As the world's third-largest food crop, cassava accumulates large amounts of starch in its storage roots, providing a major source of food energy for nearly 700 million people in tropical and subtropical regions. Better understanding its regulation of starch metabolism not only increases our knowledge of the source-sink partitioning mechanism but also improves yield in root crops at large.

Using the first cassava T-DNA insertion mutant storage root delay (srd), we revealed that the key gene causing the retarded plant and storage root growth was the α-glucan, water dikinase 1 (GWD1) gene. Repression of the GWD1 expression resulted in starch excess phenotypes with reduced photosynthetic capacity and decreased levels of soluble saccharides in their leaves. These leaves contained starch granules having greatly increased amylose content and type C semi-crystalline structures with increased short chains that suggested storage starch. The study also confirmed that starch degradation in cassava is catalyzed by β-amylase in collaboration with GWD1 function by phosphorylation of starch. These results suggest that GWD1 regulates transient starch morphogenesis and storage root growth by decreasing photo-assimilation partitioning from the source to the sink and by starch mobilization in root crops. These germplasms also provide new source for leaf utilization.

The study was mainly conducted by Dr. Wenzhi Zhou and collaborated with Profs. Wilhelm Gruissem and Samuel Zeeman from ETH Zurich. The article “Alpha-Glucan, Water Dikinase 1 Affects Starch Metabolism and Storage Root Growth in Cassava (Manihot esculenta Crantz)” was published by Scientific Reports recently. The work was supported by projects from the Chinese Academy of Science, Ministry of Science and Technology, Ministry of Agriculture, National Science Foundation of China, Sino-Swiss Science and Technology Cooperation and National Key laboratory of Plant Molecular Genetics.