Academic journal article Genetics

Miniature Inverted-Repeat Transposable Elements of Stowaway Are Active in Potato

Academic journal article Genetics

Miniature Inverted-Repeat Transposable Elements of Stowaway Are Active in Potato

Article excerpt

ABSTRACT

Miniature inverted-repeat transposable elements (MITEs) are dispersed in large numbers within the genomes of eukaryotes although almost all are thought to be inactive. Plants have two major groups of such MITEs: Tourist and Stowaway. Mobile MITEs have been reported previously in rice but no active MITEs have been found in dicotyledons. Here, we provide evidence that Stowaway MITEs can be mobilized in the potato and that one of them causes a change of tuber skin color as an obvious phenotypic variation. In an original red-skinned potato clone, the gene encoding for a flavonoid 39,59-hydroxylase, which is involved in purple anthocyanin synthesis, has been inactivated by the insertion of a Stowaway MITE named dTstu1 within the first exon. However, dTstu1 is absent from this gene in a purple somaclonal variant that was obtained as a regenerated plant from a protoplast culture of the red-skinned potato. The color change was attributed to reversion of flavonoid 39,59-hydroxylase function by removal of dTstu1 from the gene. In this purple variant another specific transposition event has occurred involving a MITE closely related to dTstu1. Instead of being fossil elements, Stowaway MITEs, therefore, still have the ability to become active under particular conditions as represented by tissue culturing.

COLOR mutation or variegation of grain, flower petals, or fruit skin represents a suitable visual marker for the identification of genes for both pigment production and transposable elements (Clegg and Durbin 2000; Winkel-Shirley 2001; Kobayashi et al. 2004). Recent large-scale genome analyses have uncovered numerous transposable elements occupying large portions of eukaryotic genomes. Approximately 45% of the human genome is composed of sequences originating from .3 million copies of transposable elements (International Human Genome Sequencing Consortium 2001). Even in rice, a plant with a relatively small genome, 20% of the genomic sequence can be derived from transposable elements (Turcotte et al. 2001; Goff et al. 2002; Yu et al. 2002). Although almost all of these insertions are thought to be inactive, these elements are suggested to have influenced the evolution of genomes and individual genes. They can rearrange a genome through transposition, insertion, excision, chromosome breakage, or ectopic recombination (Bennetzen 2000). Moreover, some can contribute to the emergence of a novel gene by conveying a poly(A) signal, a transcription start site, a TATA box, a splicing site, or an intron (Oki et al. 2008).

Bioinformatic analyses using data of genome projects found a miniature inverted-repeat transposable element (MITE) (Bureau and Wessler 1992, 1994), the copy number of which reaches over thousands in a genome (Feschotte et al. 2002). Characteristically, a MITE is not .600 bp, does not contain any coding sequences, and has imperfect terminal inverted repeats (TIRs) at the end of the element and its target site is duplicated upon insertion. The majority of MITEs in plants are divided into two groups, Tourist and Stowaway, on the basis of the sequences of TIRs and their target sites, TAA and TA, respectively. Tourist MITEs are found in grasses while Stowaway is present not only in monocotyledonous but also in dicotyledonous plants (Bureau and Wessler 1992, 1994; Feschotte et al. 2002). Although huge numbers of MITEs of each family have been found since their discovery in silico, their dynamic features remain largely unknown. The first mobile MITE, mPing, was identified in rice and belongs to the Tourist family. Its movement was activated during long-term cell culture ( Jiang et al. 2003) and by anther culture (Kikuchi et al. 2003). When mPing was inserted into the gene for rice ubiquitin-related modifier-1 (Rurm1), its excision resulted in reversion of the mutable slender glume phenotype to wild type (Nakazaki et al. 2003). The identification of an active element made it possible to discover that the transposable elements Ping and Pong supplied the transposase acting on mPing (Yang et al. …

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