Characterization of waxy starches from CRISPR-Cas9 edited potato plants, the loss of GBSS1 influences the phosphate con-tent inside the starch granule

The granule-bound starch synthase is responsible for amylose biosynthesis. This enzyme is ac-tive when physically associated with starch granules where it represents up to 95% of starch-bound proteins. gbss1 mutants of Solanum tuberosum, cv Desiree were recently generated by CRIPR/Cas9-driven gene edition. Here, we investigated the impact of the modulation of GBSS1 contents on the starch-bound proteome and the resulting amylopectin structure. The total protein content in knock-out mutants was decreased by 50 %, which indicate a compensation by the other proteins since GBSS1 represent 85 % of the total protein content. This compensation was mainly due to the increase of starch-bound SS2 (starch synthase 2) and GWD (glucan water dikinase). These changes were accompanied by an increase of the phosphate content. Taken to-gether, these data reveal that GBSS1 loss is compensated by the association of other starch met-abolic enzymes with starch granules, with a strong increase of GWD, leading to modified amy-lopectin structure.