Enhancing the expression of starch synthase class IV results in increased levels of both transitory and long-term storage starch

Starch is an important renewable raw material with an increasing number of applications.Several attempts have been made to obtain plants that produce modified versions of starchor higher starch yield. Most of the approaches designed to increase the levels of starch havefocused on the increment of the amount of ADP-glucose or ATP available for starch biosyn-thesis. In this work, we show that the overexpression of starch synthase class IV (SSIV)increases the levels of starch accumulated in the leaves ofArabidopsisby 30%–40%. In addi-tion,SSIV-overexpressing lines display a higher rate of growth. The increase in starch contentas a consequence of enhancedSSIVexpression is also observed in long-term storage starchorgans such as potato tubers. Overexpression ofSSIVin potato leads to increased tuber starchcontent on a dry weight basis and to increased yield of starch production in terms of tons ofstarch⁄hectare. These results identify SSIV as one of the regulatory steps involved in the con-trol of the amount of starch accumulated in plastids. ; Comisión Interministerial de Ciencia y Tecnología de España y Fondo Europeo de Desarrollo Regional BIO2009-07040, BIO2007-63915 y PET2008-0106 ; Junta de Andalucía P09-CVI-4704