THE PLANT CELL, Vol 8, Issue 4 725-734, Copyright © 1996 by American Society of Plant Biologists
Autonomous Transposition of the Tobacco Retrotransposon Tto1 in Rice
H. Hirochika, H. Otsuki, M. Yoshikawa, Y. Otsuki, K. Sugimoto and S. Takeda
Department of Molecular Biology, National Institute of Agrobiological Resources, Tsukuba, Ibaraki 305, Japan
The complete nucleotide sequence of the tobacco retrotransposon Tto1, one
of the few active retrotransposons of plants, was determined. The sequence
analysis suggests that Tto1 carries all functions required for autonomous
transposition through reverse transcription. Gene organization and the
nature of the transcription product suggest that Tto1 uses a gene
expression mechanism different from those employed by retroviruses and most
retrotransposons to regulate Gag and Pol stoichiometry. Tto1 was introduced
into rice to study its autonomous transposition in heterologous hosts.
Transcription and transposition of Tto1 were observed in rice cells. To
probe the autonomous transposition through reverse transcription, a
modified Tto1 retrotransposon in which part of a reverse transcriptase gene
was replaced with an intron-containing hygromycin resistance gene was
constructed and introduced into rice cells. Loss of the intron was observed
only when intact Tto1 was cotransfected. These results indicate that Tto1
can transpose autonomously through reverse transcription and that the host
factors required for transposition are conserved among monocots (class
Magnoliopsida; rice) and dicots (class Liliopsida; tobacco), which diverged
~200 million years ago. These findings are discussed in relation to the
regulation and evolution of retrotransposons and the possible use of Tto1
as a molecular genetic tool.
