AtAGP18 is localized at the plasma membrane and functions in plant growth and development

Arabinogalactan-proteins (AGPs) are a family of highly glycosylated hydroxyproline-rich glycoproteins (HRGPs). AtAGP17, 18 and 19 comprise the lysine-rich classical AGP subfamily in Arabidopsis. Overexpression of GFP-AtAGP17/18/19 fusion proteins in Arabidopsis revealed localization of the fusion proteins on the plant cell surface of different organs. Subcellular localization of the fusion proteins at the plasma membrane was further determined by plasmolysis of leaf trichome cells. To elucidate AtAGP17/18/19 function(s), these AGPs were expressed without the green fluorescent protein (GFP) tag under the control of 35S cauliflower mosaic virus promoter. In contrast to AtAGP17/AtAGP19 overexpressors which showed phenotypes identical to wild-type plants, AtAGP18 overexpressors displayed several phenotypes distinct from wild-type plants. Specifically, these overexpressors had smaller rosettes and shorter stems and roots, produced more branches and had less viable seeds. Moreover, these AtAGP18 overexpressors exhibited similar phenotypes to tomato LeAGP-1 overexpressors, suggesting these two AGP genes may have similar function(s) in Arabidopsis and tomato.