Genome rearrangements and gene regulation in higher plants

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The Japanese morning glory (lpomoea nil) displaying blue flowers has an extensive history of genetic and physiological studies. A number of its spontaneous mutants related to the flower colors have been isolated, and several lines of evidence indicate that an En/Spm-related transposable element Tpn 1 and its relatives are major sources of these spontaneous mutations. Indeed, many flower color mutants including white flower mutants are caused by integration of Tpn 1-related non-autonomous elements. One of them is a purple-mutable allele conferring purple flowers with blue spots and sectors. The purple gene was identified to encode a vacuolar Na^+/H^+ exchanger that is responsible for increase vacuolar pH for blue flower coloration.The mutable flaked line of the common morning glory (Ipomoea purpurea) displays white flowers with colored flakes, and the flaked mutation is caused by the insertion of a transposable element Tip 100 into the CHS-D gene for anthocyanin biosynthesis. The 3.9 kb Tip 100 element belongs to the AciDs family. We examined whether Tip 100 is an autonOmous element capable of transposition in heterologous tobacco plants. The intact Tip 100 element was able to excise from its original position in an introduced vector and to reinsert into new sites in the tobacco genome, whereas its internal deletion derivative was not. Based on these results, we concluded that Tip 100 is an autonomous element.The modification of targeted chromosomal genes through homologous recombination is a powerful tool of reverse genetics for characterizing gene functions. We are trying to develop a procedure for targeted gene disruption by homologous recombination in the single locus gene Waxy of rice. A transgenic rice plant having a targeted gene disrupted by a transgene was isolated, which appears to be a heterozygote with only one copy of the integrated transgene in its genome.