Academic literature on the topic 'Major Facilitator Super family'
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Journal articles on the topic "Major Facilitator Super family"
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Motoi, Yuji, Mayumi Saeki, Tomoe Nishimura, Kazufumi Katayama, Noriko Kitamura, Hitoshi Ichikawa, Hiroyuki Miyoshi, Osamu Kaminuma, and Takachika Hiroi. "Establishment of monoclonal antibodies against a novel eosinophil-specific cell surface molecule, major facilitator super family domain containing 10." Immunology Letters 147, no. 1-2 (September 2012): 80–84. http://dx.doi.org/10.1016/j.imlet.2012.07.001.
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Nishimura, Tomoe, Mayumi Saeki, Yuji Motoi, Noriko Kitamura, Akio Mori, Osamu Kaminuma, and Takachika Hiroi. "Selective Suppression of Th2 Cell-Mediated Lung Eosinophilic Inflammation by Anti-Major Facilitator Super Family Domain Containing 10 Monoclonal Antibody." Allergology International 63 (2014): 29–35. http://dx.doi.org/10.2332/allergolint.13-oa-0635.
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Ceasar, S. Antony, Alison Baker, Stephen P. Muench, S. Ignacimuthu, and Stephen A. Baldwin. "The conservation of phosphate-binding residues among PHT1 transporters suggests that distinct transport affinities are unlikely to result from differences in the phosphate-binding site." Biochemical Society Transactions 44, no. 5 (October 15, 2016): 1541–48. http://dx.doi.org/10.1042/bst20160016.
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The plant PHosphate Transporter 1 (PHT1) family of membrane proteins belongs to the major facilitator super family and plays a major role in the acquisition of inorganic phosphate (Pi) from the soil and its transport within the plant. These transporters have been well characterized for expression patterns, localization, and in some cases affinity. Furthermore, the crystal structure of a high-affinity eukaryotic phosphate transporter from the fungus Piriformospora indica (PiPT) has revealed important information on the residues involved in Pi transport. Using multiple-sequence alignments and homology modelling, the phosphate-binding site residues were shown to be well conserved between all the plant PHT1 proteins, Saccharomyces cerevisiae PHO84 and PiPT. For example, Asp 324 in PiPT is conserved in the equivalent position in all plant PHT1 and yeast transporters analyzed, and this residue in ScPHO84 was shown by mutagenesis to be important for both the binding and transport of Pi. Moreover, Asp 45 and Asp 149, which are predicted to be involved in proton import, and Lys 459, which is putatively involved in Pi-binding, are all fully conserved in PHT1 and ScPHO84 transporters. The conserved nature of the residues that play a key role in Pi-binding and transport across the PHT1 family suggests that the differing Pi affinities of these transporters do not reside in differences in the Pi-binding site. Recent studies suggest that phosphate transporters could possess dual affinity and that post-translational modifications may be important in regulating affinity for phosphate.
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D'Cruz, Louise M., Ann Piccirillo, Eric Hyzny, Ashley Menk, Callen Wallace, William F. Hawse, Heather Marie Buechel, et al. "The lysophosphatidylcholine transporter, MFSD2A, is essential for CD8+ memory T cell maintenance and secondary response to infection." Journal of Immunology 202, no. 1_Supplement (May 1, 2019): 122.3. http://dx.doi.org/10.4049/jimmunol.202.supp.122.3.
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Abstract Access to nutrients is critical for an effective T cell immune response to infection. Although transporters for sugars and amino acids have previously been described in the context of the CD8+ T cell immune response, the active transport of exogenous fatty acids has remained enigmatic. Here we discovered the sodium-dependent lysophosphatidylcholine transporter, Major Facilitator Super Family Domain Containing 2a (MFSD2A), is upregulated on activated CD8+ T cells and is required for memory T cell maintenance. MFSD2A deficiency in mice resulted in decreased import of lysophosphatidylcholine (LPC) esterified to long chain fatty acids (LCFAs) into activated CD8+ T cells, and MFSD2A deficient cells are at a competitive disadvantage resulting in reduced memory T cell formation and maintenance and reduced response to secondary infection. Mechanistically, import of LPCs was required to maintain T cell homeostatic turnover, that when lost resulted in a decreased memory T cell pool and thus a reduced secondary response to repeat infection.
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Piccirillo, Ann R., William F. Hawse, Heather M. Buechel, David L. Silver, and Louise M. D’Cruz. "The long chain fatty acid transporter, MFSD2A, is essential for memory CD8+ T cell formation and maintenance." Journal of Immunology 200, no. 1_Supplement (May 1, 2018): 51.3. http://dx.doi.org/10.4049/jimmunol.200.supp.51.3.
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Abstract Access to nutrients is critical for an effective T cell immune response to infection. Although transporters for sugars and amino acids have previously been described in the context of the CD8+ T cell immune response, the active transport of exogenous esterified fatty acids has remained enigmatic. Here we discovered the long chain fatty acid transporter, Major Facilitator Super Family Domain Containing 2a (MFSD2A), is upregulated on activated CD8+ T cells and is essential for their memory cell formation. MFSD2A deficiency resulted in decreased import of long chain fatty acids (LCFAs) esterified to lysophosphatidylcholine (LPC) into activated CD8+ T cells but overall resulted in a normal primary effector T cell response. However, loss of MFSD2A led to reduced memory T cell formation and maintenance. MFSD2A deficient memory CD8+ T cells showed reduced CD127 and CD62L expression and their cell turnover was significantly impaired in contrast to their wildtype counterparts. Moreover, the secondary response to infection was severely diminished in MFSD2A deficient T cells. Mechanistically, import of LCFAs was required to maintain cell energy requirements and ‘fitness’, that when lost resulted in a decreased memory T cell pool and inability to proliferate upon secondary stimulation. Our results show that MFSD2A and LPC may be useful for future small molecule therapy design to generate a more robust T cell response for new vaccines or cancer treatments.
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Pao, Stephanie S., Ian T. Paulsen, and Milton H. Saier. "Major Facilitator Superfamily." Microbiology and Molecular Biology Reviews 62, no. 1 (March 1, 1998): 1–34. http://dx.doi.org/10.1128/mmbr.62.1.1-34.1998.
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SUMMARY The major facilitator superfamily (MFS) is one of the two largest families of membrane transporters found on Earth. It is present ubiquitously in bacteria, archaea, and eukarya and includes members that can function by solute uniport, solute/cation symport, solute/cation antiport and/or solute/solute antiport with inwardly and/or outwardly directed polarity. All homologous MFS protein sequences in the public databases as of January 1997 were identified on the basis of sequence similarity and shown to be homologous. Phylogenetic analyses revealed the occurrence of 17 distinct families within the MFS, each of which generally transports a single class of compounds. Compounds transported by MFS permeases include simple sugars, oligosaccharides, inositols, drugs, amino acids, nucleosides, organophosphate esters, Krebs cycle metabolites, and a large variety of organic and inorganic anions and cations. Protein members of some MFS families are found exclusively in bacteria or in eukaryotes, but others are found in bacteria, archaea, and eukaryotes. All permeases of the MFS possess either 12 or 14 putative or established transmembrane α-helical spanners, and evidence is presented substantiating the proposal that an internal tandem gene duplication event gave rise to a primordial MFS protein prior to divergence of the family members. All 17 families are shown to exhibit the common feature of a well-conserved motif present between transmembrane spanners 2 and 3. The analyses reported serve to characterize one of the largest and most diverse families of transport proteins found in living organisms.
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Grover, Amit, and Rakesh Sharma. "Identification and Characterization of a Major Zn(II) Resistance Determinant of Mycobacterium smegmatis." Journal of Bacteriology 188, no. 19 (October 1, 2006): 7026–32. http://dx.doi.org/10.1128/jb.00643-06.
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ABSTRACT A zinc ion-sensitive mutant of Mycobacterium smegmatis was isolated. The transposon insertion was located in zitA (MSMEG0750), a gene coding for a cation diffusion facilitator family protein. Zinc ions specifically induced expression of zitA. In silico analysis revealed that environmental and opportunistic pathogenic species contain higher numbers of cation diffusion facilitator genes than do obligate pathogens.
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Kumar, Sanath, Manjusha Lekshmi, Ammini Parvathi, Manisha Ojha, Nicholas Wenzel, and Manuel F. Varela. "Functional and Structural Roles of the Major Facilitator Superfamily Bacterial Multidrug Efflux Pumps." Microorganisms 8, no. 2 (February 16, 2020): 266. http://dx.doi.org/10.3390/microorganisms8020266.
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Pathogenic microorganisms that are multidrug-resistant can pose severe clinical and public health concerns. In particular, bacterial multidrug efflux transporters of the major facilitator superfamily constitute a notable group of drug resistance mechanisms primarily because multidrug-resistant pathogens can become refractory to antimicrobial agents, thus resulting in potentially untreatable bacterial infections. The major facilitator superfamily is composed of thousands of solute transporters that are related in terms of their phylogenetic relationships, primary amino acid sequences, two- and three-dimensional structures, modes of energization (passive and secondary active), and in their mechanisms of solute and ion translocation across the membrane. The major facilitator superfamily is also composed of numerous families and sub-families of homologous transporters that are conserved across all living taxa, from bacteria to humans. Members of this superfamily share several classes of highly conserved amino acid sequence motifs that play essential mechanistic roles during transport. The structural and functional importance of multidrug efflux pumps that belong to the major facilitator family and that are harbored by Gram-negative and -positive bacterial pathogens are considered here.
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Pratiwi, Indah D. "Family presence during resuscitation: patient and family members’ preferences and attitudes." International Journal of Research in Medical Sciences 6, no. 2 (January 24, 2018): 394. http://dx.doi.org/10.18203/2320-6012.ijrms20180275.
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Background: This literature review presents a review of the available studies into family presence during resuscitation (FPDR) in the context of emergency department and critical care unit from the point of view of patients and family members. This literature review provides the background for understanding the debate about FPDR. The paper examines the state of current research on the topic and points out gaps in existing literature.Methods: A comprehensive search of OVID Nursing, Web of Science (Web of Knowledge), Elsevier, ProQuest and Google Scholar electronic search engine. Thematic analysis was used to extract themes from the 25 studies reviewed (quantitative, qualitative and mixed-methods studies), resulted in five major themes and five minor themes.Results: Five major themes from this literature review were: (1) patient and family members’ preferences; (2) perceived benefits of family presence during resuscitation; (3) perceiving family presence as a right; (4) the importance of a family facilitator; and (5) the involvement of decision making.Conclusions: This literature review has established the potentials of family presence during resuscitation to improve patient and family-centred care by helping and providing family members to manage and to adjust during traumatic circumstances.
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Sherwood, Peter W., Iskra Katic, Pascual Sanz, and Marian Carlson. "A Glucose Transporter Chimera Confers a Dominant Negative Glucose Starvation Phenotype in Saccharomyces cerevisiae." Genetics 155, no. 2 (June 1, 2000): 989–92. http://dx.doi.org/10.1093/genetics/155.2.989.
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Abstract A family of glucose transporters mediates glucose uptake in Saccharomyces cerevisiae. We show that the dominant mutation GSF4-1, which impairs glucose repression of SUC2, results in a nonfunctional chimera of the transporters Hxt1p and Hxt4p. Hxt1/4p inhibits the function of wild-type glucose transporters. Similar mutations may facilitate analysis of the major facilitator superfamily.
Dissertations / Theses on the topic "Major Facilitator Super family"
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Majumder, Puja. "Structural and Functional Investigation of a Multi-drug Efflux Transporter QacA." Thesis, 2020. https://etd.iisc.ac.in/handle/2005/5103.
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The emergence of multi-drug resistance in bacteria is a global health care challenge. One of the effective means of gaining antimicrobial resistance, among superbugs, is through expression of efflux pumps. Quaternary ammonium compound transporters, QacA/B, that are observed in Staphylococcus aureus strains are capable of transporting 30 chemically dissimilar monovalent and divalent cationic antibacterial compounds and dyes. The 14-TM (transmembrane) helix containing transporter QacA, belongs to the drug/H+ antiporter 2 (DHA2) family which is a part of major facilitator superfamily (MFS). MFS transporters are the largest superfamily of secondary active transporters. QacA utilizes the H+ gradient across the bacterial cell membrane for the uphill efflux of the cytotoxic compounds. QacA has two distinct TM domains, each of which consists of 6-TM helices that retain a pseudo 2-fold symmetry amongst them. During the transport process, the domains move in rocker-switch mechanism to allow alternating-access to either side of the membrane in order to transport the substrates. The expression of this efflux pump is regulated by a trans-acting regulatory DNA binding protein QacR. Under normal condition, QacR blocks the transcription of qacA gene by binding to the operator DNA but under antibacterial stress, the substrates of QacA binds to QacR, causing dissociation of QacR from the operator DNA and QacA gets expressed.
In this thesis, structural and functional investigation of QacA was carried out and some fundamental questions about this multi-drug efflux transporter are addressed. In the first part, wild-type QacA was purified and the transport activity of the transporter both in native membrane and in isolation was analyzed using substrate-induced H+-release assay and a reconstitution-based assay. The binding studies with the cytotoxic substrates (TPP, Pm, Dq) displayed sub-millimolar binding affinity with the purified transporter and substrate/H+ competition assay suggested the presence of substrate-protonation site interactions in QacA. Further, survival assays done in the presence of TPP and Pm and whole cell ethidium efflux assay illustrated that ΔpH provides primary driving energy to the transporter. In the second part of the thesis, six protonatable acidic residues D34, D61, D323, E406, E407 and D411, lining the transport vestibule were identified using a homology model of QacA and each of the residue was characterized using mutagenesis. The binding studies and the transport assays illustrated D34, D323, E407 and D411 are crucial for the transport activity of the transporter either as substrate recognition sites or indirectly facilitating the transport process as protonation sites. The findings of the study suggested the inherent residue level promiscuity for different substrates of QacA, that can explain broad substrate specificities of QacA and other related multi-drug efflux transporters. The third part of the thesis described single-domain Indian camelid antibody (ICab) library generation and isolation of high affinity binders against QacA, in order to stabilize the transporter to facilitate the structural studies. The sorting of the binding population was done using yeast surface display coupled with flow-cytometry and 7 unique ICab binders were isolated. The last part of the thesis is focused on the heterologous expression and purification of two of the camelid antibodies in E. coli through refolding and cytosolic protein preparation. The binding studies using FSEC (fluorescence detection size exclusion chromatography), flow-cytometry and microscale thermophoresis suggested that the purified ICabs bind to the transporter with nanomolar affinity. Furthermore, 2D classes from cryo-electron microscopy of QacA-ICab complex clearly displayed the presence of the transporter in detergent micelles bound to the ICab. Moreover, the effect of ICab on QacA-substrate interactions indicated that ICabs can block substrate binding to the transporter. The results provide an interesting prospect of using the ICabs as efflux pump inhibitors (EPI).
Book chapters on the topic "Major Facilitator Super family"
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Boomsma, Jacobus J. "Necessary and sufficient conditions for major evolutionary transitions." In Domains and Major Transitions of Social Evolution, 78–104. Oxford University PressOxford, 2022. http://dx.doi.org/10.1093/oso/9780198746171.003.0004.
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Abstract From an individual perspective, there is a fundamental difference between cooperation for mutual benefit and self-sacrificing altruism. However, there is no such difference for the gene’s eye view of social evolution, which stipulates that both types of cooperation are equally self-serving. Gene’s eye explanations of altruism started with the pedigree version of Hamilton’s rule, and were later generalized when Price equation logic produced a statistical and fully general genetic theory of social evolution, and an approximate phenotypic theory amenable to empirical testing. However, this generalization applied to societies with redundant partnerships where relatedness is variable and social adaptations are mediated by condition-dependent altruism at the level of cellular or multicellular agents. Under such conditions, adaptations for the exclusive benefits of the higher-level of organizational complexity cannot evolve. Yet, such adaptations of unconditional somatic altruism universally characterize the convergent major evolutionary transitions (MTEs) towards multicellular organismality and colonial superorganismality. I show that the origins of (super)organismality can be conjectured to have required invariably maximal relatedness among cell copies or siblings, owing to lifetime commitment between a pair of gametes or monogamous parents. Such pairwise closure in terms of genetic information partitions Hamilton’s rule in an invariant necessary condition of relatedness equivalence between dispersing and adhering offspring, and a contingent sufficiency condition (b/c > 1) that is additionally required to forge a MTE origin. This implies that (super)organismality MTEs are expected to evolve by directional kin selection for unconditional, obligate altruism by entire cohorts, which is different from individual selection for conditional altruism in societies. I contrast the predictions of the classical continuous version of Hamilton’s rule for social evolution in societies and the partitioned discontinuous version applicable to MTE origins, and argue that conflict reduction and body- or family-size stabilize societies but played no role in the origin of (super)organismality.
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Mishra, Rakesh K. "Potential Role of Nuclear Factor κB in Cardiovascular Disease." In Emerging Applications, Perspectives, and Discoveries in Cardiovascular Research, 43–52. IGI Global, 2017. http://dx.doi.org/10.4018/978-1-5225-2092-4.ch003.
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Lung and Cardiovascular disease creating a major health burden in developed countries and primary cause of deaths. Although treatments have progressed, the development of novel treatments for patients with cardiovascular diseases remains a major research goal. Despite modern advances in pharmacological and interventional cardiology, cardiovascular disease still remains a leading cause of morbidity and mortality in all over the world. The nuclear factor (NF)-?B super family of transcription factors has been implicated in the regulation of immune cell maturation, cell survival, and inflammation in many cell types, including cardiac myocytes. Recent studies have shown that NF-?B is cardioprotective during acute hypoxia and reperfusion injury. NF-kB regulates the gene expression of major pro-inflammatory cytokines (TNF-a, IL-b), chemokines [macrophage inflammatory protein (MIP-2), cytokine-induced neutrophil chemoattractant (CINC)], and adhesion molecules (ICAM-1, E selectin) (2), all of which play a major role in lung injury. However, prolonged activation of NF-?B appears to be detrimental and promotes heart failure by eliciting signals that trigger chronic inflammation through enhanced elaboration of cytokines. In this review, we summarize progresses in understanding the NF-kB pathway in lung and cardio-vascular disease development as well as in modulating NF-kB for prevention and therapy.
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Al-Dahmoshi, Hussein, Sahar A. Ali, and Noor Al-Khafaji. "Efflux Pumps among Urinary E. coli and K. pneumoniae Local Isolates in Hilla City, Iraq." In The Global Antimicrobial Resistance Epidemic – Innovative Approaches and Cutting-Edge Solutions [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.104408.
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Urinary tract infections (UTI) are the most common bacterial infections affecting humans. Escherichia coli and Klebsiella pneumoniae were common enterobacteria engaged with community-acquired UTIs. Efflux pumps were vital resistance mechanisms for antibiotics, especially among enterobacteria. Overexpression of an efflux system, which results in a decrease in antibiotic accumulation, is an effective mechanism for drug resistance. The ATP-binding cassette (ABC) transporters, small multidrug resistance (SMR), and multidrug and toxic compound extrusion (MATE) families, the major facilitator superfamily (MFS), and the resistance-nodulation- cell division (RND) family are the five superfamilies of efflux systems linked to drug resistance. This chapter highlights the results of studying the prevalence of efflux pump genes among local isolates of E. coli and K. pneumoniae in Hilla City, Iraq. class RND AcrAB-TolC, AcrAD-TolC, and AcrFE-TolC genes detected by conventional PCR of E. coli and K. pneumoniae respectively. The result revealed approximately all studied efflux transporter were found in both E. coli and K. pneumoniae in different percentages. Biofilm formation were observed in 50(100%) of K. pneumoniae and 49(98%) of E. coli isolates were biofilm former and follow: 30(60%), 20(40%) were weak, 12(24%), 22(44%) were moderate and 7(14%) and 8(16%) were Strong biofilm former for E. coli and K. pneumoniae, respectively.
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MacDonald, Scott. "Gustav Deutsch." In The Sublimity of Document, 51–72. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780190052126.003.0003.
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Austrian filmmaker Gustav Deutsch has been a major contributor to what has come to be called “found-footage filmmaking” and/or “recycled cinema”—that is, he is best-known for making films from other films. This interview focuses on a range of his projects: his first found-footage project, an exploration of home movies made by Austrians visiting the Italian coast in the years after Super-8mm became a popular film gauge for documenting family events; a collaborative diptych of Place, made with an Algerian friend, comparing the Algerian oasis Figuig and Deutsch’s native Vienna; his revisiting of proto-cinematic technologies in the construction of a panoramic camera obscura on a Greek island; his remarkable feature film Shirley—Visions of Reality (2013) in which he (and his partner Hanna Schimek) dramatize a series of canonical Edward Hopper paintings; and the recent Notes and Sketches 1: 31 Pocket Films. 2005–2015, a panorama of everyday events, made with new camera technologies.
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Huu Trung, Nguyen. "Multiplexing Techniques for Applications Based-on 5G Systems." In Multiplexing - Recent Advances and Novel Applications [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.101780.
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Multiplexing is an important technique in modern communication systems that allows simultaneous transmission of multiple channels of information on the same transmission media. Fifth-generation (5G) mobile communication systems allow Enhanced Mobile Broadband (eMBB), Ultra Reliable Low Latency Communications (URLLC), and Massive Machine Type Communications (mMTC). 5G has carrier frequency bands from sub-1 GHz to mid-bands and millimetre waves. The sub-1 GHz frequency band is for mobile broadband, broadcast and massive IoT applications. The mid-bands (between 1–6 GHz) offer wider bandwidths, focusing on mobile broadband and mission-critical applications. The frequency bands above 24 GHz (mmWaves) support super wide bandwidth applications over short, line-of-sight coverage. For each application on a corresponding frequency band, 5G allows defining of an optimized waveform from a family of waveforms. 5G uses massive MIMO, NOMA and network slicing techniques which allows spatial multiplexing and multibeam multiplexing. Multiplexing techniques play a major role in 5G systems in terms of data rate and bandwidth efficiency. This chapter presents multiplexing techniques for applications based-on 5G systems.
Conference papers on the topic "Major Facilitator Super family"
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Dias, Paulo Jorge, and Isabel Sa-Correia. "Reconstruction of the evolutionary history of the DHA1 family of yeast multidrug resistance transporters of the major facilitator superfamily." In 2011 1st Portuguese Meeting in Bioengineering ¿ The Challenge of the XXI Century (ENBENG). IEEE, 2011. http://dx.doi.org/10.1109/enbeng.2011.6026075.
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Plazos, Danielyn F., Allan Brian I. Cabisay, Rommel C. Ongcay, and Rydell Reade A. Peramide. "Design of Foldable Shelter for Post-Disaster Response." In International Conference on Structural Engineering and Materials. Switzerland: Trans Tech Publications Ltd, 2023. http://dx.doi.org/10.4028/p-68d3t1.
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The Philippines is hit by different calamities and is considered one of the world's most disaster-prone countries, regularly ranking in the top three countries hit most by natural catastrophes. Foldable shelters provide private and secure living spaces for persons forced to leave or lose their usual housing due to a calamity. This study aimed to design a lightweight steel-framed temporary shelter that can withstand typhoon calamities and follows the design requirements mandated by the National Building Code and National Structural Code of the Philippines. The shelter's design concept emphasized its expandability, allowing it to accommodate one family of 4-5 persons. It also is designed to be deploy easily, safe, and efficient in post-disaster settings. The major factors considered when developing the shelter are the ease of assembly process, a compact and flexible structure, and adaptability to rapidly changing conditions. The structural analysis indicates that it can withstand a typhoon with an average wind speed of 220 kph but will fail in a super typhoon like Haiyan, with an average wind speed of 250 kph. Since this shelter is designed for temporary uses, the maximum wind capacity of 220 kph is acceptable and can be a reasonable basis for using these to replace other shelters.
Reports on the topic "Major Facilitator Super family"
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Granot, David, and Richard Amasino. Regulation of Senescence by Sugar Metabolism. United States Department of Agriculture, January 2003. http://dx.doi.org/10.32747/2003.7585189.bard.
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Research objectives a. Analyze transgenic plants that undergo rapid senescence due to increased expression of hexokinase. b. Determine if hexokinase-induced senescence accelerates natural senescence using senescence specific promoters that drive expression of a reporter gene (GUS) and a cytokinin producing gene (IPT - isopentyl transferase). c. Isolate and analyze plant genes that suppress sugar-induced cell death (SICD) in yeast, genes that potentially are involved in programmed cell death and senescence in plants. Background to the topic Leaf senescence is a regulated process of programmed cell death (PCD) in which metabolites are recycled to other active parts of the plant. Senescence associated genes (SAGs) are expressed throughout leaf senescence. Sugar flux and metabolism is thought to playa fundamental regulatory role in senescence. We found that transgenic tomato plants with high hexokinase activity, the initial enzymatic step of sugar (hexose) metabolism, undergo rapid leaf senescence, directly correlated with hexokinase activity. These plants provide a unique opportunity to analyze the regulatory role of sugar metabolism in senescence, and its relation to cytokinin, a senescence-inhibiting hormone. In addition, we found that sugar induces programmed cells death of yeast cells in direct correlation to hexokinase activity. We proposed to use the sugar induced cell death (SICD) to isolate Arabidopsis genes that suppress SICD. Such genes could potentially be involved in senescence induced PCD in plants. Major conclusions The promoters of Arabidopsis senescence-associated genes, SAG12 and SAGI3, are expressed in senescing tomato leaves similar to their expression in Arabidopsis leaves, indicating that these promoters are good senescence markers for tomato plants. Increased hexokinase activity accelerated senescence and induced expression of pSAG12 and pSAG13 promoters in tomato plants, suggesting that sugar regulate natural senescence via hexokinase. Expression of IPT, a cytokinin producing gene, under pSAG12 and pSAG13 promoters, delayed senescence of tomato leaves. Yet, senescence accelerated by hexokinase was epistatic over cytokinin, indicating that sugar regulation of senescence is dominant over the senescence-inhibiting hormone. A gene designated SFP1, which is similar to the major super family monosaccharide transporters, is induced during leaf senescence in Arabidopsis and may be involved in sugar transport during senescence. Accordingly, adult leaves accumulate sugars that may accelerate hexokinase activity. Light status of the entire plant affects the senescence of individual leaves. When individual leaves are darkened, senescence is induced in the covered leaves. However, whole adult plant placed in darkness show delayed senescence. In a search for Arabidopsis genes that suppress SICD we isolated 8 cDNA clones which confer partial resistance to SICD. One of the clones encodes a vesicle associated membrane protein - VAMP. This is the first evidence that vesicle trafficking might be involved in cell death. Implications Increased hexokinase activity accelerates senescence. We hypothesized that, reduced hexokinase activity may delay senescence. Preliminary experiments using a hexokinase inhibitor support this possible implication. Currently we are analyzing various practical approaches to delay leaf senescence via hexokinase inhibition. .
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Gal-On, Amit, Shou-Wei Ding, Victor P. Gaba, and Harry S. Paris. role of RNA-dependent RNA polymerase 1 in plant virus defense. United States Department of Agriculture, January 2012. http://dx.doi.org/10.32747/2012.7597919.bard.
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Objectives: Our BARD proposal on the impact of RNA-dependent RNA polymerase 1 (RDR1) in plant defense against viruses was divided into four original objectives. 1. To examine whether a high level of dsRNA expression can stimulate RDR1 transcription independent of salicylic acid (SA) concentration. 2. To determine whether the high or low level of RDR1 transcript accumulation observed in virus resistant and susceptible cultivars is associated with viral resistance and susceptibility. 3. To define the biogenesis and function of RDR1-dependent endogenous siRNAs. 4. To understand why Cucumber mosaic virus (CMV) can overcome RDR1-dependent resistance. The objectives were slightly changed due to the unique finding that cucumber has four different RDR1 genes. Background to the topic: RDR1 is a key plant defense against viruses. RDR1 is induced by virus infection and produces viral and plant dsRNAs which are processed by DICERs to siRNAs. siRNAs guide specific viral and plant RNA cleavage or serve as primers for secondary amplification of viral-dsRNA by RDR. The proposal is based on our preliminary results that a. the association of siRNA and RDR1 accumulation with multiple virus resistance, and b. that virus infection induced the RDR1-dependent production of a new class of endogenous siRNAs. However, the precise mechanisms underlying RDR1 induction and siRNA biogenesis due to virus infection remain to be discovered in plants. Major conclusions, solutions and achievements: We found that in the cucurbit family (cucumber, melon, squash, watermelon) there are 3-4 RDR1 genes not documented in other plant families. This important finding required a change in the emphasis of our objectives. We characterized 4 RDR1s in cucumber and 3 in melon. We demonstrated that in cucumber RDR1b is apparently a new broad spectrum virus resistance gene, independent of SA. In melon RDR1b is truncated, and therefore is assumed to be the reason that melon is highly susceptible to many viruses. RDR1c is dramatically induced due to DNA and RNA virus infection, and inhibition of RDR1c expression led to increased virus accumulation which suggested its important on gene silencing/defense mechanism. We show that induction of antiviral RNAi in Arabidopsis is associated with production of a genetically distinct class of virus-activated siRNAs (vasiRNAs) by RNA dependent RNA polymerase-1 targeting hundreds of host genes for RNA silencing by Argonaute-2. Production of vasiRNAs is induced by viruses from two different super groups of RNA virus families, targeted for inhibition by CMV, and correlated with virus resistance independently of viral siRNAs. We propose that antiviral RNAi activate broad-spectrum antiviral activity via widespread silencing of host genes directed by vasiRNAs, in addition to specific antiviral defense Implications both scientific and agricultural: The RDR1b (resistance) gene can now be used as a transcription marker for broad virus resistance. The discovery of vasiRNAs expands the repertoire of siRNAs and suggests that the siRNA-processing activity of Dicer proteins may play a more important role in the regulation of plant and animal gene expression than is currently known. We assume that precise screening of the vasiRNA host targets will lead in the near future for identification of plant genes associate with virus diseases and perhaps other pathogens.