Here, we provide an isobaric tag for relative and absolute quantitation (iTRAQ)-based quantitative proteomic dataset of the moss Physcomitrium patens smg1 knockout line. The kinase SMG1 is one of the key components of the NMD system in many organisms, including plants. Several lines with a deleted SMG1 in a land Physcomitrium patens subsp. patens (“Gransden 2004”, Frieburg) were produced by James P. B. Lloyd [doi.org/10.1111/tpj.12329]. One of these lines, SMG1 KO mutant line 2, was used for this study. Protonemata of WT and mutant lines were grown in200 ml liquid BCD medium supplemented with 5 mM ammonium tartrate (BCDAT) during a 16-h photoperiod at 250C for 8 days [https://doi.org/10.1101/pdb.prot5136]. All experiments were performed in three biological replicates.