MUSTANG is a novel family of domesticated transposase genes ...
MUSTANG is a novel family of domesticated transposase genes ... MUSTANG is a novel family of domesticated transposase genes ...
Abstract While transposons have traditionally been viewed as genomic parasites or “junk DNA”, the discovery of transposon-derived host genes has fuelled an ongoing debate over the evolutionary role of transposons. In particular, while mobility-related open reading frames have been known to acquire host functions, the contribution of these types of events to the evolution of genes is not well known. Here we report that genome-wide searches for Mutator transposase-derived host genes in Arabidopsis thaliana (Columbia-0) and Oryza sativa ssp. japonica (cv. Nipponbare) (domesticated rice) identified 121 sequences, including the taxonomically-conserved MUSTANG1. Syntenic MUSTANG1 orthologs in such varied plant species as rice, poplar, Arabidopsis, and Medicago truncatula appear to be under purifying selection. However, despite the evidence of this pathway of gene evolution, MUSTANG1 belongs to one of only two Mutator- like gene families with members in both monocotyledonous and dicotyledonous plants, suggesting that Mutator-like elements seldom evolve into taxonomically widespread host genes. Downloaded from http://mbe.oxfordjournals.org/ by guest on July 15, 2013
Introduction Mobile elements have traditionally been viewed as “junk DNA” or as genomic parasites (Doolittle and Sapienza 1980; Orgel and Crick 1980). However, reports of transposon-derived genes contributing to cellular processes (Agrawal, Eastman, and Schatz 1998; Mi et al. 2000; Hudson, Lisch, and Quail 2003) have indicated that such genetic elements may influence the evolution of their host by providing a source of novel coding capacity. Other lines of evidence such as sequence analysis and conservation studies, also support this view (International Human Genome Sequencing Constorium 2001; Hammer, Strehl, and Hagemann 2005; Zdobnov et al. 2005). This, in turn, has spurred controversy concerning the extent to which transposable elements contribute to host evolution (Hurst and Werren 2001). In plants, the only transposon-like genes with known host functions, far-red impaired response protein 1 (FAR1), far-red elongated hypocotyl 3 (FHY3) and the FAR1 related sequences (FRS), are related to the family of DNA transposons called Mutator-like elements (MULEs) (Hudson, Lisch, and Quail 2003; Lin and Wang 2004). MULEs are DNA transposons, which move via a “cut-and-paste” mechanism (Lisch 2002). The mudrA gene of autonomous elements encodes the transposase MURA that is required for MULE mobility (Lisch et al. 1999). Though most MULEs are bounded by terminal-inverted repeats (TIRs) of ~200 bp in length, some MULEs lack terminal symmetry and are termed non-TIR MULEs (Yu, Wright, and Bureau 2000). In maize, MURA binds specifically to the terminal sequences of MULEs (Benito and Walbot 1997). This association between the transposase and the terminal sequences appears necessary for excision of the element to occur, as it is in other DNA transposons (Steiniger- White, Rayment, and Reznikoff 2004). Upon insertion of the MULE into the genome, 9-11 bp target site duplications (TSDs) are created (Bennetzen 1996). Downloaded from http://mbe.oxfordjournals.org/ by guest on July 15, 2013
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Abstract<br />
While transposons have traditionally been viewed as genomic parasites or “junk DNA”, the<br />
d<strong>is</strong>covery <strong>of</strong> transposon-derived host <strong>genes</strong> has fuelled an ongoing debate over the evolutionary<br />
role <strong>of</strong> transposons. In particular, while mobility-related open reading frames have been known<br />
to acquire host functions, the contribution <strong>of</strong> these types <strong>of</strong> events to the evolution <strong>of</strong> <strong>genes</strong> <strong>is</strong> not<br />
well known. Here we report that genome-wide searches for Mutator <strong>transposase</strong>-derived host<br />
<strong>genes</strong> in Arabidops<strong>is</strong> thaliana (Columbia-0) and Oryza sativa ssp. japonica (cv. Nipponbare)<br />
(<strong>domesticated</strong> rice) identified 121 sequences, including the taxonomically-conserved<br />
<strong>MUSTANG</strong>1. Syntenic <strong>MUSTANG</strong>1 orthologs in such varied plant species as rice, poplar,<br />
Arabidops<strong>is</strong>, and Medicago truncatula appear to be under purifying selection. However, despite<br />
the evidence <strong>of</strong> th<strong>is</strong> pathway <strong>of</strong> gene evolution, <strong>MUSTANG</strong>1 belongs to one <strong>of</strong> only two Mutator-<br />
like gene families with members in both monocotyledonous and dicotyledonous plants,<br />
suggesting that Mutator-like elements seldom evolve into taxonomically widespread host <strong>genes</strong>.<br />
Downloaded from<br />
http://mbe.oxfordjournals.org/<br />
by guest on July 15, 2013
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