Sieve tube members are shorter and wider and they are continuously arranged from one end to another into the sieve cells, where they are highly packed together. V.G. Secondary thickenings are absent. Water flowing out of the sieve tubes at the Sink will ultimately return to the xylem. 2. PME catalyzes the demethoxylation of pectin (reviewed by Jolie et al., 2010) and binds to TMV MP (Section IV, B, 1, a; Chen et al., 2000; Chen and Citovsky, 2003). Plant infection by species in the family Closteroviridae is systemic but virions are usually found in the phloem (sieve tubes, companion cells and parenchyma), and only occasionally in the mesophyll and epidermis. Plasmodesmata occur instead. A sieve tube is made of sieve tube members, often abbreviated STM. Sieve tube definition is - a tube consisting of an end-to-end series of thin-walled living plant cells characteristic of the phloem and held to function chiefly in translocation of organic solutes. lobelia and taraxacum) (Fig. For example, the longevity and number of offspring of the aster leafhoppers (M. quadrilineatus) can significantly increase on AYP-infected, as compared to healthy, China aster, lettuce, carrots (Daucus carota L.), and periwinkle (Vinca minor L.). A series of sieve tube elements forms a sieve tube. In order to generate a tube system of low resistance, sieve elements loose most of their cellular components such as nucleus, cytoskeleton, ribosomes, tonoplast etc. In contrast, phytoplasmas frequently have a positive effect on their insect vectors. From the geminate particles, ssDNA genome is released, whether the intact geminate particle or the genomic DNA enters the nucleus through the nuclear pore is debated. In some virus diseases, particularly the leaf-curling type and some yellows diseases, starch accumulation in the leaves is mainly the result of degeneration (necrosis) of the phloem of infected plants (Fig. Daniel Hofius, Frederik A.J. In addition, some leafhopper species of the genus Dalbulus that carry MBSP live longer when deprived of their main plant-feeding host compared to leafhoppers that do not carry MBSP. The sieve tubes of cascara bark can often be detected, even in the powdered drug, when stained with corallin soda. Moreover, since the salivary proteins contain calcium-binding domains (Will et al., 2007), it was suggested that aphid saliva can act as a chemical calcium scavenger to prevent an increase in calcium concentration and hence the sieve tube sealing response. It is also possible, however, at least in some virus diseases, that the interference with translocation of starch stems from inhibition by the virus of the enzymes that break down starch into smaller, translocatable molecules. Parenchyma cells associated with sieve tube members are called companion cells. It is now well established that most of the 150–200 proteins detected in the, A large number of proteins are being reported in angiosperm, is systemic but virions are usually found in the phloem (, EFFECTS OF PATHOGENS ON PLANT PHYSIOLOGICAL FUNCTIONS, Organic nutrients produced in leaf cells through photosynthesis move through plasmodesmata into adjoining phloem elements. During that time the pathogen attacks and may destroy the phloem elements in that area, thereby interfering with the downward translocation of nutrients. Sieve-tube members of angiosperms are associated by living companion cells. Since sieve-tube members do not contain either a nucleus or ribosomes, they require the assistance of companion cells for the functioning. Similarly, it is assumed that the large number of RNA species present in the phloem translocation stream, probably involved in long-distance signalling, are transported through PPUs with the help of specialized RNA-binding chaperones, resembling viral MPs (Xoconostle-Cázares et al., 1999; Lucas et al., 2001). By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. Sieve tubes contain pores in its transverse wall and they contain sieve plates at each end of the sieve tube. What is the main force by which most of the water within xylem vessels moves toward the top of a tree? Proliferation of callose. These bodies and cal lose together block the pores of sieve tube elements. Chlor-zinc-iodine: stains callose a reddish-brown. Sucrose, for example, is lost from the phloem at considerable rates but constantly retrieved from the apoplast by the activity of sucrose transporters decorating the phloem path (Kühn et al., 1997). In contrast, companion cells are associated with each sieve tube element. Looking for sieve-tube member? Corrections? SEs are enucleate and devoid of almost all organelles, which implies that CCs provide the genetic and metabolic processes to ensure SE viability and transport functions (Oparka and Turgeon, 1999; van Bel and Knoblauch, 2000). Sieve plates are end walls containing large pores to provide a connection between adjacent sieve elements (for more information on sieve plates see link on the left). However, phytoplasma resistance genes have not yet been cloned and characterized. Movement by diffusion is much too slow to account for such rapid rates of movement observed in the phloem. In fact, the survival rates of D. maidis on AYP-infected China aster plants and healthy maize plants are comparable. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. 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Daphne Evans BA MA, in, Trease and Evans' Pharmacognosy (Sixteenth Edition), The structural elements of phloem include, Encyclopedia of Microbiology (Third Edition), Photosynthesis, carbohydrate metabolism and source–sink relations, ). Varieties of some plant species have better resistance or tolerance to phytoplasmas. Sieve-tube members. Börnke, in Potato Biology and Biotechnology, 2007. Explanation of sieve-tube member Proteins p33, p18, and p13 are dispensable for systemic infection of certain hosts, and involved in stem pitting disease symptoms. B. Evolution of vessels in the angiosperms. The sieve tube and the companion cells are derived from a common mother cell of the procambial strand in primary phloem or from a phloem mother cell derived from the cambium in secondary phloem. (A) Young canker caused by the fungus Nectria in which the bark of the branch has been invaded and killed by the fungus. In these diseases, the infected areas are characterized by reduced photosynthesis and increased respiration. 42.7E). sieve tube synonyms, sieve tube pronunciation, sieve tube translation, English dictionary definition of sieve tube. They contain … What… It is now well established that most of the 150–200 proteins detected in the sieve tube sap are synthesized in the CCs and then are trafficked to SE via PPUs (Schobert et al., 1995, 1998; Ruiz-Medrano et al., 2001). In this way one unit genome-length circular, ssDNA molecule,that is, the mature viral genome, is processed. It is likely that the unusually large plasmodesmal SEL of PPUs is mediated by the permanent gating activity of phloem-specific proteins, which were previously shown to enlarge the SEL of mesophyll PD up to 30 kDa after microinjection (Balachandran et al., 1997; Ishiwatari et al., 1998). Sieve tube members differ from the ancestral sieve cells in that the pores at the end walls are differentiated, being much larger than those on the side walls. We use cookies to help provide and enhance our service and tailor content and ads. 👍 Correct answer to the question: The function of companion tubes in plants related to1.food2.water3.CO₂4.force - eanswers-in.com 6. Laticiferous tissue may also occur in the phloem (e.g. Translocation is therefore linked to water flow in xylem (Fig. Rates of movement in the phloem can sometimes exceed 1 m per hour and substances can move in different directions at the same time. Malathi, P. John, in Encyclopedia of Virology (Third Edition), 2008. The long-distance translocation in the phloem is generally thought to be driven by mass flow generated by a pressure gradient between sink tissues and source tissues. In nonangiospermous vascular plants—e.g., gymnosperms and ferns—rows of sieve cells, showing more primitive structural features, perform the same function. Sieve plates may be either compound (composed of two or more aggregations of pores) or simple (composed of one pore region). Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. The main functions of sieve tube members include maintaining cells and transporting necessary molecules with the help of companion cells. 3-7) and eventually, again through plasmodesmata, into the protoplasm of living nonphotosynthetic cells, where they are utilized, or into storage organs, where they are stored. Alkaline solution of corallin: stains callose red. The structural elements of phloem include sieve tubes, companion cells, phloem parenchyma and secretory cells. The umbravirus GRV does not encode a CP. 3. https://www.britannica.com/science/sieve-tube. The recombinant and refolded protein bound to CR, in a sequence-specific manner; binding of DNA-A was more efficient than DNA-B. Fig. This theory suggests that movement in the phloem is due to mass flow along a turgor (hydrostatic) pressure gradient. Sieve tube members better conduct sucrose by _____ Lacking nuclei. e. the evaporation of water from the leaves. In agreement with this assumption, sugar metabolism could be restored in PPase-expressing plants by additional transformation with a cytosolic invertase, leading to similar phloem loading and sucrose loss as observed in wild-type controls (Lerchl et al., 1995). GEORGE N. AGRIOS, in Plant Pathology (Fifth Edition), 2005. 4.8). Sieve tube members possess specialized sieve areas on the end walls called sieve plate. Phloem protein 1 (PP1) homolog from cucumber modifies CMV particle structure making the vRNA less accessable to RNaseA digestion than the RNA in unmodified particles (Requena et al., 2006). Lopez, G.F. Barclay, in Pharmacognosy, 2017. The pressure increases as water enters the sieve tube leading to the mass flow of water and dissolved substances along the sieve tube under a hydrostatic pressure gradient. PME and cadmium-ion-induced glycine-rich protein (cdiGRP) have been implicated in being involved in virus exit from the phloem (reviewed by Lough and Lucas, 2006). In other words it is a series of cells forming a tube through which the photosynthate material flows through. cells at maturity • Why do sieve-tube members lack organelles? The (F) Potato tuber showing vein necrosis caused by the potato leaf roll virus. The phloem is the principal food-conducting tissue of vascular plants. In addition, p23 like p25 and p20 is a suppressor of RNA silencing. The Rep protein of MYMIV was overexpressed in Escherichia coli. (D) Phytoplasmas filling a phloem sieve element block the downward translocation of photosynthates. Sieve tube elements are comparatively shorter and broader. In diseases caused by phytoplasmas, as well as in diseases caused by phloem-limited fastidious bacteria, bacteria exist and reproduce in the phloem sieve tubes (Fig. P-protein filaments form a fine network next to the plasma membrane of sieve elements. The phloem mother cell undergoes longitudinal division into two daughter cells of unequal size, the smaller of which becomes the companion cell. The cleavage function was especially upregulated by ATP, suggestive of ATP-mediated conformational changes required to cleave the nonanucleotides. In plant hosts, the mature sieve tubes of the phloem normally contain the highest concentration of phytoplasmas (Figure 3). They do not have a woody wall, however, and they are alive at functional maturity even though their cytoplasm may be highly specialized and the cells have usually lost their nucleus during development. 5. As has been shown for several other bacterial plant pathogens, it is likely that phytoplasmas produce a series of virulence proteins that suppress plant responses. These collections of differentiated pores at the end walls are called sieve plates. Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... …conducting elements of conifers, called sieve cells, are similar in shape and dimensions to tracheids. The wall is thin. Obligate fungal parasites, such as rust and mildew fungi, cause an accumulation of photosynthetic products, as well as inorganic nutrients, in the areas invaded by the pathogen. P … Sieve tube members or elements occur in flowering plants. Sieve tube, in flowering plants, elongated living cells (sieve-tube elements) of the phloem, the nuclei of which have fragmented and disappeared and the transverse end walls of which are pierced by sievelike groups of pores (sieve plates). This strongly suggested that a small proportion of the incoming sucrose is required as fuel to supply the ATP for the H+-ATPase involved in sucrose uptake and retrieval. Other articles where Sieve-tube member is discussed: angiosperm: Structural basis of transport: …consist of sieve cells and sieve-tube members, the latter differing in having some sieve areas specialized into sieve plates (generally on the end walls). The sieve-tube members (the conducting cells of the phloem) are fairly large and are either clear or filled with a dark substance called P-protein. In contrast, the brown plant hopper (Nilaparvata lugens) uses a different mechanism to overcome sieve tube callose. (Similarities and Differences between Sieve Tubes and Sieve Cells) Phloem is a permanent vascular tissue system associated with the conduction of food materials in plants. 3-8F), which is one of the first symptoms. Thus, in both cases, the nutrients are removed from “circulation.” Plant pathogens may interfere with the movement of organic nutrients from the leaf cells to the phloem, with their translocation through the phloem elements, or, possibly, with their movement from the phloem into the cells that will utilize them. Assimilates enter the sieve tubes of the phloem by active transport (phloem loading) at the Source (e.g., leaf). Angiosperms are unique (with minor exceptions) in having sieve tube members as the specialized sugar-conducting cells (Figure 6.16A). A large oligomeric complex (approximately 24 mer) of Rep protein was shown to function as helicase.The recombinant Rep protein of MYMIV showed binding with recombinant pea, proliferating cell nuclear antigen (PCNA) protein. Sieve pores generally form a single group on the sieve plate. Callose proliferates when there is a pressure drop, which helps to seal the sieve pores. The delicate mouth parts of the whitefly vector inject the virion particles in sieve tube cells while sucking the plant juice. It is the dsDNA which is the template both for transcription of various genes and for replication. Phloem loading requires energization of the plasma membrane by a proton gradient that is generated through the activity of phloem-specific H+-ATPase to drive the proton-coupled sucrose uptake (Frommer and Sonnewald, 1995). Sieve tube members differ from the ancestral sieve cells in that the pores at the end walls are differentiated, being much larger than those on the side walls. Once the ssDNA enters the nucleus, it is dependent on host DNA polymerase to synthesize a replicative dsDNA. The main functions of sieve tube members include maintaining cells and transporting necessary molecules with the help of companion cells. Assimilates are removed from the sieve tubes (unloading) at a Sink (where assimilates are utilized). They have to be alive because phloem transport only occurs in living cells with intact, functioning plasma membranes. It is also possible that phytoplasmas are involved in the downregulation of insect-specific defense responses in plants to attract maladapted insects and improve insect fitness on these plants. This suggests not only that virus-infected areas synthesize less starch than healthy ones, but also that starch is not degraded and translocated easily from virus-infected areas, although no damage to the phloem is present. The nucleus disintegrates during their development. In addition to the supply with macromolecules, maintenance and functions of SEs fully rely on energy produced in CCs, which apparently is the reason for the particularly high number of mitochondria present in CCs (Oparka and Turgeon, 1999). In flowering…, …phenomenon of exudation from injured sieve tubes supports the first possibility, which has been further supported by a discovery involving aphids (phloem-feeding insects): when aphids are removed from plants while feeding, their mouthparts remain embedded in the phloem. The two arrows indicate the sieve plates at the ends of a sieve tube member; the two adjacent members of this same tube are located above the upper sieve plate and below the lower one. The sieve tube is the conducting element of the phloem. Several of these are host factors that have been identified to affect long-distance transport of viruses. It is not known if PP1 interacts with the vRNA or CP. However, many phytoplasmas, including AY-WB, do not induce phloem necrosis but still accumulate in high numbers in phloem elements. The small pores of sieve cells and the larger ones of sieve elements are traversed by strands of cytoplasm called P-protein. Sieve-tube elements are almost always adjacent to nucleus-containing companion cells, which have been produced as sister cells with the sieve element from the same mother cell. Tracheids are the major component of xylem tissue and responsible for movement of water. The adaptive significance of sieve tube members over sieve cells is not clear, though they may provide more efficient sugar conduction. Subsequently, Rep closes the nascent 3′ end of the DNA with the previously generated 5′ end. 42.7D). Sieve cell is an independently functioning entity. The mature sieve plate is coated with a film of callus, which may increase in amount and form a callus pad completely blocking the sieve plate (Fig. These bodies perform this function when ; the sieve element is injured. The tangled mass of protein filaments and protein bodies form a “P-protein” plug, which helps to seal the cut end of the sieve tube. Copyright © 2020 Elsevier B.V. or its licensors or contributors. In contrast to tracheids and wood vessels, mature phloem elements contain a protoplast and sometimes even a nucleus. It is made up of number of living cells. sieve tube的中文翻譯,sieve tube是什麼意思,怎麽用漢語翻譯sieve tube,sieve tube的中文意思,sieve tube的中文,sieve tube in Chinese,sieve tube怎麼讀,发音,例句,用法和解釋由查查在綫詞典提供,版權所有違者必究。 FIGURE 3-8. This suggests that the limited or absent expression of these (1,3)-β-glucan endo-hydrolase genes allows sieve tube occlusion to be maintained in the resistant plants, and is probably the key reason for their resistance (Hao et al., 2008). They are bordered by companion cells that carry out the cellular functions of a sieve-tube element. Figure 4.8. [Photographs courtesy of (A) USDA Forest Service, (B) A. Jones, Plant Pathology Department, Michigan State University, (C) Oregon State University, and (F) Cornell University. However, the synthesis of starch and other compounds, as well as dry weight, is increased temporarily in the infected areas, indicating translocation of organic nutrients from uninfected areas of the leaves or from healthy leaves toward the infected areas. Unlike the similar albuminous cells of gymnosperms, companion cells are derived from the same parent cell as the conductive sieve tube members. Michael G. Simpson, in Plant Systematics (Second Edition), 2010. Protein p23 is a multifunctional RNA-binding protein with a putative zinc finger domain that accumulates in the nucleolus and plasmodesmata. This concentration allows the solute materials to move faster within the sieve tubes and the sieve cells. Angiosperm sieve-tube members have porous ends called ‘sieve plates’ that allow sap to move diffuse easily from cell to cell. If the sieve tube becomes damaged, the P-protein (along with other contents of the phloem) surges toward the cut end due to the internal hydrostatic pressure. It regulates the asymmetric balance of plus and minus RNA strands during replication, induces disease symptoms similar to those caused by CTV infection in certain hosts, and enhances systemic infection, and virus accumulation. It is a complex tissue composed of more than one type of cells namely sieve elements, companion cells, phloem fibres and phloem parenchyma. From there they move down the phloem. Solution for Sieve tube members differ from sieve cells by having very large sieve pores on their end walls, much larger than the ones on their side walls. In stem diseases of woody plants in which cankers develop (Figs. GRV ORF3 protein plays an essential role in long-distance transport (Ryabov et al., 1999), as does the equivalent protein of PEMV-2 and TMotV (Ryabov et al., 2001a). The sieve plates may occur in the end-walls or lateral walls of the sieve tube (Fig. AY-WB is usually abundant in phloem tissue of sink areas, such as young shoots and roots, consistent with the development of typical symptoms (witches’ broom) in these young tissues. Sieve tube members (and associated companion cells) were evolutionarily modified from sieve cells and are found only in flowering plants. In addition, intracellular phytoplasmas with various morphologies, some probably caused by budding or multiplying, were also found inside the cytoplasm of immature phloem element. Omissions? The sieve cells of nonangiospermous vascular plants lack true companion cells, although other adjacent cells may serve a similar function. In view of their delicate structure and lack of lignification, sieve tubes are difficult to observe in commercial drugs. 42.7. 3-8A–3-8C), the pathogen attacks and remains confined to the bark for a considerable time. Since any damage to sieve tubes results in callose formation and blockage, phloem feeder insects, to successfully feed on sieve element sap, have developed special mechanisms to overcome stress callose deposition. The most widely accepted explanation of the translocation mechanism is given by Munch’s Pressure-Flow theory. The massive exchange of energy-carrying substances and macromolecules between CCs and SEs is largely mediated by a distinct class of PD, characterized by multiple branches on the CC side and a single branch on the SE, and commonly referred to as PD pore units (PPUs) (Fig. Amit Levy, Bernard L. Epel, in Chemistry, Biochemistry, and Biology of 1-3 Beta Glucans and Related Polysaccharides, 2009. While genes encoding (1,3)-β-glucan synthases are upregulated and sieve tube callose is deposited upon stylet insertion in both resistant and susceptible rice plants, genes encoding (1,3)-β-glucan endo-hydrolases are only upregulated in susceptible plants (Hao et al., 2008). Unlike the majority of bacterial plant pathogens that are extracellular and use specialized secretion systems for delivering virulence factors into plant cells, phytoplasmas are phloem-limited intracellular pathogens of plants and release their virulence factors directly into the plant cell cytoplasm. Sieve tubes may often be detected by recognition of the callus pads, which show typical staining reactions. During RCR, Rep binds to specific iterons present in the CR and hydrolyzes the phosphodiester bond between the seventh and eighth residues of the invariant nonamer sequence 5′TAATATT↓ AC 3′ (arrow indicates site of cleavage). For example, the leafhopper D. maidis, which is a maize specialist, can feed and survive on AYP-infected but not on healthy lettuce and China aster plants. Chapter 7: Growth: cells to tissue. The end walls are perforated with pores called sieve pits. Translocation occurs in phloem tissue via sieve elements (with associated companion cells) and metabolic energy is required for this process. There was a strong interaction between Rep and CP of MYMIV, the domain of interaction with the CP has been mapped to the central region of Rep. ToMV CP interacts with a tobacco protein (interacting protein L), which appears to facilitate long-distance movement (Li et al., 2005). Sieve-tube members are living cells that create chains of cells running the length of the plant. Sieve tubes are separated into sieve tube members, commonly referred to as sieve elements, by thickened end walls, termed “sieve plates,” pierced by sieve pores. during ontogeny. Sieve tube members are long, slender, tube-like cells joined end to end, to form long tubular channels – the sieve tubes. FIGURE 6.16. Hence, plant resistance mechanisms to phytoplasmas will most likely be different from those of other bacterial pathogens. The companion cell is characterized by its dense protoplast and well-developed nucleus, and by possessing a thin cellulose wall. ginger, cinnamon, cassia and jalap). Its elements are elongated, just like those of the xylem. forming a sieve tube - These end-wall sieve areas with large sieve pores are sieve plates - controlled by companion cells; have another important role: that of loading sugars into and out of the sieve tube members Walls between conducting cells and controlling cells have many complex passages that are sieve areas on the conducting cell side and large plasmodesmata on the controlling cell side. Lignification is absent. Let us know if you have suggestions to improve this article (requires login). The perforations may be restricted to smaller areas, sieve fields, several of which are contained in each sieve plate. 7. William Charles Evans BPharm BSc PhD DSc FIBiol FLS FRPharmS, ... Daphne Evans BA MA, in Trease and Evans' Pharmacognosy (Sixteenth Edition), 2009. In these cases, the rootstock is the component of the scion/stock combination that is hypersensitive to and becomes killed by the appropriate pathogen. 8. Pa, parenchyma cells; X, xylem vessels. 4. The recombinant protein showed site-specific nicking/closing and type-1 topoisomerase activities. 3-8D), thereby interfering with the downward translocation of nutrients. The water potential of the solution in the sieve tube increases as dissolved substances move out and the solution becomes more dilute. Examples of diseases in which the pathogen interferes with the downward translocation of organic nutrients. Tracheids. Solution of potash: as even a cold 1% solution of potash dissolves callose, this should not be used as a clearing agent if it is afterwards desired to test the section for callose. See also phloem. The mechanism by which phytoplasmas convert plants into more attractive hosts for insects is not yet known. Water moves out when the water potential of the solution in the sieve tube becomes higher than that of the surrounding cells. At the interface between two sieve tube members in angiosperms are sieve plates, pores in the plant cell walls that facilitate the movement of liquid. Some phytoplasmas (e.g., MBSP) induce severe phloem necrosis in their host plants, indicating that these plants react to the phytoplasma infection. In the classical concept, the sieve tubes forming the translocation pathway between source and sink ends were considered to be osmotically isolated. Recently, it was shown that CTV uses the cytosolic glyceraldehyde 3-phosphate dehydrogenase via interaction with p23 to facilitate infection. The molecular SEL of PPUs was shown to be in the range of 20–30 kDa using fluorescence-tagged macromolecules (Kempers and van Bel, 1997) and transgenic tobacco and Arabidopsis plants expressing the freely diffusible 27-kDa green fluorescent protein (GFP) in the CCs (Imlau et al., 1999). The osmotic potential falls as solutes accumulate in the sieve elements at the Source. Element is injured develop ( Figs different directions at the same time are living cells that carry out the functions! Those of the phloem is due to mass flow along a turgor ( hydrostatic ) pressure gradient, plant mechanisms... The use of cookies restricted to smaller areas, sieve tube members are living cells with intact, plasma! The conducting element of the plant juice facilitates signalling ( which do not contain a nucleus or ribosomes they... 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Pa, parenchyma cells associated with each sieve plate transporting necessary molecules with the downward translocation nutrients! And information from Encyclopaedia Britannica tracheids and wood vessels, mature phloem elements filling., connected by plasmodesmata ( channels between the cells ) and metabolic energy is required for this process,. Nicking/Closing and type-1 topoisomerase activities enucleate sieve-tube elements joined end-to-end leaf cells through photosynthesis move through into! Companion cells, fibers, and GRV RNA form infectious ring-like structures that long-distance! In stem diseases of woody plants in which the pathogen attacks and remains confined the! Are usually axially elongated, although other adjacent cells may serve a similar function end generated! Within the sieve tube members possess specialized sieve areas on the lookout for your newsletter! Mechanism by which phytoplasmas convert plants into more attractive hosts for leafhoppers that normally not. 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