1. ¹MTT/BI Plant Genomics Laboratory, Institute of Biotechnology, Viikki Biocenter, University of Helsinki, Helsinki, Finland
2. ²Plant Genomics, Biotechnology and Food Research, MTT Agrifood Research Finland, Jokioinen, Finland

Correspondence: Professor AH Schulman, MTT/BI Plant Genomics Laboratory, Institute of Biotechnology, Viikki Biocenter, University of Helsinki, PO Box 56, Viikinkaari 4, FIN-00014 Helsinki, Finland. E-mail: alan.schulman@helsinki.fi

Received 12 May 2006; Revised 24 August 2006; Accepted 24 August 2006; Published online 20 September 2006.

Abstract

LTR (long terminal repeat) retrotransposons are the main components of higher plant genomic DNA. They have shaped their host genomes through insertional mutagenesis and by effects on genome size, gene expression and recombination. These Class I transposable elements are closely related to retroviruses such as the HIV by their structure and presumptive life cycle. However, the retrotransposon life cycle has been closely investigated in few systems. For retroviruses and retrotransposons, individual defective copies can parasitize the activity of functional ones. However, some LTR retrotransposon groups as a whole, such as large retrotransposon derivatives and terminal repeats in miniature, are non-autonomous even though their genomic insertion patterns remain polymorphic between organismal accessions. Here, we examine what is known of the retrotransposon life cycle in plants, and in that context discuss the role of parasitism and complementation between and within retrotransposon groups.