Body of Abstract: Arabinogalactan-proteins (AGPs) are a family of hydroxyproline-rich glycoproteins present in plasma membranes, cell walls, and extracellular secretions of plants. AGPs play essential roles in the growth and development of plants. They are composed of ~10% protein and 90% sugar. The sugars on these proteins are added by enzymes called glycosyltransferases. The GT 31 family of glycosyltransferases (GALTs) includes several GALT enzymes which add the first sugar, a galactose to hydroxyproline residues in the AGP backbone. Eight GALT enzymes named GALT2-GALT9 are found to have this activity in Arabidopsis thaliana. Genetic ‘knock-out” single mutants for each of the GALT genes in Arabidopsis show subtle abnormal phenotypic changes. More severe phenotypic changes were observed in genetic ‘knock-out” of multiple GALT genes. Despite the extensive knowledge of AGPs, their mechanism of action remains unknown. In this research, two approaches; RNA sequencing and genetic suppressor screening are being used to elucidate the mechanism of action of AGPs. RNA-seq analysis helps to understand what genes are activated ("turned on") or down-regulated ("turned off") to make AGPs play their roles in plants. Genetic suppressor screening on the other hand, gives an understanding of how AGPs work by identifying molecules and biochemical pathways associated with them. This knowledge can be applied in agriculture to improve crop production through genetic engineering and make the production of Arabinogalactan-proteins available in a large scale to food and pharmaceutical industries that make use of AGPs.