In planta mobilization of mPing and its putative autonomous element Pong in rice by hydrostatic pressurization

Abstract

The miniature Ping (mPing) is a recently discovered endogenous miniature inverted repeat transposable element (MITE) in rice, which can be mobilized by tissue culture or irradiation. It is reported here that mPing, together with one of its putative transposase-encoding partners, Pong, was efficiently mobilized in somatic cells of intact rice plants of two distinct cultivars derived from germinating seeds subjected to high hydrostatic pressure, whereas the other autonomous element of mPing, Ping, remained static in the plants studied. mPing excision was detected in several plants of both cultivars in the treated generation (P0), which were selected based on their novel phenotypes. Southern blot analysis and transposon-display assay on selfed progenies (P1 generation) of two selected P0 plants, one from each of the cultivars, revealed polymorphic banding patterns consistent with mobilization of mPing and Pong. Various mPing excisions and de novo insertions, as detected by element-bracketing, locus-specific PCR assays, occurred in the different P1 plants of both cultivars. Pong excision at one locus for each cultivar was also detected by using a Pong internal primer together with locus-specific flanking primers in the P1 plants. In contrast to the pressurized plants, immobility of both mPing and Pong in control plants, and the absence of within-cultivar heterozygosity at the analysed loci were verified by Southern blotting and/or locus-assay. Sequencing at 18 mPing empty donor sites isolated from the pressurized plants indicated properties characteristic of the element excision. Sequence-based mapping of 10 identified mPing de novo insertions from P1 progenies of pressurized plants indicated that all were in unique or low-copy regions, conforming with the targeting propensity of mPing. No evidence for further mPing activity was detected in the P2 plants tested. In spite of the high activity of mPing and Pong in the pressurized plants, amplified fragment length polymorphism (AFLP) analysis denoted their general genomic stability, and several potentially active retrotransposons also remained largely immobile. Further investigation showed that the same hydrostatic pressure treatments also caused mobilization of mPing in the standard laboratory cultivar for japonica rice, Nipponbare. Thus, a simple and robust approach for in planta MITE-mobilization in rice has been established by using high hydrostatic pressure treatment, which may be useful as an alternative for gene-tagging in this important crop plant.

DNA Transposons and the Evolution of Eukaryotic Genomes

“…mPing was identified as the first actively transposing MITE in any organism (84,103). mPing transposition has been observed in vivo in response to various stress conditions and correlated with the coactivation of Pong, a distantly related autonomous transposon of the PIF/Harbinger superfamily (84,116,172). Recently, it was also shown that Pong and Ping-encoded proteins are necessary and sufficient to mobilize mPing in transgenic Arabidopsis plants (198c).…”

Evolutionary Genomics of Miniature Inverted-Repeat Transposable Elements (MITEs) in Plants

“…Four prominent exceptions are marked in red predicted that the mPing family was active since it has many identical elements in rice genome (Jiang et al 2003). Their transposability was experimentally verified using long-term cell culture (Jiang et al 2003), anther culture (Kikuchi et al 2003), and hybridization (Shan et al 2005) and hydrostatic pressurization (Lin et al 2006). Recently, another MITE family (mGings) was found to actively transpose in rice seedlings and plantlets regenerated from anther-derived calli (Dong et al 2012).…”

Editor’s Choice: Crop Genome Plasticity and Its Relevance to Food and Feed Safety of Genetically Engineered Breeding Stacks

“…Some elements insert at random, some insert near genes, and some insert preferentially into centromeric or heterochromatic areas (Schnable et al, 2009). Transposition of mobile elements can be activated by mutagenesis (Anderson, 1948;McClintock, 1950;Gowda et al, 2011), transformation (Wu et al, 2009), tissue culture (Peschke et al, 1987;Hirochika et al, 1996;Jiang et al, 2003;Barret et al, 2006;Gowda et al, 2011;Smith et al, 2012), wide hybridization (Liu and Wendel, 2000;Wang et al, 2010;Zou et al, 2011), and stress (Lin et al, 2006;Gowda et al, 2011).…”