Organization of a dispersed repeated DNA element in the Zamia genome

Abstract

Occurrence and genomic organization of dispersed elements containing ZpS1 satellite repeats have been investigated in a wide representation of species of the old plant genus Zamia (Zamiaceae, Cycadales). In Z. paucijuga, the ZpS1 repeat is organized as long satellite DNA arrays and as short arrays inserted into AT-rich dispersed elements. A comparative study by Southern analysis shows that these unusual dispersed elements containing the ZpS1 repeat are present with different organizations in all investigated Zamia species. In some species these elements are present with a low copy number, while in other species secondary amplification events, involving specific sequence clusters, appear to have generated characteristic dispersed elements in a high copy number. Among Zamia species, several groups share similar restriction patterns, as the Zamia loddigesii complex and the Caribbean species suggesting a general correlation between organization and genomic representation of the dispersed repeated sequence and the pattern of phyletic relationships in the genus. However, the finding of different patterns also among closely related species suggests a complex history of amplifications and losses of these dispersed repetitive elements that cannot be always easily traced through the phylogenetic reconstruction of this ancient plant group.

Chromosomal fission accounts for small-scale radiations in Zamia (Zamiaceae; Cycadales)

“…complex in Mexico (Vovides & Olivares, 1996; Stevenson, Moretti & Gaudio, 1998) show similar DNA sequence patterns [note that Z. loddigesii is now recognized as Z. prasina , for example, by Vovides & Olivares (1996)], whereas the banding pattern in Z. neurophyllidia D.W.Stev. differs from that of the other closely related basal Central American taxa (Cafasso et al ., 2009). Repeated sequences create multiple sequence homologies on chromosomes, which may cause alternative pairing arrangements and may, in turn, promote chromosomal fission.…”

“…There are only six cycad records in the C ‐value database (Ohri & Khoshoo, 1986; Leitch et al ., 2001; Murray, Leitch & Bennett, 2004). However, Cafasso et al . (2009) reported that all Zamia spp.…”

“…Products of chromosome fission pair with derived homologues at meiosis (Todd, 1970; Caputo et al ., 1996), but pericentric inversion often inhibits complete synapsis (Sturtevant, 1917; Kolnicki, 2000). Recently, Cafasso et al . (2009) have shown that patterns of repetitive DNA sequences dispersed across the genomes of Zamia spp.…”

“…analysed with both flow cytometry and quantitative dot blot analysis showed similar genomic DNA content to the standard Z. angustifolia Jacq., 1C = 12.05 pg (D. Cafasso, Università degli Studi di Napoli Federico II, Naples, personal communication). Although Cafasso et al . (2009) have yet to publish the C ‐values, their results provide strong evidence for chromosomal fission in these taxa.…”

Genome sizes for all genera of Cycadales

“…There are reports on nuclear DNA content determined using Feulgen microdensitometry in only four species of Cycadales (Ohri & Khoshoo 1986) but these deviate strongly from the results presented here. Cafasso et al. (2009) reported relative genome sizes in 32 Zamia species, all of which had an identical genome size (but see this article).…”