Heterologous expression of two Arabidopsis starch dikinases in potato

Starch phosphate esters influence physiochemical properties of starch granules that are essential both for starch metabolism and industrial use of starches. To modify properties of potato starch and understand the effect of starch phosphorylation on starch metabolism in storage starch, the starch dikinases from Arabidopsis thaliana, glucan water dikinase 2 and 3 (AtGWD2 and AtGWD3), were heterologously expressed in potato tubers (Solanum tuberosum) from two genetic backgrounds: the amylose-containing clone Kardal and the amylose-free mutant amf. Modified starches showed altered granule morphology, but no significant changes in starch phosphate content were observed. Genes involved in starch metabolism did not show altered expression in the transgenic lines relatively to the control; however, sucrose synthase 4 (SUSY4) was upregulated in transgenic tubers with AtGWD2 expression. Taken together, these results demonstrated that expression of AtGWD2 and AtGWD3 are not suitable for engineering starch with a high phosphate content in potato tubers but can provide new insights in the process of starch phosphorylation in the amyloplast