls, which are released into the medium after sporangial autolysis. In this study, a fraction of maternal cell wall material (CWM) was isolated from the stationary phase cultures of Scenedesmus obliquus 633 and subjected to immunofluorescence microscopy using polyclonal anti-ubiquitin antibodies. The water-extracted polypeptide fraction from the maternal cell walls was then analyzed using immunoblotting and LC-MS/MS. An immunoanalysis showed the presence of several peptides reactive with polyclonal anti-ubiquitin serum, with apparent molecular masses of c. 12, 70, 120, 200, and > 250 kDa. Cell wall-associated peptides were identified on the basis of LC-MS/MS spectra across NCBI databases, including the Scenedesmaceae family (58 records), the Chlorophyceae class (37 records), and Chlamydomonas reinhardtii (18 records) corresponding to the signatures of 95 identified proteins. In particular, three signatures identified ubiquitin and ubiquitin-related proteins. In the maternal cell walls, immunoblotting analysis, immunofluorescence microscopy, and LC-MS/MS proteomics collectively demonstrated the presence of ubiquitin-like epitopes, ubiquitin-specific peptide signatures, and several putative ubiquitin conjugates of a higher molecular mass. These results support the presence of ubiquitin-like proteins in the extramembranous compartment of Scenedesmus obliquus 633 and suggest that protein ubiquitination plays a significant role in the formation and functional integrity of the maternal cell walls in green algae.

Coryanthes macrantha (Orchidaceae: Stanhopeinae) and their floral and extrafloral secretory structures: an anatomical and phytochemical approach

Coryanthes is one of the most fascinating genera of Stanhopeinae (Orchidaceae) because of its complex pollination mechanism and the peculiar structures of its flowers. Although Coryanthes macrantha is widely studied, investigation of the secretory structures and floral biology is important to understand the mechanisms and ecology of pollination, which deserve attention despite the difficulties of collecting fertile material in nature. We conducted a morpho-anatomical analysis of the floral and extrafloral secretory structures of C. macrantha to better understand the secretory structures, contribute to the knowledge of its floral biology and/or pollination processes and understand the ecological function of these structures. The analysis revealed that C. macrantha has epidermal osmophores with unicellular papillae that were foraged by male Eulaema bees, floral nectaries in the sepals and extrafloral nectaries in the bracts. In both the floral and extrafloral nectaries, the nectar is exuded by the stomata. Azteca ants foraged the bract and sepal nectaries in pre-anthesis and post-anthesis. We also described the secretory epidermis of pleuridia, and the mode of secretion of osmophores and nectaries and found that they attract specific foraging agents.

Identification, Phylogenetic and Expression Analyses of the AAAP Gene Family in Liriodendron chinense Reveal Their Putative Functions in Response to Organ and Multiple Abiotic Stresses

In this study, 52 AAAP genes were identified in the L. chinense genome and divided into eight subgroups based on phylogenetic relationships, gene structure, and conserved motif. A total of 48 LcAAAP genes were located on the 14 chromosomes, and the remaining four genes were mapped in the contigs. Multispecies phylogenetic tree and codon usage bias analysis show that the LcAAAP gene family is closer to the AAAP of Amborella trichopoda, indicating that the LcAAAP gene family is relatively primitive in angiosperms. Gene duplication events revealed six pairs of segmental duplications and one pair of tandem duplications, in which many paralogous genes diverged in function before monocotyledonous and dicotyledonous plants differentiation and were strongly purification selected. Gene expression pattern analysis showed that the LcAAAP gene plays a certain role in the development of Liriodendron nectary and somatic embryogenesis. Low temperature, drought, and heat stresses may activate some WRKY/MYB transcription factors to positively regulate the expression of LcAAAP genes to achieve long-distance transport of amino acids in plants to resist the unfavorable external environment. In addition, the GAT and PorT subgroups could involve gamma-aminobutyric acid (GABA) transport under aluminum poisoning. These findings could lay a solid foundation for further study of the biological role of LcAAAP and improvement of the stress resistance of Liriodendron.

Agrobacterium-Mediated Genetic Transformation of Embryogenic Callus in a Liriodendron Hybrid (L. Chinense × L. Tulipifera)

A highly efficient genetic transformation system of Liriodendron hybrid embryogenic calli through Agrobacterium-mediated genetic transformation was established and optimized. The Agrobacterium tumefaciens strain EHA105, harboring the plasmid pBI121, which contained the ß-glucuronidase (GUS) gene and neomycin phosphotransferase II (npt II) gene under the control of the CaMV35S promoter, was used for transformation. Embryogenic calli were used as the starting explant to study several factors affecting the Agrobacterium-mediated genetic transformation of the Liriodendron hybrid, including the effects of various media, selection by different Geneticin (G418) concentrations, pre-culture period, Agrobacterium optical density, infection duration, co-cultivation period, and delayed selection. Transformed embryogenic calli were obtained through selection on medium containing 90 mg L-1 G418. Plant regeneration was achieved and selected via somatic embryogenesis on medium containing 15 mg L-1 G418. The optimal conditions included a pre-culture time of 2 days, a co-culture time of 3 days, an optimal infection time of 10 min, and a delayed selection time of 7 days. These conditions, combined with an OD600 value of 0.6, remarkably enhanced the transformation rate. The results of GUS chemical tissue staining, polymerase chain reaction (PCR), and southern blot analysis demonstrated that the GUS gene was successfully expressed and integrated into the Liriodendron hybrid genome. A transformation efficiency of 60.7% was achieved for the regenerated callus clumps. Transgenic plantlets were obtained in 5 months, and the PCR analysis showed that 97.5% of plants from the tested G418-resistant lines were PCR positive. The study of the Liriodendron hybrid reported here will facilitate the insertion of functional genes into the Liriodendron hybrid via Agrobacterium-mediated transformation.

Transcriptome and proteome analysis suggest enhanced photosynthesis in tetraploid Liriodendron sino-americanum

Polyploidy generally provides an advantage in phenotypic variation and growth vigor. However, the underlying mechanisms remain poorly understood. The tetraploid Liriodendron sino-americanum (Liriodendron × sinoamericanum P.C Yieh ex C.B. Shang & Zhang R.Wang) exhibits altered morphology compared with its diploid counterpart, including larger, thicker and deeper green leaves, bigger stomata, thicker stems and increased tree height. Such characteristics can be useful in ornamental and industrial applications. To elucidate the molecular mechanisms behind this variation, we performed a comparative transcriptome and proteome analysis. Our transcriptome data indicated that some photosynthesis genes and pathways were differentially altered and enriched in tetraploid L. sino-americanum, mainly related to F-type ATPase, the cytochrome b6/f complex, photosynthetic electron transport, the light harvesting chlorophyll protein complexes, and photosystem I and II. Most of the differentially expressed proteins we could identify are also involved in photosynthesis. Our physiological results showed that tetraploids have an enhanced photosynthetic capacity, concomitant with great levels of sugar and starch in leaves. This suggests that tetraploid L. sino-americanum might experience comprehensive transcriptome reprogramming of genes related to photosynthesis. This study has especially emphasized molecular changes involved in photosynthesis that accompany polyploidy, and provides a possible explanation for the altered phenotype of polyploidy plants in comparison with their diploid form.

Integrative analysis of transcriptome and proteome revealed nectary and nectar traits in the plant-pollinator interaction of Nitraria tangutorum Bobrov

BACKGROUND

Nitraria tangutorum is an important desert shrub that shows resistance to drought, salt and wind erosion stresses. It is a central ecological species in its area. Here, we have studied how N. tangutorum has adapted to achieve a successful reproduction strategy.

RESULTS

We found that N. tangutorum is mainly pollinated by insects of the Hymenoptera, Diptera and Coleoptera orders. Nitraria tangutorum has very small flowers, with the nectary composed of secretive epidermal cells from which nectar is secreted, located within the inner petals. In addition, analyzing the transcriptome of four successive flower developmental stages revealed that mainly differentially expressed genes associated with flower and nectary development, nectar biosynthesis and secretion, flavonoid biosynthesis, plant hormone signal transduction and plant-pathogen interaction show dynamic expression. From the nectar, we could identify seven important proteins, of which the L-ascorbate oxidase protein was first found in plant nectar. Based on the physiological functions of these proteins, we predict that floral nectar proteins of N. tangutorum play an important role in defending against microbial infestation and scavenging active oxygen.

CONCLUSIONS

This study revealed that N. tangutorum is an insect-pollinated plant and its nectary is composed of secretive epidermal cells that specialized into secretive trichomes. We identified a large number of differentially expressed genes controlling flower and nectary development, nectar biosynthesis and secretion, flavonoid biosynthesis, plant hormone signal transduction and plant-pathogen interaction. We suggest that proteins present in N. tangutorum nectar may have both an antibacterial and oxygen scavenging effect. These results provide a scientific basis for exploring how the reproductive system of N. tangutorum and other arid-desert plants functions.

A single honey proteome dataset for identifying adulteration by foreign amylases and mining various protein markers natural to honey

Honey adulteration is a common practice that deceives consumers and devalues the unique curative and food properties of honey. For marketing, each honey must satisfy an internationally valid Codex standard. One of the quality parameters is diastase/amylase activity, which, if lowered, may be compensated for by the addition of foreign amylases. However, the estimation of enzyme activity does not enable identification of artificially added amylases. 45 honey samples were analyzed using label-free nanoLC-MS/MS proteomics. Four honeys were found to contain the foreign amylases from Aspergillus niger, Bacillus amyloliquefaciens and/or Bacillus licheniformis. This result was confirmed via proof of specificity at multiple levels. Furthermore, we identified a series of plant-related protein groups. Despite plant-related proteins constituting a significant portion of honey proteins, they were minor components compared to the major honey bee-derived proteins. Bioinformatic analysis also provided evidence for aphid and catalase proteins in honey, but the limited specificity of the MS/MS identified peptides must be considered. Overall, we demonstrate a proteomics approach employing LC-MS/MS that is useful for proving adulteration and assessing honey quality. As an resource useful for reference, we provide curated sequence databases. In addition, we provide many markers that are naturally found in honey for future studies. SIGNIFICANCE: Honey is unique natural product used since ancient times as a food and natural medicine. Humans strive to understand honey components because they can characterize different types of honey and be used for authentication and origin assessment. One of the important honey components are proteins. The proteins present in honey can naturally occur in honey, but some of them can be used to mask deficiencies in some honey quality properties. Diastases/amylases are such proteins, and their activity, a measure of honey freshness, can decrease in time or due to processing. To our knowledge, we for the first time specifically identify foreign amylases in honey. However, this study provided new information on other non-honey bee proteins in honey. Thus, this study is also of importance due to its identification of plant and aphid proteins and catalase-related proteins. This study provides a clue explaining the controversial presence of catalase in honey, since catalases can be identified and their origin determined via proteomics.

The Fungal Endophyte Epicoccum dendrobii as a Potential Biocontrol Agent Against Colletotrichum gloeosporioides

Anthracnose caused by Colletotrichum gloeosporioides is one of most serious fungal diseases on Chinese fir (Cunninghamia lanceolata). Eight fungal endophytes were isolated from a young heathy branch of Chinese fir and screened against the pathogen in vitro. One isolate, designated as SMEL1 and subsequently identified as Epicoccum dendrobii based on morphological and phylogenetic analyses, suppressed mycelial growth of Colletotrichum gloeosporioides on dual-culture plates. Additionally, E. dendrobii metabolites significantly decreased the biomass of Colletotrichum gloeosporioides. E. dendrobii was able to enter the internal tissues of the host plant via stomatal cells. Metabolites of E. dendrobii significantly inhibited conidial germination and appressorium formation, which at least partly explained why the endophyte significantly inhibited lesion development caused by Colletotrichum gloeosporioides on various host plants. We further confirmed that some components with antifungal activity could be extracted from E. dendrobii using ethyl acetate as an organic solvent. To our knowledge, this is the first report of E. dendrobii as a potential biocontrol agent against a fungal phytopathogen.

Transcriptome analysis and metabolic profiling reveal the key role of carotenoids in the petal coloration of Liriodendron tulipifera

Liriodendron tulipifera, also known as tuliptree, is a popular ornamental horticultural plant with extraordinary tulip-shaped flowers characterized by an orange band near their base. The mechanisms underlying petal band-specific pigmentation during L. tulipifera flower development are unclear. Here, we combined nontargeted and targeted metabolomics and transcriptomics to identify a pathway cascade leading to carotenoid biosynthesis that is specifically activated in the petal band. The comparative analysis of carotenoid metabolites between L. tulipifera and Liriodendron hybrids indicates that γ-carotene, a rare carotene in plants, is the most likely orange pigment responsible for the coloration of the petal band. Phenotypic and transcriptomic analyses of developing petals reveal that the band area is first predefined by the loss of green color. Later, the band is maintained by locally activating and repressing carotenoid and chlorophyll biosynthesis genes, respectively. Two rate-limiting genes of carotene biosynthesis, carotenoid isomerase (CRTISO) and epsilon lycopene cyclase (ε-LCY), encode the core enzymes responsible for petal band-specific orange pigmentation in L. tulipifera. In particular, a putative additional ε-LCY copy specific to L. tulipifera may contribute to the distinct petal coloration pattern, compared with L. chinense. Taken together, our work provides a first glimpse of the metabolome and transcriptome dynamics in tuliptree flower coloration and provides a valuable resource for flower breeding or metabolic engineering as well as for understanding flower evolution in an early woody angiosperm.

LC-MS/MS based comparative proteomics of floral nectars reveal different mechanisms involved in floral defense of Nicotiana spp., Petunia hybrida and Datura stramonium

Tobacco floral nectar (FN) is a biological fluid produced by nectaries composed of sugars, amino acids and proteins called nectarins, involved in the floral defense. FN provides an ideal source of nutrients for microorganisms. Understanding the role of nectar proteins is essential to predict impacts in microbial growth, composition and plants-pollinators interactions. Using LC-MS/MS-based comparative proteomic analysis we identified 22 proteins from P. hybrida, 35 proteins from D. stramonium, and 144 proteins from 23 species of Nicotiana. The data are available at ProteomeXchance (PXD014760). GO analysis and secretory signal prediction demonstrated that defense/stress was the largest group of proteins in the genus Nicotiana. The Nicotiana spp. proteome consisted of 105 exclusive proteins such as lipid transfer proteins (LTPs), Nectar Redox Cycle proteins, proteases inhibitors, and PR-proteins. Analysis by taxonomic sections demonstrated that LTPs were most abundant in Undulatae and Noctiflora, while nectarins were more abundant in Rusticae, Suaveolens, Polydicliae, and Alata sections. Peroxidases (Pox) and chitinases (Chit) were exclusive to P. hybrida, while D. stramonium had only seven unique proteins. Biochemical analysis confirmed these differences. These findings support the hypothesis that, although conserved, there is differential abundance of proteins related to defense/stress which may impact the mechanisms of floral defense. SIGNIFICANCE: This study represents a comparative proteomic analysis of floral nectars of the Nicotiana spp. with two correlated Solanaceous species. Significant differences were identified between the proteome of taxonomic sections providing relevant insights into the group of proteins related to defense/stress associated with Nectar Redox Cycle, antimicrobial proteins and signaling pathways. The activity of FNs proteins is suggested impact the microbial growth. The knowledge about these proteomes provides significant insights into the diversity of proteins secreted in the nectars and the array of mechanisms used by Nicotiana spp. in its floral defense.

Transcriptomic and microstructural analyses in Liriodendron tulipifera Linn. reveal candidate genes involved in nectary development and nectar secretion

BACKGROUND

Nectar is a major floral attractant and reward for insects that ensures pollination. Liriodendron, a genus of the Magnoliaceae family, includes only two relict species, L. chinense and L. tulipifera, which are considered "basal angiosperms" according to plant evolutionary history. The flowers of Liriodendron plants are insect pollinated and secrete nectar to attract pollinators. To date, the morphology and anatomy of nectaries, the mechanism of nectar secretion and the molecular mechanism of nectary development in Liriodendron remain poorly understood.

METHODS

In this study, we examined the nectary surface cells and change in starch in L. tulipifera by using scanning electron microscopy and periodic acid-Schiff techniques to select appropriate samples for subsequent research. Transcriptome sequencing was of the top and middle parts of immature nectaries and the middle part of mature and postsecretory nectaries in L. tulipifera was performed. We evaluated the expression profiles of 21 DEGs that are closely related to nectary development and nectar secretion for real-time quantitative PCR analysis.

RESULTS

L. tulipifera nectaries are starch-storing nectaries and are located in the top and middle parts of L. tulipifera petals. After analyzing the RNA-seq data, we obtained 115.26 Gb of clean data in 12 libraries and mapped the results to the L. chinense reference genome with 71.02-79.77% efficiency. In total, 26,955 DEGs were identified by performing six pairwise comparisons. The flavonoid biosynthesis, phenylpropanoid biosynthesis, anthocyanin biosynthesis and starch and sucrose metabolism pathways were enriched and related to nectar secretion and pigment change. We identified 56 transcription factor families, and members of the TCP, Trihelix, C2H2, ERF, and MADS families changed dynamically during nectary development. Moreover, to further verify the accuracy of the RNA-seq results, we validated the expression profiles of 21 candidate genes.

CONCLUSIONS

We evaluated the nectary development and secretion processes comprehensively and identified many related candidate genes in L. tulipifera. These findings suggest that nectaries play important roles in flavonoid synthesis and petal color presentation.

Proteomics and post-secretory content adjustment of Nicotiana tabacum nectar

MAIN CONCLUSION

The tobacco nectar proteome mainly consists of pathogenesis-related proteins with two glycoproteins. Expression of nectarins was non-synchronous, and not nectary specific. After secretion, tobacco nectar changed from sucrose rich to hexose rich. Floral nectar proteins (nectarins) play important roles in inhibiting microbial growth in nectar, and probably also tailoring nectar chemistry before or after secretion; however, very few plant species have had their nectar proteomes thoroughly investigated. Nectarins from Nicotiana tabacum (NT) were separated using two-dimensional gel electrophoresis and then analysed using mass spectrometry. Seven nectarins were identified: acidic endochitinase, β-xylosidase, α-galactosidase, α-amylase, G-type lectin S-receptor-like serine/threonine-protein kinase, pathogenesis-related protein 5, and early nodulin-like protein 2. An eighth nectarin, a glycoprotein with unknown function, was identified following isolation from NT nectar using a Qproteome total glycoprotein kit, separation by SDS-PAGE, and identification by mass spectrometry. Expression of all identified nectarins, plus four invertase genes, was analysed by qRT PCR; none of these genes had nectary-specific expression, and none had synchronous expression. The total content of sucrose, hexoses, proteins, phenolics, and hydrogen peroxide were determined at different time intervals in secreted nectar, both within the nectar tube (in vivo) and following extraction from it during incubation at 30 °C for up to 40 h in plastic tubes (in vitro). After secretion, the ratio of hexose to sucrose substantially increased for in vivo nectar, but no sugar composition changes were detected in vitro. This implies that sucrose hydrolysis in vivo might be done by fixed apoplastic invertase. Both protein and hydrogen peroxide levels declined in vitro but not in vivo, implying that some factors other than nectarins act to maintain their levels in the flower, after secretion.

Cloning, Characterization and Functional Analysis of the LtuPTOX Gene, a Homologue of Arabidopsis thaliana IMMUTANS Derived from Liriodendron tulipifera

Flower colour and colour patterns are crucial traits for ornamental species; thus, a comprehensive understanding of their genetic basis is extremely significant for plant breeders. The tulip tree (Liriodendron tulipifera Linn.) is well known for its flowers, odd leave shape and tree form. However, the genetic basis of its colour inheritance remains unknown. In this study, a putative plastid terminal oxidase gene (LtuPTOX) was identified from L. tulipifera based on multiple databases of differentially expressed genes at various developmental stages. Then, the full-length cDNA of LtuPTOX was derived from tepals and leaves using RACE (rapid amplification of cDNA ends) approaches. Furthermore, gene structure and phylogenetic analyses of PTOX as well as AOXs (alternative oxidases), another highly similar homologue in the AOX family, were used to distinguish between the two subfamilies of genes. In addition, transient transformation and qPCR methods were used to determine the subcellular localization and tissue expression pattern of the LtuPTOX gene. Moreover, the expression of LtuPTOX as well as pigment contents was investigated to illustrate the function of this gene during the formation of orange bands on petals. The results showed that the LtuPTOX gene encodes a 358-aa protein that contains a complete AOX domain (PF01786). Accordingly, the LiriodendronPTOX and AOX genes were identified as only paralogs since they were rather similar in sequence. LtuPTOX showed chloroplast localization and was expressed in coloured organs such as petals and leaves. Additionally, an increasing pattern of LtuPTOX transcripts leads to carotenoid accumulation on the orange-band during flower bud development. Taken together, our results suggest that LtuPTOX is involved in petal carotenoid metabolism and orange band formation in L. tulipifera. The identification of this potentially involved gene will lay a foundation for further uncovering the genetic basis of flower colour in L. tulipifera.

Exploring new applications of tulip tree (Liriodendron tulipifera L.): leaf essential oil as apoptotic agent for human glioblastoma

Liriodendron tulipifera L. (Magnoliaceae), also known as "tulip tree," is a hardwood plant native to North America, cultivated all over the world and used on an industrial level, especially for its fine wood and to make honey. It has also been traditionally exploited for its antimalarial properties. However, our knowledge about the bioactivity of its essential oil remains patchy. In this research, we focused on the biological evaluation of the volatile fractions obtained from different parts of the plant which are normally discharged by industry, including leaves, flowers, and fruits. For the purpose, the essential oils were obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry (GC-MS). Then, they were evaluated as radical scavenging, antioxidant, antimicrobial, and antiproliferative agents by using DPPH, ABTS, FRAP, disk diffusion, and MTT methods, respectively. The significant toxicity exhibited on human tumor cells, namely A375 malignant melanoma, HCT116 colon carcinoma, MDA-MB 231 breast adenocarcinoma, and T98G glioblastoma multiforme cell lines, prompted us to study the mechanism of action by acridine orange/ethidium bromide double staining and caspase 3 assays. Our findings shed light on the potential applications of tulip tree derivatives as anticancer drugs.

Integrating Phylogeographic Analysis and Geospatial Methods to Infer Historical Dispersal Routes and Glacial Refugia of Liriodendron chinense

Liriodendron chinense (Hemsl.), a Tertiary relic tree, is mainly distributed in subtropical China. The causes of the geographical distribution pattern of this species are poorly understood. In this study, we inferred historical dispersal routes and glacial refugia of this species by combining genetic data (chloroplast DNA (cpDNA), nuclear ribosomal DNA (nrDNA), and nuclear DNA (nDNA)) and geospatial data (climate and geology) with the methods of landscape genetics. Additionally, based on sequence variation at multiple loci, we employed GenGIS and Barrier software to analyze L. chinense population genetic structure. Dispersal corridors and historical gene flow between the eastern and western populations were detected, and they were located in mountainous regions. Based on species distribution model (SDMs), the distribution patterns in paleoclimatic periods were consistent with the current pattern, suggesting the presence of multiple refuges in multiple mountainous regions in China. The genetic structure analysis clustered most eastern populations into a clade separated from the western populations. Additionally, a genetic barrier was detected between the eastern and western populations. The dispersal corridors and historical gene flow detected here suggested that the mountains acted as a bridge, facilitating gene flow between the eastern and western populations. Due to Quaternary climatic fluctuations, the habitats and dispersal corridors were frequently inhabited by warm-temperate evergreen forests, which may have fragmented L. chinense habitats and exacerbated the differentiation of eastern and western populations. Ultimately, populations retreated to multiple isolated mountainous refugia, shaping the current geographical distribution pattern. These dispersal corridors and montane refugia suggested that the mountains in subtropical China play a crucial role in the conservation of genetic resources and migration of subspecies or related species in this region.

Sex-Dependent Variation of Pumpkin (Cucurbita maxima cv. Big Max) Nectar and Nectaries as Determined by Proteomics and Metabolomics

Nectar is a floral reward that sustains mutualisms with pollinators, which in turn, improves fruit set. While it is known that nectar is a chemically complex solution, extensive identification and quantification of this complexity has been lacking. Cucurbita maxima cv. Big Max, like many cucurbits, is monoecious with separate male and female flowers. Attraction of bees to the flowers through the reward of nectar is essential for reproductive success in this economically valuable crop. In this study, the sex-dependent variation in composition of male and female nectar and the nectaries were defined using a combination of GC-MS based metabolomics and LC-MS/MS based proteomics. Metabolomics analysis of nectar detected 88 metabolites, of which 40 were positively identified, and includes sugars, sugar alcohols, aromatics, diols, organic acids, and amino acids. There are differences in 29 metabolites between male and female nectar. The nectar proteome consists of 45 proteins, of which 70% overlap between nectar types. Only two proteins are unique to female nectar, and 10 are specific to male nectar. The nectary proteome data, accessible at ProteomeXchange with identifier PXD009810, contained 339 identifiable proteins, 71% of which were descriptively annotatable by homology to Plantae. The abundance of 45 proteins differs significantly between male and female nectaries, as determined by iTRAQ labeling. This rich dataset significantly expands the known complexity of nectar composition, supports the hypothesis of H+-driven nectar solute export, and provides genetic and chemical targets to understand plant-pollinator interactions.

Common Features Between the Proteomes of Floral and Extrafloral Nectar From the Castor Plant (Ricinus Communis) and the Proteomes of Exudates From Carnivorous Plants

Label-free quantitative proteome analysis of extrafloral (EFN) and floral nectar (FN) from castor (Ricinus communis) plants resulted in the identification of 72 and 37 proteins, respectively. Thirty proteins were differentially accumulated between EFN and FN, and 24 of these were more abundant in the EFN. In addition to proteins involved in maintaining the nectar pathogen free such as chitinases and glucan 1,3-beta-glucosidase, both proteomes share an array of peptidases, lipases, carbohydrases, and nucleases. A total of 39 of the identified proteins, comprising different classes of hydrolases, were found to have biochemical matching partners in the exudates of at least five genera of carnivorous plants, indicating the EFN and FN possess a potential to digest biological material from microbial, animal or plant origin equivalent to the exudates of carnivorous plants.

Assessment of Multiple Solvents for Extraction and Direct GC-MS Determination of the Phytochemical Inventory of Sansevieria Extrafoliar Nectar Droplets

Considerable effort has been devoted to analytical determinations of sugar and amino acid constituents of plant nectars, with the primary aim of understanding their ecological roles, yet few studies have reported more exhaustive organic compound inventories of plant nectars or extrafoliar nectars. This work evaluated the efficacy of four solvents (ethyl acetate, dichloromethane, toluene and hexane) to extract the greatest number of organic compound classes and unique compounds from extrafoliar nectar drops produced by Sansevieria spp. Aggregation of the results from each solvent revealed that 240 unique compounds were extracted in total, with 42.5% of those detected in multiple extracts. Aliphatic hydrocarbons dominated in all but the ethyl acetate extracts, with 44 unique aliphatic hydrocarbons detected in dichloromethane (DCM) extracts, followed by 41, 19 and 8 in hexane, toluene and ethyl acetate extracts, respectively. Hexane extracted the most unique compounds (79), followed by DCM (73), ethyl acetate (56) and toluene (32). Integrated total ion chromatographic peak areas of extracted compound classes were positively correlated with numbers of unique compounds detected within those classes. In addition to demonstrating that multi-solvent extraction with direct GC-MS detection is a suitable analytical approach for determining secondary nectar constituents, to the best of our knowledge, this study also represents: (i) the first attempt to inventory the secondary phytochemical constituents of Sansevieria spp. extrafoliar nectar secretions and (ii) the largest organic solvent extractable compound inventory reported for any plant matrix to date.

Shoot Blight on Chinese Fir (Cunninghamia lanceolata) is Caused by Bipolaris oryzae

Chinese fir (Cunninghamia lanceolata) is a significant timber species that has been broadly cultivated in southern China. A shoot blight disease on Chinese fir seedlings was discovered in Fujian, China and a fungus was then consistently associated with the symptoms. This fungus was determined to be causing this disease, among others by fulfilling Koch's postulates. Based on morphological characteristics and multilocus phylogenetic analyses with the sequences of the internal transcribed spacer, partial glyceraldehyde-3-phosphate dehydrogenase gene, partial translation elongation factor 1-α gene, and partial 28S large subunit ribosomal RNA gene, the fungus was identified as Bipolaris oryzae. These characteristics and phylogenetic analyses clearly support that this pathogen is different from B. sacchari, which was, until now, considered to be the causal agent of a similar blight on Chinese fir in Guangdong, China. The fungus was also shown to be strongly pathogenic to rice, one of the most susceptible hosts to B. oryzae. Crop rotation involving rice is often carried out with Chinese fir in southern China, a practice that most likely increases the risk of shoot blight on C. lanceolata. To our knowledge, shoot blight caused by B. oryzae is reported for the first time in a gymnosperm species.

Floral Metabolism of Sugars and Amino Acids: Implications for Pollinators' Preferences and Seed and Fruit Set

New discoveries open up future directions in the study of the primary metabolism of flowers.

Review: Nectar biology: From molecules to ecosystems

Plants attract mutualistic animals by offering a reward of nectar. Specifically, floral nectar (FN) is produced to attract pollinators, whereas extrafloral nectar (EFN) mediates indirect defenses through the attraction of mutualist predatory insects to limit herbivory. Nearly 90% of all plant species, including 75% of domesticated crops, benefit from animal-mediated pollination, which is largely facilitated by FN. Moreover, EFN represents one of the few defense mechanisms for which stable effects on plant health and fitness have been demonstrated in multiple systems, and thus plays a crucial role in the resistance phenotype of plants producing it. In spite of its central role in plant-animal interactions, the molecular events involved in the development of both floral and extrafloral nectaries (the glands that produce nectar), as well as the synthesis and secretion of the nectar itself, have been poorly understood until recently. This review will cover major recent developments in the understanding of (1) nectar chemistry and its role in plant-mutualist interactions, (2) the structure and development of nectaries, (3) nectar production, and (4) its regulation by phytohormones.

Floral nectar of the obligate outcrossing Canavalia gladiata (Jacq.) DC. (Fabaceae) contains only one predominant protein, a class III acidic chitinase

Floral nectar can affect the fitness of insect-pollinated plants, through both attraction and manipulation of pollinators. Self-incompatible insect-pollinated plants receive more insect visits than their self-compatible relatives, and the nectar of such species might face increased risk of infestation by pathogens carried by pollinators than self-compatible plants. Proteins in nectar (nectarins) play an important role in protecting the nectar, but little is known regarding nectarins in self-incompatible species. The nectarins from a self-incompatible and insect-pollinated leguminous crop, Canavalia gladiata, were separated using two-dimensional electrophoresis and analysed using mass spectrometry. The predominant nectarin gene was cloned and the gene expression pattern investigated using quantitative real-time PCR. Chitinolytic activity in the nectar was tested with different substrates. The C. gladiata nectar proteome only has one predominant nectarin, an acidic class III chitinase (CaChi3). The full-length CaChi3 gene was cloned, coding for a protein of 298 amino acids with a predicted signal peptide. CaChi3 is very similar to members of the class III chitinase family, whose evolution is dominated by purifying selection. CaChi3 was expressed in both nectary and leaves. CaChi3 has thermostable chitinolytic activity according to glycol-chitin zymography or a fluorogenic substratem but has no lysozyme activity. Chitinase might be a critical protein component in nectar. The extremely simple nectar proteome in C. gladiata disproves the hypothesis that self-incompatible species always have more complex nectar proteomes. Accessibility of nectar might be a significant determinant of the evolutionary pressure to develop nectar defence mechanisms.