Visual selection in rice: a strategy for the efficient identification of transgenic calli accumulating transgene products.

Fluorescent proteins such as green fluorescent protein (GFP) allow direct visualization of transformed cells without the need for exogenous substrates. Furthermore, visual selection using GFP is a powerful tool that can be used to isolate transformed cells without antibiotic or herbicide pressure and can be applied to transformation systems in plants hypersensitive to these agents. Moreover, we propose that visual selection enables isolation of calli in which the gene of interest is expressed to a high level, by selecting calli in which a strong GFP signal is observed. However, until now, the efficiency of clonal propagation using visual selection has been lower than that in antibiotic selection because of the technical difficulties involved in the isolation and clonal propagation of transformed calli with conventional transformation frequencies. We have succeeded in improving the efficiency of clonal propagation by the use of a rice cultivar that exhibits high competency for Agrobacterium-mediated transformation.