OsttaSBEIII expression alters granule size and increases starch levels and its degradability in Arabidopsis

The physicochemical properties of starches from different botanical origin, such as viscosity, gelatinization temperature, solubility and degradability depend on the amylose/amylopectin ratio and the length and frequency of the α-1,6-glycosidic bonds in amylopectin. These branches depend on the action of the starch branching enzymes (SBEs), which are highly structurally conserved in plants. We recently identified a novel gene from Ostreococcus tauri (OsttaSBEIII) which codes for a protein showing starch branching activity (OsttaSBEIII) and with a different structure than other known SBEs from plants, containing two in-tandem carbohydrate binding modules (CBM41-CBM48) at its N-terminus. OsttaSBEIII overexpression in A. thaliana plants resulted in a higher starch content and smaller granules with an increased degradability. OEOsttaSBE lines showed also an increase in the expression and activity of starch degradative enzymes and a higher content of glucose and inorganic phosphate, which suggests a remodeling of the granule structure in response to the expression of OsttaSBEIII. These results allow us to propose the use of OsttaSBEIII as a new strategy to obtain starches with greater degradability that would be useful for different biotechnological applications.