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Gum Arabic that is Enzymatically Modified with Arabidopsis Beta-Glucuronosyltransferase Can Make Smaller and more Stable Oil-in-Water Emulsions

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材料科学与工程（中英文A版） 2015年第1期5卷 69-77页

作者： adiphol dilokpim.l Naomi Geshi Department of Plant and Environmental Sciences University of Copenhagen Frederiksberg C 1871 Denmark Fungal Physiology CBS-KNA WFungal Biodiversity Centre Utrecht 3584 CT The Netherlands.

A plant glycosyltransferase was utilized to modify the properties of gum arabic as an oil-in-water emulsifier. We previously reported that recombinant beta-glucuronosyltransferase (AtGlcAT14A) from Arabidopsis thaliana produced in Pichia pastoris possesses glucuronosyltransferase activity to transfer glucuronic acid (GlcA) from UDP-GlcA to beta-1,3-galactan main chain and beta-1,6-galactan side chains of type II arabinogalactan. In this paper, we report that AtGlcAT14A can also transfer GlcA from UDP-GlcA to gum arabic at the optimal pH value of 5 in the absence of dicationic ion. In the modified gum Arabic, GlcA was primarily incorporated into the beta-1,6-galactans. The oil-in-water emulsions created by the modified gum arabic were smaller, less flocculated and threefold more stable than that produced by the unmodified gum arabic. It is conceivable that the additional GlcA on the surface of gum arabic prevents flocculation by increasing surface electrostatic repulsion, which leads to more stable oil-in-water emulsions. Our study implicates the structure-function relationship and provides a potential method for the enzyme-based manipulation of gum arabic.

关键词：阿拉伯树胶葡萄糖醛酸酶促改性拟南芥稳定阿拉伯半乳聚糖水乳液油包水乳状液

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Complex Regulation of Prolyl-4-Hydroxylases Impacts Root Hair Expansion

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Molecular Plant 2015年第5期8卷 734-746页

作者： Silvia M. Velasauez Martiniano M. Ricardi Christian Peter Poulsen Ai Oikawa adiphol dilokpim.l Adnan Halim Silvina Mangano Silvina Paola Denita Juarez Eliana Marzol Juan D. Salgado Salter Javier Gloazzo Dorosz Cecilia Borassi Svenning Rune Moller Rafael Buono Yukiko Ohsawa Ken Matsuoka Marisa S. Otegui Henrik V. Scheller Naomi Geshi Bent larsen Petersen Norberto D. lusem Jose M. Estevez Instituto de Fisiologfa Biologia Molecular y Neurociencias (IFIBYNE-CONICET) Facultad de Ciencias Exactas y Naturales Universidad de Buenos AiresBuenos Aires C1428EGA Argentina VKR Research Centre Department of Plant and Environmental Sciences University of Copenhagen DK-1871 Frededksberg C Denmark Joint BioEnergy Institute Feedstocks Division Lawrence Berkeley National Laboratory 5885 Hollis Street Emeryville CA 94608 USA Copenhagen Center for Glycomios Department of Cellular and Molecular Faculty of Health and Medical Sciences University of CopenhagenDK-2200 Copenhagen N Denmark Department of Botany University of Wisconsin Madison WI 53706 USA RIKEN Plant Science Center Tsurumi-ku Yokohama 230-0045 Japan laboratory of Plant Nutrition Faculty of Agriculture Kyushu University Hakozaki 6-10-1 Higashi-ku Fukuoka 812-8581 Japan Departamento de Fisiologia Biologia Molecular y Celular Facultad de Ciencias Exactas y Naturales Universidad de Buenos Aires Buenos Aires C1428EGAArgentina These authors contributed equally to the article. Present address: Fungal Physiology CBS-KNAW Fungal Biodiversity Center Uppsalalaan 8 Utrecht 3584 CT The Netherlands Present address: The Danish Stem Cell Center The Panum Institute Blegdamsvej 3B DK-2200 Copenhagen Denmark

Root hairs are single cells that develop by tip growth, a process shared with pollen tubes, axons, and fungal hyphae. However, structural plant cell walls impose constraints to accomplish tip growth. In addition to polysaccharides, plant cell walls are composed of hydroxyproline-rich glycoproteins （HRGPs）, which include several groups of O-glycoproteins, including extensins （EXTs）. Proline hydroxylation, an early post-translational modification （PTM） of HRGPs catalyzed by prolyl 4-hydroxylases （P4Hs）, defines their subsequent O-glycosylation sites. In this work, our genetic analyses prove that P4H5, and to a lesser extent P4H2 and P4H13, are pivotal for root hair tip growth. Second, we demonstrate that P4H5 has in vitro preferred specificity for EXT substrates rather than for other HRGPs. Third, by P4H promoter and protein swapping approaches, we show that P4H2 and P4H13 have interchangeable functions but cannot replace P4H5. These three P4Hs are shown to be targeted to the secretory pathway, where P4H5 forms dimers with P4H2 and P4H13. Finally, we explore the impact of deficient proline hydroxylation on the cell wall architec- ture. Taken together, our results support a model in which correct peptidyl-proline hydroxylation on EXTs, and possibly in other HRGPs, is required for proper cell wall self-assembly and hence root hair elongation in Arabidopsis thaliana.

关键词： enzymology cell expansion cell walls protein targeting proline hydroxylation root hairs

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