Abstract text: Polarized tip growth is a key morphological adaption that facilitated land plant terrestrialization, and arabinogalactan proteins (AGPs) are central regulators of this process. However, how glycosylation modulates AGP function during tip growth remains poorly understood. Here, we show that the AGP SLEEPING BEAUTY (SB) is required for cell wall integrity during protonemal tip growth in the moss Physcomitrium patens, a function that is conserved in the distantly related vascular plant Arabidopsis thaliana. Loss-of-function SB allele exhibits tip growth defects associated with cellulose microfibril organization and compromised cell wall integrity. Using a hypoglycosylated SB variant, we demonstrate that glycosylation of Pro55, Pro92, and Pro94 within a highly intrinsically disordered region is required for proper SB secretion and vacuolar trafficking; loss of these modifications results in pronounced inhibition of tip growth. We propose that the intrinsically disordered domain of SB might function as a cell wall-associated scaffold that facilitates cellulose microfibril biosynthesis or assembly, thereby promoting polarized tip growth.