Abstract
Hydroxyproline-O-galactosyltransferase (GALT) initiates O-glycosylation of arabinogalactan-proteins (AGPs). We previously characterized GALT2 (At4g21060), and now report on functional characterization of GALT5 (At1g74800). GALT5 was identified using heterologous expression in Pichia and an in vitro GALT assay. Product characterization showed GALT5 specifically adds galactose to hydroxyproline in AGP protein backbones. Functions of GALT2 and GALT5 were elucidated by phenotypic analysis of single and double mutant plants. Allelic galt5 and galt2 mutants, and particularly galt2 galt5 double mutants, demonstrated lower GALT activities and reductions in β-Yariv-precipitated AGPs compared to wild type. Mutant plants showed pleiotropic growth and development phenotypes (defects in root hair growth, root elongation, pollen tube growth, flowering time, leaf development, silique length, and inflorescence growth), which were most severe in the double mutants. Conditional mutant phenotypes were also observed, including salt-hypersensitive root growth and root tip swelling as well as reduced inhibition of pollen tube growth and root growth in response to β-Yariv reagent. These mutants also phenocopy mutants for an AGP, SOS5, and two cell wall receptor-like kinases, FEI1 and FEI2, which exist in a genetic signaling pathway. In summary, GALT5 and GALT2 function as redundant GALTs that control AGP O-glycosylation, which is essential for normal growth and development.
Highlights
The fundamental processes that underpin plant growth and development depend crucially on the action and assembly of gene products designed to form the cell wall [1]
Given that glycosyltransferases containing a lectin domain are involved in catalyzing the first step of O-glycosylation of animal glycoprotein mucins, it was hypothesized that plant GALTs containing analogous lectin domains may function in initiating O-glycosylation of AGPs
The predicted protein structures and alignment of GALT2 and GALT5 are depicted in S1 Fig Both proteins are predicted to be type II membrane proteins with N-terminal transmembrane domains
Summary
The fundamental processes that underpin plant growth and development depend crucially on the action and assembly of gene products designed to form the cell wall [1]. Cell walls are composed of cellulose, hemicellulose, and pectin, along with protein and lignin [2]. Wall proteins have emerged as essential components because of their contribution to wall architecture and PLOS ONE | DOI:10.1371/journal.pone.0125624. GALT5 and 2 Function in AGP Glycosylation function [3]. Among the cell wall proteins, the hydroxyproline-rich glycoprotein (HRGP) superfamily constitutes the most abundant and diverse group of cell wall glycoproteins [4]. The HRGP superfamily is composed of a spectrum of molecules, ranging from lightly glycosylated proline-rich proteins to highly glycosylated arabinogalactan-proteins (AGPs) with the moderately glycosylated extensins in between these two extremes [5]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
