Transposon Insertional Mutagenesis in Rice,

Transposon mutagenesis systems are being developed in rice to address gene functions using forward and reverse genetics strategies. Although the well-characterized maize (Zea mays) transposons seem an obvious choice to develop efficient transposon-tagging systems for gene knockouts and gene detection, heterologous transposons have not yet become a genome-wide system for saturation mutagenesis in rice (Oryza sativa). Our contributions as a multinational European initiative in developing heterologous transposon mutagenesis strategies for functional genomics in rice are described here. The endogenous retrotransposon Tos17 (Hirochika, 1997) has been effectively used to make knockouts of rice genes in a reverse genetics approach, but has a high frequency of untagged mutations, probably due to somaclonal variation associated with the tissue culture-based retrotransposition generation. Recent reports on transposition of Ac-Ds heterologous systems in rice have shown their activity and potential use as effective insertional mutagens (Izawa et al., 1997; Chin et al., 1999; Enoki et al., 1999; Nakagawa et al., 2000). The autonomous Ac has been shown to maintain a high rate of transposition, althoughDs elements might undergo silencing in later generations. The use of both systems in reverse genetic approaches has been reported to be potentially efficient.