Abstract text: Plant growth and morphogenesis depend on the controlled remodeling of the primary cell wall, a dynamic structure whose mechanical properties are mainly regulated by homogalacturonan (HG)-type pectins. The length of HG chains is notably finely tuned by polygalacturonases (PGs), which have been reported to control growth in different species. Owing to its reduced number of genes encoding PGs, Physcomitrium patens was used as a model to study their roles in development. We biochemically characterized PpPG2 and PpPG3, two isoforms that differ in their structure, and showed that they both showed exo-acting activity determined by LC-MS/MS approach. In parallel, deletion mutants (pppg2, pppg3, pppg2/pppg3 double mutant) were generated and phenotyped. We showed that their cell wall composition, determined by neutral/acidic sugar composition and FTIR analysis was altered beyond pectins in mutants compared to wild-type. This had consequences on protonema development as the 2-dimensional growth of all three mutants was affected. Overall, we unequivocally showed that polygalacturonases are key actors regulating morphogenesis in Physcomitrium patens. This provides a novel framework combining genetics, biochemistry, and cell wall mechanics to better understand pectin remodeling during plant development.