Activation tagging, an efficient tool for functional analysis of the rice genome.

Over the past 6 years, we have generated about 50,000 individual transgenic rice plants by an Agrobacterium-mediated transformation approach with the pER38 activation tagging vector. The vector contains tandemly arranged double 35S enhancers next to the right border of T-DNA. Expression analysis by reverse transcription-PCR indicates that the activation efficiency is high if the genes are located within 7 kb of the inserted double 35S enhancers. Comparative field phenotyping of part of the activation tagging and enhancer trapping populations in two generations (6,000 and 6,400 lines, respectively, in the T(0) generation, and 36,000 and 32,000 lines, respectively, in the T(1) generation) identified about four hundred dominant mutants. Characterization of a dominant mutant with a large leaf angle (M107) suggests that this mutant phenotype is caused by enhanced expression of CYP724B1/D11. The activation tagging pool described in this paper is a valuable alternative tool for functional analysis of the rice genome.