Stilbene synthase gene expression causes changes in flower colour and male sterility in tobacco

Summary Stilbene synthase genes (STS) have previously been used to enhance disease resistance in plants. In order to study the effects of modified STS expression patterns in plants, heterologous promoters were fused to an STS gene and the chimeric genes were transferred to tobacco. Very high constitutive expression of STS mediated by a duplicated upstream region of the 35S RNA promoter from CaMV affected secondary biosynthetic pathways. STS over‐expression caused altered flower pigmentation and male sterility, probably due to competition between the introduced STS and the endogenous chalcone synthase for the substrates 4‐coumaroyl CoA and malonyl CoA. Furthermore, tobacco plants with tapetum‐specific STS expression were male‐sterile. Thus, STS genes are promising tools in strategies for engineering altered flower colours and the development of a novel hybrid seed system.