title: Molecular and biochemical characterization of rice pectin methylesterase inhibitors (OsPMEIs).
abstract: Cell wall modifications such as partial degradation and depolymerization by cell wall hydrolases are normal cellular processes and are required for the functionalities of different cell types. Pectin, one of the major cell wall polysaccharides, is predominantly found in primary cell walls and middle lamellae and is subjected to in muro modification, primarily by cell wall-localized pectin methylesterases (PMEs). Molecular biochemical studies have demonstrated that enzymatic activities of PMEs are governed by multiple pectin methylesterase inhibitors (PMEIs), which consequently control the pectin methylesterification status. Although a few studies in Arabidopsis have shown the importance of this PMEI-mediated regulation in the biophysical properties of cell walls, little is known about the molecular physiological functions of rice PMEIs. We found 49 members of the PMEI family in the rice genome. Analysis of their transcript levels by quantitative real-time PCR and meta expression analysis showed that they are regulated spatially and temporally, as well as in response to diverse stresses. Quantification of cell wall-bound methylesters indicated that the degree of pectin methylesterification is developmentally regulated; in particular, higher PMEI activities were detected in cell wall proteins prepared from young leaves. Furthermore, an activity assay demonstrated that two recombinant OsPMEI proteins (OsPMEI8 and 12) were able to inhibit the enzymatic activity of a commercial PME protein. Subcellular localization indicated that OsPMEI8 is targeted to the middle lamella and OsPMEI12 is localized in the plasma membrane and nucleus. Taken together, our findings provide the first molecular and biochemical evidence for functional characterization of PMEIs in rice growth and development.
authors.affiliation: Graduate School of Biotechnology, Kyung Hee University, Yongin 446-701, South Korea.
authors.forename: Hong Phuong
authors.initials: HP
authors.lastname: Nguyen
authors.affiliation: Graduate School of Biotechnology, Kyung Hee University, Yongin 446-701, South Korea.
authors.forename: Ho Young
authors.initials: HY
authors.lastname: Jeong
authors.affiliation: Center for Eco-Friendly New Materials, Korea Research Institute of Chemical Technology, Daejeon 305-600, South Korea.
authors.forename: Hun
authors.initials: H
authors.lastname: Kim
authors.affiliation: Department of Herbal Crop Research, National Institute of Horticultural and Herbal Science, Rural Development Administration, Eumseong 27709, South Korea. Electronic address: ycpiano@korea.kr.
authors.forename: Young Chang
authors.initials: YC
authors.lastname: Kim
authors.affiliation: Graduate School of Biotechnology, Kyung Hee University, Yongin 446-701, South Korea; Department of Plant and Environmental New Resources, Kyung Hee University, Yongin 446-701, South Korea. Electronic address: chan521@khu.ac.kr.
authors.forename: Chanhui
authors.initials: C
authors.lastname: Lee
mesh_terms: D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D004791:Enzyme Inhibitors / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D012275:Oryza / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000096:biosynthesis / Q000235:genetics
chemical_list: D004791:Enzyme Inhibitors; D010940:Plant Proteins
keywords: Cell wall modifications; Pectin; Pectin methylesterase inhibitors; Pectin methylesterases; Plant cell walls; Rice