The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Robert Turgeon - One of the best experts on this subject based on the ideXlab platform.
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Mechanisms of Phloem Loading.
Current opinion in plant biology, 2018Co-Authors: Cankui Zhang, Robert TurgeonAbstract:The complex form of higher plants requires continuous, balanced transport of nutrients in the Phloem. The initial step of transferring sugars, amino acids, and other materials from photosynthetic cells to the conducting sieve tubes is known as Phloem Loading. Three Phloem Loading mechanisms have been described. The first involves release of sucrose into the apoplast and subsequent retrieval by the Phloem. The initial release step in this process is now known to be mediated by a new class of transporters, the SWEET proteins. In the other two Loading mechanisms, polymer trapping and diffusion, sucrose passes into the Phloem through cytoplasmic channels, the plasmodesmata. Recent models have shed additional light on these mechanisms and their ability to sustain the growth of even the tallest trees.
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Phloem Loading strategies and water relations in trees and herbaceous plants
Plant Physiology, 2011Co-Authors: Lailiang Cheng, Yangdong Guo, Robert TurgeonAbstract:Most herbaceous plants employ thermodynamically active mechanisms of Phloem Loading, whereas in many trees, the mechanism is passive, by diffusion. Considering the different water transport characteristics of herbs and trees, we hypothesized that water relations play a role in the adoption of Phloem Loading strategies. We measured whole-plant hydraulic conductance (Kp), osmolality, concentrations of polar metabolites, and key inorganic ions in recently mature leaves of 45 dicotyledonous species at midafternoon. Trees, and the few herbs that load passively, have low Kp, high osmolality, and high concentrations of transport sugars and total polar metabolites. In contrast, herbs that actively load sucrose alone have high Kp, low osmolality, and low concentrations of sugars and total polar metabolites. Solute levels are higher in sugar alcohol-transporting species, both herbs and trees, allowing them to operate at lower leaf water potentials. Polar metabolites are largely responsible for leaf osmolality above a baseline level (approximately 300 mm) contributed by ions. The results suggest that trees must offset low Kp with high concentrations of foliar transport sugars, providing the motivating force for sugar diffusion and rendering active Phloem Loading unnecessary. In contrast, the high Kp of most herbaceous plants allows them to lower sugar concentrations in leaves. This reduces inventory costs and significantly increases growth potential but necessitates active Phloem Loading. Viewed from this perspective, the elevation of hydraulic conductance marks a major milestone in the evolution of the herbaceous habit, not only by facilitating water transport but also by maximizing carbon use efficiency and growth.
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Phloem Loading, plant growth form, and climate.
Protoplasma, 2010Co-Authors: Anna Davidson, Felix Keller, Robert TurgeonAbstract:Plasmodesmatal frequencies in the Phloem of leaf minor veins vary considerably, suggesting that photoassimilate is loaded into the Phloem by different strategies. The ecophysiological basis for multiple Loading types is unknown. We updated the analysis of van Bel and Gamalei (Plant Cell Environ 15: 265–270, 1992) with more current phylogenetic data and by treating separately two symplastic Loading types, those that load actively by polymer trapping (synthesis of raffinose family oligosaccharides—RFOs), and those that load passively, by diffusion. The results indicate a stronger association between passive, symplastic Loading and the tree growth form than previously recognized. Apoplastic Loading is highly correlated with the herbaceous habit. There is no correlation between RFO families and growth form. At the family level, there are no correlations between minor vein types and climate that cannot be explained by the dearth of woody plants in the arctic for reasons unassociated with Phloem Loading. However, at the species level, a floristic analysis uncovered a correlation between the RFO trait and species frequency in tropical and subtropical regions of the world. The correlations between Loading types and both growth form and climate are subtle, probably indirect, and poorly understood.
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Amborella trichopoda, plasmodesmata, and the evolution of Phloem Loading.
Protoplasma, 2010Co-Authors: Robert Turgeon, Richard MedvilleAbstract:Phloem Loading is the process by which photoassimilates synthesized in the mesophyll cells of leaves enter the sieve elements and companion cells of minor veins in preparation for long distance transport to sink organs. Three Loading strategies have been described: active Loading from the apoplast, passive Loading via the symplast, and passive symplastic transfer followed by polymer trapping of raffinose and stachyose. We studied Phloem Loading in Amborella trichopoda, a premontane shrub that may be sister to all other flowering plants. The minor veins of A. trichopoda contain intermediary cells, indicative of the polymer trap mechanism, forming an arc on the abaxial side and subtending a cluster of ordinary companion cells in the interior of the veins. Intermediary cells are linked to bundle sheath cells by highly abundant plasmodesmata whereas ordinary companion cells have few plasmodesmata, characteristic of Phloem that loads from the apoplast. Intermediary cells, ordinary companion cells, and sieve elements form symplastically connected complexes. Leaves provided with 14CO2 translocate radiolabeled sucrose, raffinose, and stachyose. Therefore, structural and physiological evidence suggests that both apoplastic and polymer trapping mechanisms of Phloem Loading operate in A. trichopoda. The evolution of Phloem Loading strategies is complex and may be difficult to resolve.
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The Role of Phloem Loading Reconsidered
Plant physiology, 2010Co-Authors: Robert TurgeonAbstract:It is generally assumed that the primary role of Phloem Loading is to drive long-distance transport by elevating hydrostatic pressure in sieve elements. This concept is consistent with the fact that, in many plants, energy is used to increase the concentrations of photoassimilates in the leaf Phloem
Margot Bezrutczyk - One of the best experts on this subject based on the ideXlab platform.
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evidence for Phloem Loading via the abaxial bundle sheath cells in maize leaves
The Plant Cell, 2021Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Wolf B Frommer, Colin P S Kruse, Tobias Lautwein, Nora Zollner, Karl Kohrer, Jiyun KimAbstract:Leaves are asymmetric, with different functions for adaxial and abaxial tissue. The bundle sheath (BS) of C3 barley (Hordeum vulgare) is dorsoventrally differentiated into three types of cells: adaxial structural, lateral S-type, and abaxial L-type BS cells. Based on plasmodesmatal connections between S-type cells and mestome sheath (parenchymatous cell layer below bundle sheath), S-type cells likely transfer assimilates toward the Phloem. Here, we used single-cell RNA sequencing to investigate BS differentiation in C4 maize (Zea mays L.) plants. Abaxial BS (abBS) cells of rank-2 intermediate veins specifically expressed three SWEET sucrose uniporters (SWEET13a, b, and c) and UmamiT amino acid efflux transporters. SWEET13a, b, c mRNAs were also detected in the Phloem parenchyma (PP). We show that maize has acquired a mechanism for Phloem Loading in which abBS cells provide the main route for apoplasmic sucrose transfer toward the Phloem. This putative route predominates in veins responsible for Phloem Loading (rank-2 intermediate), whereas rank-1 intermediate and major veins export sucrose from the PP adjacent to the sieve element companion cell complex, as in Arabidopsis thaliana. We surmise that abBS identity is subject to dorsoventral patterning and has components of PP identity. These observations provide insights into the unique transport-specific properties of abBS cells and support a modification to the canonical Phloem Loading pathway in maize.
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Phloem Loading via the abaxial bundle sheath cells in maize leaves
bioRxiv, 2020Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Wolf B Frommer, N Zoellner, Colin P S Kruse, Tobias Lautwein, K E Koehrer, Jiyun KimAbstract:ABSTRACT Leaves are asymmetric, with differential functionalization of abaxial and adaxial tissues. The bundle sheath (BS) surrounding the vasculature of the C3 crop barley is dorsoventrally differentiated into three domains: adaxial structural, lateral S-type, and abaxial L-type. S-type cells seem to transfer assimilates towards the Phloem. Here we used single-cell RNA sequencing to investigate BS differentiation in C4 maize. Abaxial BS (abBS) cells of rank-2 intermediate veins specifically expressed three SWEET sucrose uniporters (SWEET13a, b, and c) and UmamiT amino acid efflux transporters. SWEET13a, b, c were also identified in the Phloem parenchyma (PP). Thus maize acquired a unique mechanism for Phloem Loading in which abBS cells provide the main pathway for apoplasmic sucrose transfer towards the Phloem. This pathway predominates in veins responsible for Phloem Loading (rank-2 intermediate), while rank-1 intermediate and major veins export sucrose from the Phloem parenchyma (PP) adjacent to the sieve element companion cell (SE/CC) complex, as in Arabidopsis. We surmise that abBS identity is subject to dorsoventral patterning and has components of PP identity. These observations provide first insights into the unique transport-specific properties of abBS cells and support for a modification to the canonical Phloem Loading pathway of maize, which may be generalizable to other C4 monocots.
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impaired Phloem Loading in zmsweet13a b c sucrose transporter triple knock out mutants in zea mays
New Phytologist, 2018Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Marc Horschman, Si Nian Char, Jinliang Yang, Bing YangAbstract:Crop yield depends on efficient allocation of sucrose from leaves to seeds. In Arabidopsis, Phloem Loading is mediated by a combination of SWEET sucrose effluxers and subsequent uptake by SUT1/SUC2 sucrose/H+ symporters. ZmSUT1 is essential for carbon allocation in maize, but the relative contribution to apoplasmic Phloem Loading and retrieval of sucrose leaking from the translocation path is not known. Here we analysed the contribution of SWEETs to Phloem Loading in maize. We identified three leaf-expressed SWEET sucrose transporters as key components of apoplasmic Phloem Loading in Zea mays L. ZmSWEET13 paralogues (a, b, c) are among the most highly expressed genes in the leaf vasculature. Genome-edited triple knock-out mutants were severely stunted. Photosynthesis of mutants was impaired and leaves accumulated high levels of soluble sugars and starch. RNA-seq revealed profound transcriptional deregulation of genes associated with photosynthesis and carbohydrate metabolism. Genome-wide association study (GWAS) analyses may indicate that variability in ZmSWEET13s correlates with agronomical traits, especifically flowering time and leaf angle. This work provides support for cooperation of three ZmSWEET13s with ZmSUT1 in Phloem Loading in Z. mays.
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Impaired Phloem Loading in zmsweet13a,b,c sucrose transporter triple knock‐out mutants in Zea mays
The New phytologist, 2018Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Marc Horschman, Si Nian Char, Jinliang Yang, Bing Yang, Wolf B Frommer, Davide SossoAbstract:Crop yield depends on efficient allocation of sucrose from leaves to seeds. In Arabidopsis, Phloem Loading is mediated by a combination of SWEET sucrose effluxers and subsequent uptake by SUT1/SUC2 sucrose/H+ symporters. ZmSUT1 is essential for carbon allocation in maize, but the relative contribution to apoplasmic Phloem Loading and retrieval of sucrose leaking from the translocation path is not known. Here we analysed the contribution of SWEETs to Phloem Loading in maize. We identified three leaf-expressed SWEET sucrose transporters as key components of apoplasmic Phloem Loading in Zea mays L. ZmSWEET13 paralogues (a, b, c) are among the most highly expressed genes in the leaf vasculature. Genome-edited triple knock-out mutants were severely stunted. Photosynthesis of mutants was impaired and leaves accumulated high levels of soluble sugars and starch. RNA-seq revealed profound transcriptional deregulation of genes associated with photosynthesis and carbohydrate metabolism. Genome-wide association study (GWAS) analyses may indicate that variability in ZmSWEET13s correlates with agronomical traits, especifically flowering time and leaf angle. This work provides support for cooperation of three ZmSWEET13s with ZmSUT1 in Phloem Loading in Z. mays.
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impaired Phloem Loading in genome edited triple knock out mutants of sweet13 sucrose transporters
bioRxiv, 2017Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Marc Horschman, Si Nian Char, Jinliang Yang, Bing Yang, Davide Sosso, Wolf B FrommerAbstract:Crop yield depends on efficient allocation of sucrose from leaves to seeds. In Arabidopsis, Phloem Loading is mediated by a combination of SWEET sucrose effluxers and subsequent uptake by SUT1/SUC2 sucrose/H+ symporters. ZmSUT1 is essential for carbon allocation in maize, but the relative contribution to apoplasmic Phloem Loading and retrieval of sucrose leaking from the translocation path is not known. We therefor tested whether SWEETs are important for Phloem Loading in maize. Here we identified three leaf-expressed SWEET sucrose transporters as key components of apoplasmic Phloem Loading in Zea mays L. Notably, ZmSWEET13 paralogs (a, b, c) are among the highest expressed genes in the leaf vasculature. Genome-edited triple knock-out mutants are severely stunted. Photosynthesis of mutants was impaired and leaves accumulated starch and soluble sugars. RNA-seq revealed profound transcriptional deregulation of genes associated with the photosynthetic apparatus and carbohydrate metabolism. GWAS analyses may indicate that variability in ZmSWEET13s is correlated with agronomical traits, specifically flowering time and leaf angle. This work provides support for cooperation of three ZmSWEET13s with ZmSUT1 in Phloem Loading in Zea mays L. Our study highlights these three ZmSWEET13 sucrose transporters as possible candidates for the engineering of crop yield.
Thomas Hartwig - One of the best experts on this subject based on the ideXlab platform.
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evidence for Phloem Loading via the abaxial bundle sheath cells in maize leaves
The Plant Cell, 2021Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Wolf B Frommer, Colin P S Kruse, Tobias Lautwein, Nora Zollner, Karl Kohrer, Jiyun KimAbstract:Leaves are asymmetric, with different functions for adaxial and abaxial tissue. The bundle sheath (BS) of C3 barley (Hordeum vulgare) is dorsoventrally differentiated into three types of cells: adaxial structural, lateral S-type, and abaxial L-type BS cells. Based on plasmodesmatal connections between S-type cells and mestome sheath (parenchymatous cell layer below bundle sheath), S-type cells likely transfer assimilates toward the Phloem. Here, we used single-cell RNA sequencing to investigate BS differentiation in C4 maize (Zea mays L.) plants. Abaxial BS (abBS) cells of rank-2 intermediate veins specifically expressed three SWEET sucrose uniporters (SWEET13a, b, and c) and UmamiT amino acid efflux transporters. SWEET13a, b, c mRNAs were also detected in the Phloem parenchyma (PP). We show that maize has acquired a mechanism for Phloem Loading in which abBS cells provide the main route for apoplasmic sucrose transfer toward the Phloem. This putative route predominates in veins responsible for Phloem Loading (rank-2 intermediate), whereas rank-1 intermediate and major veins export sucrose from the PP adjacent to the sieve element companion cell complex, as in Arabidopsis thaliana. We surmise that abBS identity is subject to dorsoventral patterning and has components of PP identity. These observations provide insights into the unique transport-specific properties of abBS cells and support a modification to the canonical Phloem Loading pathway in maize.
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Phloem Loading via the abaxial bundle sheath cells in maize leaves
bioRxiv, 2020Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Wolf B Frommer, N Zoellner, Colin P S Kruse, Tobias Lautwein, K E Koehrer, Jiyun KimAbstract:ABSTRACT Leaves are asymmetric, with differential functionalization of abaxial and adaxial tissues. The bundle sheath (BS) surrounding the vasculature of the C3 crop barley is dorsoventrally differentiated into three domains: adaxial structural, lateral S-type, and abaxial L-type. S-type cells seem to transfer assimilates towards the Phloem. Here we used single-cell RNA sequencing to investigate BS differentiation in C4 maize. Abaxial BS (abBS) cells of rank-2 intermediate veins specifically expressed three SWEET sucrose uniporters (SWEET13a, b, and c) and UmamiT amino acid efflux transporters. SWEET13a, b, c were also identified in the Phloem parenchyma (PP). Thus maize acquired a unique mechanism for Phloem Loading in which abBS cells provide the main pathway for apoplasmic sucrose transfer towards the Phloem. This pathway predominates in veins responsible for Phloem Loading (rank-2 intermediate), while rank-1 intermediate and major veins export sucrose from the Phloem parenchyma (PP) adjacent to the sieve element companion cell (SE/CC) complex, as in Arabidopsis. We surmise that abBS identity is subject to dorsoventral patterning and has components of PP identity. These observations provide first insights into the unique transport-specific properties of abBS cells and support for a modification to the canonical Phloem Loading pathway of maize, which may be generalizable to other C4 monocots.
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impaired Phloem Loading in zmsweet13a b c sucrose transporter triple knock out mutants in zea mays
New Phytologist, 2018Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Marc Horschman, Si Nian Char, Jinliang Yang, Bing YangAbstract:Crop yield depends on efficient allocation of sucrose from leaves to seeds. In Arabidopsis, Phloem Loading is mediated by a combination of SWEET sucrose effluxers and subsequent uptake by SUT1/SUC2 sucrose/H+ symporters. ZmSUT1 is essential for carbon allocation in maize, but the relative contribution to apoplasmic Phloem Loading and retrieval of sucrose leaking from the translocation path is not known. Here we analysed the contribution of SWEETs to Phloem Loading in maize. We identified three leaf-expressed SWEET sucrose transporters as key components of apoplasmic Phloem Loading in Zea mays L. ZmSWEET13 paralogues (a, b, c) are among the most highly expressed genes in the leaf vasculature. Genome-edited triple knock-out mutants were severely stunted. Photosynthesis of mutants was impaired and leaves accumulated high levels of soluble sugars and starch. RNA-seq revealed profound transcriptional deregulation of genes associated with photosynthesis and carbohydrate metabolism. Genome-wide association study (GWAS) analyses may indicate that variability in ZmSWEET13s correlates with agronomical traits, especifically flowering time and leaf angle. This work provides support for cooperation of three ZmSWEET13s with ZmSUT1 in Phloem Loading in Z. mays.
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Impaired Phloem Loading in zmsweet13a,b,c sucrose transporter triple knock‐out mutants in Zea mays
The New phytologist, 2018Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Marc Horschman, Si Nian Char, Jinliang Yang, Bing Yang, Wolf B Frommer, Davide SossoAbstract:Crop yield depends on efficient allocation of sucrose from leaves to seeds. In Arabidopsis, Phloem Loading is mediated by a combination of SWEET sucrose effluxers and subsequent uptake by SUT1/SUC2 sucrose/H+ symporters. ZmSUT1 is essential for carbon allocation in maize, but the relative contribution to apoplasmic Phloem Loading and retrieval of sucrose leaking from the translocation path is not known. Here we analysed the contribution of SWEETs to Phloem Loading in maize. We identified three leaf-expressed SWEET sucrose transporters as key components of apoplasmic Phloem Loading in Zea mays L. ZmSWEET13 paralogues (a, b, c) are among the most highly expressed genes in the leaf vasculature. Genome-edited triple knock-out mutants were severely stunted. Photosynthesis of mutants was impaired and leaves accumulated high levels of soluble sugars and starch. RNA-seq revealed profound transcriptional deregulation of genes associated with photosynthesis and carbohydrate metabolism. Genome-wide association study (GWAS) analyses may indicate that variability in ZmSWEET13s correlates with agronomical traits, especifically flowering time and leaf angle. This work provides support for cooperation of three ZmSWEET13s with ZmSUT1 in Phloem Loading in Z. mays.
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impaired Phloem Loading in genome edited triple knock out mutants of sweet13 sucrose transporters
bioRxiv, 2017Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Marc Horschman, Si Nian Char, Jinliang Yang, Bing Yang, Davide Sosso, Wolf B FrommerAbstract:Crop yield depends on efficient allocation of sucrose from leaves to seeds. In Arabidopsis, Phloem Loading is mediated by a combination of SWEET sucrose effluxers and subsequent uptake by SUT1/SUC2 sucrose/H+ symporters. ZmSUT1 is essential for carbon allocation in maize, but the relative contribution to apoplasmic Phloem Loading and retrieval of sucrose leaking from the translocation path is not known. We therefor tested whether SWEETs are important for Phloem Loading in maize. Here we identified three leaf-expressed SWEET sucrose transporters as key components of apoplasmic Phloem Loading in Zea mays L. Notably, ZmSWEET13 paralogs (a, b, c) are among the highest expressed genes in the leaf vasculature. Genome-edited triple knock-out mutants are severely stunted. Photosynthesis of mutants was impaired and leaves accumulated starch and soluble sugars. RNA-seq revealed profound transcriptional deregulation of genes associated with the photosynthetic apparatus and carbohydrate metabolism. GWAS analyses may indicate that variability in ZmSWEET13s is correlated with agronomical traits, specifically flowering time and leaf angle. This work provides support for cooperation of three ZmSWEET13s with ZmSUT1 in Phloem Loading in Zea mays L. Our study highlights these three ZmSWEET13 sucrose transporters as possible candidates for the engineering of crop yield.
Wolf B Frommer - One of the best experts on this subject based on the ideXlab platform.
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evidence for Phloem Loading via the abaxial bundle sheath cells in maize leaves
The Plant Cell, 2021Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Wolf B Frommer, Colin P S Kruse, Tobias Lautwein, Nora Zollner, Karl Kohrer, Jiyun KimAbstract:Leaves are asymmetric, with different functions for adaxial and abaxial tissue. The bundle sheath (BS) of C3 barley (Hordeum vulgare) is dorsoventrally differentiated into three types of cells: adaxial structural, lateral S-type, and abaxial L-type BS cells. Based on plasmodesmatal connections between S-type cells and mestome sheath (parenchymatous cell layer below bundle sheath), S-type cells likely transfer assimilates toward the Phloem. Here, we used single-cell RNA sequencing to investigate BS differentiation in C4 maize (Zea mays L.) plants. Abaxial BS (abBS) cells of rank-2 intermediate veins specifically expressed three SWEET sucrose uniporters (SWEET13a, b, and c) and UmamiT amino acid efflux transporters. SWEET13a, b, c mRNAs were also detected in the Phloem parenchyma (PP). We show that maize has acquired a mechanism for Phloem Loading in which abBS cells provide the main route for apoplasmic sucrose transfer toward the Phloem. This putative route predominates in veins responsible for Phloem Loading (rank-2 intermediate), whereas rank-1 intermediate and major veins export sucrose from the PP adjacent to the sieve element companion cell complex, as in Arabidopsis thaliana. We surmise that abBS identity is subject to dorsoventral patterning and has components of PP identity. These observations provide insights into the unique transport-specific properties of abBS cells and support a modification to the canonical Phloem Loading pathway in maize.
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Phloem Loading via the abaxial bundle sheath cells in maize leaves
bioRxiv, 2020Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Wolf B Frommer, N Zoellner, Colin P S Kruse, Tobias Lautwein, K E Koehrer, Jiyun KimAbstract:ABSTRACT Leaves are asymmetric, with differential functionalization of abaxial and adaxial tissues. The bundle sheath (BS) surrounding the vasculature of the C3 crop barley is dorsoventrally differentiated into three domains: adaxial structural, lateral S-type, and abaxial L-type. S-type cells seem to transfer assimilates towards the Phloem. Here we used single-cell RNA sequencing to investigate BS differentiation in C4 maize. Abaxial BS (abBS) cells of rank-2 intermediate veins specifically expressed three SWEET sucrose uniporters (SWEET13a, b, and c) and UmamiT amino acid efflux transporters. SWEET13a, b, c were also identified in the Phloem parenchyma (PP). Thus maize acquired a unique mechanism for Phloem Loading in which abBS cells provide the main pathway for apoplasmic sucrose transfer towards the Phloem. This pathway predominates in veins responsible for Phloem Loading (rank-2 intermediate), while rank-1 intermediate and major veins export sucrose from the Phloem parenchyma (PP) adjacent to the sieve element companion cell (SE/CC) complex, as in Arabidopsis. We surmise that abBS identity is subject to dorsoventral patterning and has components of PP identity. These observations provide first insights into the unique transport-specific properties of abBS cells and support for a modification to the canonical Phloem Loading pathway of maize, which may be generalizable to other C4 monocots.
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Impaired Phloem Loading in zmsweet13a,b,c sucrose transporter triple knock‐out mutants in Zea mays
The New phytologist, 2018Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Marc Horschman, Si Nian Char, Jinliang Yang, Bing Yang, Wolf B Frommer, Davide SossoAbstract:Crop yield depends on efficient allocation of sucrose from leaves to seeds. In Arabidopsis, Phloem Loading is mediated by a combination of SWEET sucrose effluxers and subsequent uptake by SUT1/SUC2 sucrose/H+ symporters. ZmSUT1 is essential for carbon allocation in maize, but the relative contribution to apoplasmic Phloem Loading and retrieval of sucrose leaking from the translocation path is not known. Here we analysed the contribution of SWEETs to Phloem Loading in maize. We identified three leaf-expressed SWEET sucrose transporters as key components of apoplasmic Phloem Loading in Zea mays L. ZmSWEET13 paralogues (a, b, c) are among the most highly expressed genes in the leaf vasculature. Genome-edited triple knock-out mutants were severely stunted. Photosynthesis of mutants was impaired and leaves accumulated high levels of soluble sugars and starch. RNA-seq revealed profound transcriptional deregulation of genes associated with photosynthesis and carbohydrate metabolism. Genome-wide association study (GWAS) analyses may indicate that variability in ZmSWEET13s correlates with agronomical traits, especifically flowering time and leaf angle. This work provides support for cooperation of three ZmSWEET13s with ZmSUT1 in Phloem Loading in Z. mays.
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impaired Phloem Loading in genome edited triple knock out mutants of sweet13 sucrose transporters
bioRxiv, 2017Co-Authors: Margot Bezrutczyk, Thomas Hartwig, Marc Horschman, Si Nian Char, Jinliang Yang, Bing Yang, Davide Sosso, Wolf B FrommerAbstract:Crop yield depends on efficient allocation of sucrose from leaves to seeds. In Arabidopsis, Phloem Loading is mediated by a combination of SWEET sucrose effluxers and subsequent uptake by SUT1/SUC2 sucrose/H+ symporters. ZmSUT1 is essential for carbon allocation in maize, but the relative contribution to apoplasmic Phloem Loading and retrieval of sucrose leaking from the translocation path is not known. We therefor tested whether SWEETs are important for Phloem Loading in maize. Here we identified three leaf-expressed SWEET sucrose transporters as key components of apoplasmic Phloem Loading in Zea mays L. Notably, ZmSWEET13 paralogs (a, b, c) are among the highest expressed genes in the leaf vasculature. Genome-edited triple knock-out mutants are severely stunted. Photosynthesis of mutants was impaired and leaves accumulated starch and soluble sugars. RNA-seq revealed profound transcriptional deregulation of genes associated with the photosynthetic apparatus and carbohydrate metabolism. GWAS analyses may indicate that variability in ZmSWEET13s is correlated with agronomical traits, specifically flowering time and leaf angle. This work provides support for cooperation of three ZmSWEET13s with ZmSUT1 in Phloem Loading in Zea mays L. Our study highlights these three ZmSWEET13 sucrose transporters as possible candidates for the engineering of crop yield.
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Phloem Loading and unLoading of sugars and amino acids
Plant Cell and Environment, 2003Co-Authors: Sylvie Lalonde, Mechthild Tegeder, Wolf B Frommer, M Throneholst, John W. PatrickAbstract:In terrestrial higher plants, Phloem transport delivers most nutrients required for growth and storage processes. Some 90% of plant biomass, transported as sugars and amino nitrogen (N) compounds in a bulk flow of solution, is propelled though the Phloem by osmotically generated hydrostatic pressure differences between source (net nutrient export) and sink (net nutrient import) ends of Phloem paths. Source Loading and sink unLoading of sugars, amino N compounds and potassium largely account for Phloem sap osmotic concentrations and hence pressure differences. A symplasmic component is characteristic of most Loading and unLoading pathways which, in some circumstances, may be interrupted by an apoplasmic step. Raffinose series sugars appear to be loaded symplasmically. However, sucrose, and probably certain amino acids, are loaded into minor veins from source leaf apoplasms by proton symporters localized to plasma membranes of their sieve element/companion cell (se/cc) complexes. Sucrose transporters, with complementary kinetic properties, are conceived to function as membrane transporter complexes that respond to alterations in source/sink balance. In contrast, symplasmic unLoading is common for many sink types. Intervention of an apoplasmic step, distal from importing Phloem, is reserved for special situations. Effluxers that release sucrose and amino acids to the surrounding apoplasm in Phloem Loading and unLoading are yet to be cloned. The physiological behaviour of effluxers is consistent with facilitated membrane transport that can be energy coupled. Roles of sucrose and amino acid transporters in Phloem unLoading remain to be discovered along with mechanisms regulating symplasmic transport. The latter is hypothesized to exert significant control over Phloem unLoading and, in some circumstances, Phloem Loading.
James N Culver - One of the best experts on this subject based on the ideXlab platform.
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tobacco mosaic virus directed reprogramming of auxin indole acetic acid protein transcriptional responses enhances virus Phloem Loading
Proceedings of the National Academy of Sciences of the United States of America, 2016Co-Authors: Tamara D Collum, Meenu S Padmanabhan, Yicheng Hsieh, James N CulverAbstract:Vascular Phloem Loading has long been recognized as an essential step in the establishment of a systemic virus infection. In this study, an interaction between the replication protein of tobacco mosaic virus (TMV) and Phloem-specific auxin/indole acetic acid (Aux/IAA) transcriptional regulators was found to modulate virus Phloem Loading in an age-dependent manner. Promoter expression studies show that in mature tissues TMV 126/183-kDa-interacting Aux/IAAs predominantly express and accumulate within the nuclei of Phloem companion cells (CCs). Furthermore, CC Aux/IAA nuclear localization is disrupted upon infection with an interacting virus. In situ analysis of virus spread shows that the inability to disrupt Aux/IAA CC nuclear localization correlates with a reduced ability to load into the vascular tissue. Subsequent systemic movement assays also demonstrate that a virus capable of disrupting Aux/IAA localization is significantly more competitive at moving out of older plant tissues than a noninteracting virus. Similarly, CC expression and overaccumulation of a degradation-resistant Aux/IAA-interacting protein was found to inhibit TMV accumulation and Phloem Loading selectively in flowering plants. Transcriptional expression studies demonstrate a role for Aux/IAA-interacting proteins in the regulation of salicylic and jasmonic acid host defense responses as well as virus-specific movement factors, including pectin methylesterase, that are involved in regulating plasmodesmata size-exclusion limits and promoting virus cell-to-cell movement. Combined, these findings indicate that TMV directs the reprogramming of auxin-regulated gene expression within the vascular Phloem of mature tissues as a means to enhance Phloem Loading and systemic spread.
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Tobacco mosaic virus-directed reprogramming of auxin/indole acetic acid protein transcriptional responses enhances virus Phloem Loading
Proceedings of the National Academy of Sciences of the United States of America, 2016Co-Authors: Tamara D Collum, Meenu S Padmanabhan, Yicheng Hsieh, James N CulverAbstract:Vascular Phloem Loading has long been recognized as an essential step in the establishment of a systemic virus infection. In this study, an interaction between the replication protein of tobacco mosaic virus (TMV) and Phloem-specific auxin/indole acetic acid (Aux/IAA) transcriptional regulators was found to modulate virus Phloem Loading in an age-dependent manner. Promoter expression studies show that in mature tissues TMV 126/183-kDa-interacting Aux/IAAs predominantly express and accumulate within the nuclei of Phloem companion cells (CCs). Furthermore, CC Aux/IAA nuclear localization is disrupted upon infection with an interacting virus. In situ analysis of virus spread shows that the inability to disrupt Aux/IAA CC nuclear localization correlates with a reduced ability to load into the vascular tissue. Subsequent systemic movement assays also demonstrate that a virus capable of disrupting Aux/IAA localization is significantly more competitive at moving out of older plant tissues than a noninteracting virus. Similarly, CC expression and overaccumulation of a degradation-resistant Aux/IAA-interacting protein was found to inhibit TMV accumulation and Phloem Loading selectively in flowering plants. Transcriptional expression studies demonstrate a role for Aux/IAA-interacting proteins in the regulation of salicylic and jasmonic acid host defense responses as well as virus-specific movement factors, including pectin methylesterase, that are involved in regulating plasmodesmata size-exclusion limits and promoting virus cell-to-cell movement. Combined, these findings indicate that TMV directs the reprogramming of auxin-regulated gene expression within the vascular Phloem of mature tissues as a means to enhance Phloem Loading and systemic spread.