A new perspective on starch phosphorylation in planta

The global modified starch market was valued at USD 11.8 billion in 2021 and is expected to increase at a compound annual growth rate (CAGR) of 5.3% from 2022 to 2030 (www.grandviewresearch.com). The demand for modified starch for various food and non-food products is driven by a growing world population. As a result, it is already becoming increasingly important to adapt the properties of starch within the plant to the corresponding needs through targeted genetic manipulations to safe energy, costs and the environment. To date, phosphoesterification is the only known naturally occurring covalent starch modification mediated by the α-glucan, water dikinase (GWD) and phosphoglucan, water dikinase (PWD). The phosphate groups introduced at the OH-C6 or OH-C3 position in the double helical structures of amylopectin have a significant impact on the physico-chemical properties of starch So far, up to triple phosphorylated chains have been detected (Ritte et al 2002; Hejazi et al 2009)., but it is unclear whether there is a specific pattern that is universal for all starch-related dikinases, mutants and starch sources. We established a workflow to address this issue in detail using ³³P-β-[ATP] radioactive labelling assays and MS, MS/MS analyses as well (Compart et al 2023; 2024). Furthermore, the question arises how a large protein as GWD (155kDa) binds to double helices with a length a little more than 6 nm (DP18). Therefore, we used alphafold2 to predict the action of the GWD on the starch granule surface.