Rice Genetics IV - IRRI books - International Rice Research Institute

eau and Wessler 1992, 1994), rice (Bureau and Wessler 1994a,b, Bureau et al 1996),green pepper (Pozueta-Romero et al 1996), and Arabidopsis (Casacuberta et al 1998,Surzycki and Belknap 1999, Kapitonov and Jurka 1999, Le et al 2000), MITEs arealso in several animal genomes including Caenorhabditis elegans (Oosumi et al 1995b,Surzycki and Belknap 2000), insects (Tu 1997), fish (Izsvak et al 1999), and humans(Morgan 1995, Oosumi et al 1995a).A MITE family is loosely defined as a group of related elements (usually with>70% sequence identity, frequently >85%) whose amplification/transposition has beencatalyzed by a transposase that is encoded by a class 2 autonomous element. Figure 1shows the hypothetical position of MITEs in a traditional transposable element family.This hierarchy is called hypothetical because strains harboring active MITEs havenot yet been described. Although computer analysis of genomic sequence has identifiedputative autonomous elements in Arabidopsis (Feschotte and Mouches 2000, Leet al 2000) and C. elegans (Oosumi et al 1995b), no genetic relationship between aMITE family and an active autonomous element has been established.Although all TE classes are found in higher plants, both LINEs and SINEs areless prevalent in plant than in mammalian genomes (discussed in Wessler et al 1995).Instead, LTR retrotransposons and MITEs appear to predominate in plants. LTRretrotransposons are the most abundant element in many plant genomes. The discoverythat the vast intergenic regions of maize are composed largely of LTRretrotransposons led to the hypothesis that these elements preferentially target otherretrotransposons for insertion (San Miguel et al 1996). A similar insertion site preferencewas reported for BARE-1 of barley (Suoniemi et al 1997) and RIRE1 of wild rice(Noma et al 1997, Kumekawa et al 1999).MITEs appear to be the most prevalent element associated with the genic regionsof higher plants, especially those in the grass clade (Bureau et al 1996, Hu et al 2000,Tarchini et al 2000). An actual preference for genic regions has been established fortwo maize MITEs: Hbr (Zhang et al 2000) and mPIF (N. Jiang, X. Zhang, andAutonomousTransposaseNonautonomous