Overexpressing an universal stress protein gene IbUSP17 increases starch content without yield penalty in sweetpotato

• The role of USPs in regulating starch biosynthesis is for the first time reported. • IbUSP17 increases starch content and amylopectin proportion without yield penalty in sweetpotato. • IbUSP17 increases starch content by enhancing the expression of genes and the activities of enzymes involved in starch biosynthesis. The universal stress proteins (USPs) play important roles not only in abiotic stress tolerance but also in plant growth and development. However, the role of USPs in regulating starch biosynthesis has not been reported. In this research, the IbUSP17 gene was isolated from a sweetpotato line H283 with high starch content. The IbUSP17 protein was localized in the nucleus. IbUSP17 were highly expressed in the lines with high starch content and during rapid thickening and starch accumulation period of storage roots. Overexpressing IbUSP17 increased storage root starch content, especially amylopectin proportion, without storage root yield penalty in sweetpotato. Overexpression of IbUSP17 up-regulated the genes involved in starch biosynthesis and increased the activities of enzymes related to amylopectin biosynthesis. The contents of components related to starch biosynthesis were also increased in the IbUSP17 -overexpressing plants. Silencing this gene produced opposite effects. These results suggest that overexpression of IbUSP17 increases starch content through up-regulating the genes involved in starch biosynthesis and increasing the activities of enzymes related to starch biosynthesis, especially amylopectin biosynthesis. It is the first time to reveal the role of the USP gene in starch biosynthesis. This gene is expected to be used to increase starch yield and improve starch quality in sweetpotato.