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The aim of this study was to evaluate whether citreorosein (CIT), a naturally occurring anthraquinone isolated from Polygoni cuspidati (P. cuspidati) radix, modulates degranulation and 5-lipoxygenase (5-LO)-dependent leukotriene [C.sub.4] ([LTC.sub.4]) generation in mast cells. Cit suppresses both degranulation and the generation of [LTC.sub.4] in a dose-dependent manner in stem cell factor (SCF)-mediated mouse bone marrow-derived mast cells (BMMCs). With regard to its molecular mechanism of action, we investigated the effects of CIT on intracellular signaling and mast cell activation employing BMMCs. Binding of SCF to c-Kit on mast cell membranes induced increases in intrinsic tyrosine kinase Syk activity and activation of multiple downstream events including phosphorylation of phospholipase C[gamma] (PLC[gamma]), mobilization of intracellular [Ca.sup.2+], phosphatidylinositol 3-kinase (PI3K), Akt, MAP kinases (MAPKs), translocation of phosphophospholipase [A.sub.2] ([PLA.sub.2]) and 5-LO. The results from the biochemical analysis demonstrate that CIT attenuates degranulation and [LTC.sub.4] generation through the suppression of multiple step signaling and would be beneficial for the prevention of allergic inflammation. Keywords Citreorosein * Mast cells * 5-Lipoxygenase * Leukotriene [C.sub.4] * Fyn * Syk kinase * MAP kinase * Intracellular [Ca.sup.2+] * Cytosolic phospholipase [A.sub.2]

Pollen-specific receptor-like kinase 6 (PRK6), which signals through the guanine nucleotide-exchange factors ROPGEFs, is required for sensing of the LURE1 attractant peptide in Arabidopsis thaliana , and functions together with other PRK family kinases; when introduced into the pollen tubes of the related species Capsella rubella , PRK6 could confer responsiveness to AtLURE1. Multiple pollen-tube receptors for LURE1 In flowering plants, the female gametophyte secretes chemoattractant peptides to guide pollen tube growth so that it delivers the immobile sperm to the ovule-enclosed female gametophyte. Two papers published in this issue of Nature report the identification of male pollen tube cell-surface receptors for one of these female attractants, LURE1, in the model plant Arabidopsis thaliana . Wei-Cai Yang and colleagues show that LURE1 is perceived by a receptor-like kinase complex, the heteromer MDIS1–MIK. Tetsuya Higashiyama and Hidenori Takeuchi report that pollen-specific receptor-like kinase 6 (PRK6) is required for sensing LURE1, and PRK6 acts together with other PRK family receptors. Both groups demonstrate that by engineering pollen tubes of the sister species Capsella rubella to express a component of the A. thaliana receptors — either MDIS1 or PRK6 — the reproductive isolation barrier between the two species is partially broken down. Directional control of tip-growing cells is essential for proper tissue organization and cell-to-cell communication in animals and plants 1 , 2 . In the sexual reproduction of flowering plants, the tip growth of the male gametophyte, the pollen tube, is precisely guided by female cues to achieve fertilization 3 . Several female-secreted peptides have recently been identified as species-specific attractants that directly control the direction of pollen tube growth 4 , 5 , 6 . However, the method by which pollen tubes precisely and promptly respond to the guidance signal from their own species is unknown. Here we show that tip-localized pollen-specific receptor-like kinase 6 (PRK6) with an extracellular leucine-rich repeat domain is an essential receptor for sensing of the LURE1 attractant peptide in Arabidopsis thaliana under semi- in-vivo conditions, and is important for ovule targeting in the pistil. PRK6 interacted with pollen-expressed ROPGEFs (Rho of plant guanine nucleotide-exchange factors), which are important for pollen tube growth through activation of the signalling switch Rho GTPase ROP1 (refs 7 , 8 ). PRK6 conferred responsiveness to AtLURE1 in pollen tubes of the related species Capsella rubella . Furthermore, our genetic and physiological data suggest that PRK6 signalling through ROPGEFs and sensing of AtLURE1 are achieved in cooperation with the other PRK family receptors, PRK1, PRK3 and PRK8. Notably, the tip-focused PRK6 accumulated asymmetrically towards an external AtLURE1 source before reorientation of pollen tube tip growth. These results demonstrate that PRK6 acts as a key membrane receptor for external AtLURE1 attractants, and recruits the core tip-growth machinery, including ROP signalling proteins. This work provides insights into the orchestration of efficient pollen tube growth and species-specific pollen tube attraction by multiple receptors during male–female communication.

We report the identification and characterization of a low tocopherol Arabidopsis thaliana mutant, vitamin E pathway gene5-1 (vte5-1), with seed tocopherol levels reduced to 20% of the wild type. Map-based identification of the responsible mutation identified a G[rightwards arrow]A transition, resulting in the introduction of a stop codon in At5g04490, a previously unannotated gene, which we named VTE5. Complementation of the mutation with the wild-type transgene largely restored the wild-type tocopherol phenotype. A knockout mutation of the Synechocystis sp PCC 6803 VTE5 homolog slr1652 reduced Synechocystis tocopherol levels by 50% or more. Bioinformatic analysis of VTE5 and slr1652 indicated modest similarity to dolichol kinase. Analysis of extracts from Arabidopsis and Synechocystis mutants revealed increased accumulation of free phytol. Heterologous expression of these genes in Escherichia coli supplemented with free phytol and in vitro assays of recombinant protein produced phytylmonophosphate, suggesting that VTE5 and slr1652 encode phytol kinases. The phenotype of the vte5-1 mutant is consistent with the hypothesis that chlorophyll degradation-derived phytol serves as an important intermediate in seed tocopherol synthesis and forces reevaluation of the role of geranylgeranyl diphosphate reductase in tocopherol biosynthesis.

In plants, the mevalonic acid (MVA) pathway provides precursors for the formation of triterpenes, sesquiterpenes, phytosterols and primary metabolites important for cell integrity. Here, we have cloned the cDNA encoding enzymes catalysing the final three steps of the MVA pathway from Madagascar periwinkle (Catharanthus roseus), mevalonate kinase (MVK), 5-phosphomevalonate kinase (PMK) and mevalonate 5-diphosphate decarboxylase (MVD). These cDNA were shown to functionally complement MVA pathway deletion mutants in the yeast Saccharomyces cerevisiae. Transient transformations of C. roseus cells with yellow fluorescent protein (YFP)-fused constructs reveal that PMK and MVD are localised to the peroxisomes, while MVK was cytosolic. These compartmentalisation results were confirmed using the Arabidopsis thaliana MVK, PMK and MVD sequences fused to YFP. Based on these observations and the arguments raised here we conclude that the final steps of the plant MVA pathway are localised to the peroxisome.

We previously reported Agrobacterium-mediated transformation methods for the liverwort Marchantia polymorpha using the hygromycin phosphotransferase gene as a marker for selection with hygromycin. In this study, we developed three additional markers for M. polymorpha transformation: the gentamicin 3'-acetyltransferase gene for selection with gentamicin; a mutated acetolactate synthase gene for selection with chlorsulfuron; and the neomycin phosphotransferase II gene for selection with G418. Based on these four marker genes, we have constructed a series of Gateway binary vectors designed for transgenic experiments on M. polymorpha. The 35S promoter from cauliflower mosaic virus and endogenous promoters for constitutive and heat-inducible expression were used to create these vectors. The reporters and tags used were Citrine, 3×Citrine, Citrine-NLS, TagRFP, tdTomato, tdTomato-NLS, GR, SRDX, SRDX-GR, GUS, ELuc(PEST), and 3×FLAG. These vectors, designated as the pMpGWB series, will facilitate molecular genetic analyses of the emerging model plant M. polymorpha.

The human microbiome encodes a large repertoire of biochemical enzymes and pathways, most of which remain uncharacterized. Here, using a metagenomics-based search strategy, we discovered that bacterial members of the human gut and oral microbiome encode enzymes that selectively phosphorylate a clinically used antidiabetic drug, acarbose 1 , 2 , resulting in its inactivation. Acarbose is an inhibitor of both human and bacterial α-glucosidases 3 , limiting the ability of the target organism to metabolize complex carbohydrates. Using biochemical assays, X-ray crystallography and metagenomic analyses, we show that microbiome-derived acarbose kinases are specific for acarbose, provide their harbouring organism with a protective advantage against the activity of acarbose, and are widespread in the microbiomes of western and non-western human populations. These results provide an example of widespread microbiome resistance to a non-antibiotic drug, and suggest that acarbose resistance has disseminated in the human microbiome as a defensive strategy against a potential endogenous producer of a closely related molecule. Bacteria in the human gut and oral microbiome encode enzymes that selectively phosphorylate the antidiabetic drug acarbose—an inhibitor of both human and bacterial α-glucosidases—resulting in its inactivation and limiting the drug's effects on the ability of the host to metabolize complex carbohydrates.

The rapid emergence of RNA therapeutics has highlighted the need for more efficient, scalable and sustainable methods for their manufacture. Biocatalytic approaches hold particular promise, but rely on a secure, sustainable and low-cost supply of nucleoside triphosphate (NTP) building blocks, including those containing chemical modifications. Here we report the development of a biocatalytic approach and engineered enzymes to convert widely available nucleosides into NTPs featuring pharmaceutically relevant modifications using inexpensive phosphate donors. Importantly our strategy obviates the need for ATP as a phosphate donor that complicates NTP isolation using existing methods. To showcase the utility of our approach, we employ an engineered acid phosphatase, polyphosphate kinase and acetate kinase to produce 2′- O -methoxyethyl-ATP (2′-MOE-ATP) and 2′-fluoro-ATP, key building blocks of commercial therapeutics. Finally, we show that crude NTPs from our process can be used directly in enzymatic oligonucleotide synthesis, obviating the need for costly NTP isolation or purification steps. Nucleoside triphosphates (NTPs) are important building blocks that underpin emerging enzymatic approaches to RNA therapeutics manufacturing. Here, authors develop a biocatalytic strategy to convert nucleosides into NTPs containing clinically relevant modifications, using simple phosphate donors.

Plasmodium falciparum malaria is fatal if left untreated. Treatment is hampered by drug-resistant variants of the malaria parasite, highlighting the need to explore unique pathways for the development of new drugs with different mechanisms of action. Kinases in the inositol phosphate signaling pathway (IPP), and its products play many important roles in energy metabolism and signal transduction, making them attractive drug targets. In this exploratory study we investigated the potential of P. falciparum IPP as a novel and attractive pathway for antimalarial drug discovery, employing a combined in silico and molecular approach. The sequences and structures of the putative P. falciparum inositol phosphate kinases were characterized in silico. Experimental validation across laboratory strains and a clinical isolate confirmed the p.Pro375Gln substitution in IPMK1, providing the first evidence of this variant in field isolates. We provide molecular evidence of the existence of IPP genes in P. falciparum and suggest that targeting this pathway could be detrimental to the parasite. We identify P. falciparum inositol polyphosphate multikinase (IPMK) as a promising drug target due to its unique sequence and structural characteristics. These results serve as a guide for future experimental validation.

A male cell-surface receptor-like kinase that responds to the female chemoattractant LURE1 on the pollen tube of Arabidopsis thaliana is identified; LURE1 triggers dimerization of the receptor components and activation of the kinase activity, and the transformation of a component of the A. thaliana receptor to the Capsella rubella species partially breaks down the reproductive isolation barrier. Multiple pollen-tube receptors for LURE1 In flowering plants, the female gametophyte secretes chemoattractant peptides to guide pollen tube growth so that it delivers the immobile sperm to the ovule-enclosed female gametophyte. Two papers published in this issue of Nature report the identification of male pollen tube cell-surface receptors for one of these female attractants, LURE1, in the model plant Arabidopsis thaliana . Wei-Cai Yang and colleagues show that LURE1 is perceived by a receptor-like kinase complex, the heteromer MDIS1–MIK. Tetsuya Higashiyama and Hidenori Takeuchi report that pollen-specific receptor-like kinase 6 (PRK6) is required for sensing LURE1, and PRK6 acts together with other PRK family receptors. Both groups demonstrate that by engineering pollen tubes of the sister species Capsella rubella to express a component of the A. thaliana receptors — either MDIS1 or PRK6 — the reproductive isolation barrier between the two species is partially broken down. Sexual reproduction requires recognition between the male and female gametes. In flowering plants, the immobile sperms are delivered to the ovule-enclosed female gametophyte by guided pollen tube growth. Although the female gametophyte-secreted peptides have been identified to be the chemotactic attractant to the pollen tube 1 , 2 , 3 , the male receptor(s) is still unknown. Here we identify a cell-surface receptor heteromer, MDIS1–MIK, on the pollen tube that perceives female attractant LURE1 in Arabidopsis thaliana . MDIS1, MIK1 and MIK2 are plasma-membrane-localized receptor-like kinases with extracellular leucine-rich repeats and an intracellular kinase domain. LURE1 specifically binds the extracellular domains of MDIS1, MIK1 and MIK2, whereas mdis1 and mik1 mik2 mutant pollen tubes respond less sensitively to LURE1. Furthermore, LURE1 triggers dimerization of the receptors and activates the kinase activity of MIK1. Importantly, transformation of At MDIS1 to the sister species Capsella rubella can partially break down the reproductive isolation barrier. Our findings reveal a new mechanism of the male perception of the female attracting signals.