Spatial Configuration of Transposable ElementAcTermini Affects Their Ability to Induce Chromosomal Breakage in Maize  

Abstract

Composite or closely linked maize (Zea mays) Ac/Ds transposable elements can induce chromosome breakage, but the precise configurations of Ac/Ds elements that can lead to chromosome breakage are not completely defined. Here, we determined the structures and chromosome breakage properties of 15 maize p1 alleles: each allele contains a fixed fractured Ac (fAc) element and a closely linked full-length Ac at various flanking sites. Our results show that pairs of Ac/fAc elements in which the termini of different elements are in direct or reverse orientation can induce chromosome breakage. By contrast, no chromosome breakage is observed with alleles containing pairs of Ac/fAc elements in which the external termini of the paired elements can function as a macrotransposon. Among the structures that can lead to chromosome breaks, breakage frequency is inversely correlated with the distance between the interacting Ac/Ds termini. These results provide new insight into the mechanism of transposition-induced chromosome breakage, which is one outcome of the chromosome-restructuring ability of alternative transposition events.

Genome Rearrangements in Maize Induced by Alternative Transposition of ReversedAc/DsTermini

“…Each resulting chromatid would have a deletion flanking either the 59 Ac or 39 fAc ends (Figure 4). Insertion of the Ac/fAc termini in the opposite orientation would lead to formation of a chromatid bridge and chromosome breakage, as previously proposed (Huang and Dooner 2008;Yu et al 2010). This model fits previous observations, including those that: (1) Ac/Ds elements exhibit a pronounced preference for local transposition; (2) the Ac element from the standard p1-vv allele often inserts into the sister chromatid (Greenblatt and Brink 1962); (3) the maize p1 gene promoter and exon 1 sequences are preferred sites for Ac insertion (Athma et al 1992), and this region is located within the Ac/fAc intertransposon segment in the P1-rr11 and P1-rr910 alleles.…”

“…Reversed Ds ends in very close proximity exhibit reduced alternative transposition in maize: Previously we reported that alleles containing pairs of reverseoriented Ac/Ds ends can cause chromosome breakage, and chromosome-breakage frequency is inversely proportional to the distance between the element termini (Yu et al 2010). The previous study examined pairs of Ac/Ds elements separated by distances ranging from 0.8 to 13 kb.…”

“…The maize alleles P1-rr11, P1-rr910, and P1-ovov454 were isolated and described previously (Zhang and Peterson 2004;Zhang et al 2009;Yu et al 2010). Plants in which the P1-rr11, P1-rr910, or P1-ovov454 alleles were heterozygous with an allele for colorless kernel pericarp (p1-ww or p1-wr) were crossed by pollen from plants of genotype p1, r1-m3::Ds.…”

“…Kernels of mature ears were examined and the numbers of colorless sectors were used as an index to the chromosome-breakage frequency. The chromosome-breakage frequency grading is evaluated according to Yu et al (2010).…”

“…In this configuration, reversed-ends transposition can induce a variety of chromosome rearrangements, including deletions, inversions, translocations, and ITS rearrangements (Zhang and Peterson 2004;Zhang et al 2009). In addition, this reversed-ends configuration can induce chromosome breakage (Huang and Dooner 2008;Yu et al 2010).…”