A Powerful Tool for Efficient Recurrent Selection: Positively and Negatively Selectable Male-Sterile Rice

Recurrent selection is a powerful breeding method of maize: populations are improved by shuffling the many types and highly diverse genomes of maize through its allogamous mode of reproduction. To use the same selection method in an autogamous crop like rice, breeders are required to do several and continuous artificial crossings, furthermore recurrent selection is difficult to perform on a large scale. To circumvent these issues, we propose a novel method based on the development and application of a negatively and positively selectable, single-locus dominant transgenic male sterility. This method is will allow for an efficient recurrent selection in autogamous crop species (Tanaka 2010). The male sterility trait is used only during the breeding procedure and will be removed from the final products (‘null segregant’) since male-sterile individuals cannot self-pollinate to produce inbred lines. Currently at the NARO institute of crop science and NIAS, the development of transgenic rice for an efficient recurrent selection is in progress. We have developed anther-specific expression promoters from a comprehensive study using the expression profile database RiceXPro. The developed promoters were confirmed to be effective in producing dominant male-sterile individuals. Herbicide tolerance genes can be used as positively selectable markers. Fluorescent protein expressed under the gluteline promoter accumulate in the endosperm (Qu and Takaiwa 2006) and can be efficiently used as either positive or negative selectable, visible  markers. We are now in the prototype development stage and will present our study and envisioned future applications.