Jittery, a Mutator Distant Relative with a Paradoxical Mobile Behavior: Excision without Reinsertion

Abstract

The unstable mutation bz-m039 arose in a maize (Zea mays) stock that originated from a plant infected with barley stripe mosaic virus. The instability of the mutation is caused by a 3.9-kb mobile element that has been named Jittery (Jit). Jit has terminal inverted repeats (TIRs) of 181 bp, causes a 9-bp direct duplication of the target site, and appears to excise autonomously. It is predicted to encode a single 709-amino acid protein, JITA, which is distantly related to the MURA transposase protein of the Mutator system but is more closely related to the MURA protein of Mutator-like elements (MULEs) from Arabidopsis thaliana and rice (Oryza sativa). Like MULEs, Jit resembles Mutator in the length of the element's TIRs, the size of the target site duplication, and in the makeup of its transposase but differs from the autonomous element Mutator-Don Robertson in that it encodes a single protein. Jit also differs from Mutator elements in the high frequency with which it excises to produce germinal revertants and in its copy number in the maize genome: Jit-like TIRs are present at low copy number in all maize lines and teosinte accessions examined, and JITA sequences occur in only a few maize inbreds. However, Jit cannot be considered a bona fide transposon in its present host line because it does not leave footprints upon excision and does not reinsert in the genome. These unusual mobile element properties are discussed in light of the structure and gene organization of Jit and related elements.

Transposition of the rice miniature inverted repeat transposable element mPing in Arabidopsis thaliana

“…Here, we demonstrate that, regardless of the source of transposase tested, excision of mPing is usually precise. As such, this is only the second characterized plant transposon with a preference for precise excision (22). Our data also indicate that mPing, unlike most (but not all) DNA transposons, does not have a preference for insertion into sites linked to the donor.…”

The Transposable Element Landscape of the Model LegumeLotus japonicus

“…While previous studies identified two major groups of plant MULEs (MuDR and Jittery-like) (Lisch 2002;Xu et al 2004), we were surprised to find a third lineage in L. japonicus ( Figure 3A). In addition to MuDRlike (27 elements) and Jittery-like (24 elements) MULEs, the third lineage is most closely related to a small group of recently discovered fungal MULEs called Hop from Fusarium oxysporum (Chalvet et al 2003) and to a MULE element from Magnaporthe grisea than to any other plant element.…”

“…A new MULE lineage: Virtually all MULEs identified to date in plants belong to one of two groups: MUDR and Jittery-like (Yu et al 2000;Lisch 2002;Xu et al 2004). It was therefore surprising to find a third group of MULEs in L. japonicus that is more closely related to the fungal element Hop (Chalvet et al 2003) than to MUDR or Jittery-like MULEs ( Figure 3A).…”

Sequence diversity and copy number variation of Mutator-like transposases in wheat

“…Most of MULE transposases in plants were reported to exhibit higher similarity to the transposase of Jittery than to MURA (Walbot and Rudenko 2002;Xu et al 2004) and the Jittery clade also included the largest numbers of MULEs in T. aestivum. Many MULE transposases belonging to the Jittery clade are probably also present in T. urartu.…”

“…Homologous sequences from Triticum and Aegilops were searched in the TIGR Wheat Genome Database using BLASTn and tBLASTx (Altschul et al 1997). Two other Mutator-related elements, Trap (Comelli et al 1999) and Jittery (Xu et al 2004), have been identified in maize. Mutator-like transposases were divided into four classes in sugarcane, rice and Arabidopsis (Rossi et al 2004).…”