1. National Institute for Basic Biology, Okazaki 444-8585, Japan
2. Graduate School of Science, Tokyo Metropolitan University, Tokyo 192-0397, Japan
3. Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo 113-8657, Japan
4. Present address: Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.

Correspondence to: Hiro-Yuki Hirano⁴ Correspondence and requests for material should be addressed to H.-Y.H. (e-mail: Email: ahirano@mail.ecc.u-tokyo.ac.jp). Sequences of mPing and Ping have been deposited in the DDBJ under accession numbers AB087615 and AB087616, respectively.

Abstract

Transposable elements constitute a large portion of eukaryotic genomes and contribute to their evolution and diversification. Miniature inverted-repeat transposable elements (MITEs) constitute one of the main groups of transposable elements and are distributed ubiquitously in the genomes of plants and animals¹ such as maize^{2, 3, 4, 5}, rice³, Arabidopsis^{6, 7}, human⁸, insect^{9, 10} and nematode¹¹. Because active MITEs have not been identified, the transposition mechanism of MITEs and their accumulation in eukaryotic genomes remain poorly understood. Here we describe a new class of MITE, called miniature Ping (mPing), in the genome of Oryza sativa (rice). mPing elements are activated in cells derived from anther culture, where they are excised efficiently from original sites and reinserted into new loci. An mPing-associated Ping element, which has a putative PIF family⁵ transposase, is implicated in the recent proliferation of this MITE family in a subspecies of rice.