LAUSR

Starch is a glucose polymer synthesized by green plants for energy storage and is crucial for plant growth and reproduction. The biosynthesis of starch polysaccharides is mediated by members of the large starch synthase (SS) protein superfamily. Here, we showed that in cassava storage roots, soluble starch synthase II (MeSSII) plays an important role in starch biosynthesis and the formation of protein complexes with other starch biosynthetic enzymes by directly interacting with MeSSI, MeSBEII and MeISAII. The MeSSII-RNAi cassava lines showed increased amylose content and reduced intermediate chain of amylopectin (B1 type) biosynthesis in their storage roots, leading to altered starch physicochemical properties. Further gel permeation chromatography analysis of starch biosynthetic enzymes between the wild type and MeSSII-RNAi lines confirmed the key role of MeSSII in the organization of heteromeric starch synthetic protein complexes. The lack of MeSSII in cassava also reduced the binding capacity of MeSSI, MeSBEII, MeISAI, and MeISAII to starch granules. These findings shed light on the key components of the starch biosynthesis machinery in root crops.