Arabinogalactan proteins (AGPs) are a group of glycoproteins analogous to animal proteoglycans, which are found throughout the plant kingdom and play roles in plant growth and development. The protein backbone of AGPs is heavily O-glycosylated with arabinogalactan polysaccharides, with the glycan accounting for up to 90% of the total mass. The glycan contains mostly galactose and arabinose, but glucoronic acid and other less-abundant sugars like rhamnose, xylose and fucose are also found. Although AGPs are important for normal plant growth and are found throughout the plant in virtually all organs and tissues, their functions and synthesis are still poorly understood.
The aim of the research presented in the thesis was to characterize carbohydrate active enzymes involved in AGP biosynthesis and modification to gain insights into the biosynthesis of the glycoproteins in plants. Candidate glycosyltransferases and glycoside hydrolases were selected based on co-expression profiles from a transcriptomics analysis.
Reverse genetics approach on a novel glucuronosyltransferase involved in AGP biosynthesis has revealed that the enzyme activity is required for normal cell elongation in etiolated seedlings.
The enzymatic activity of a hydrolase from GH family 17 was investigated, without successful determination of the activity. Members of hydrolase family 43 appeared to be localized in the Golgi-apparatus, which is also the compartment for glycan biosynthesis. The localization of these glycoside hydrolases indicates likely involvement in the biosynthesis process of AGPs or other glycans rather than modification and degradation occurring in the extracellular space.