Interspecies comparison of the highly-repeated DNA of Australasian Luzula (Juncaceae)

Abstract

The woodrush genus Luzula is characterised by having holocentric chromosomes. DNA of nine related Australasian species shows similar satellite DNAs which re very similar in nucleotide sequence content and unit length. Differences between the repetitive DNAs are evident as either the presence or absence of particular restriction enzyme sites. Sequence variants have probably been introduced into the repeated DNA components of ancestral species and particular variants reamplified during the evolution of the genus. Sequence amplification appears to be restricted to sequences already present in the genome rather than the de novo generation of repeats. The evolution of highly-repeated DNA sequences dispersed throughout the holocentric chromosomes of Luzula thus appears to be very similar to that known in eukaryotes with the more normal monocentric chromosome organisation.

The cytogenetic architecture of the aphid genome

“…These results differ substantially from those observed in monocentric chromosomes, in which C‐heterochromatin typically occupies specific regions of all chromosomes, corresponding to centromeres and sometimes telomeres (Schweizer & Loidl, ). Research carried out in order to analyse heterochromatin localization in other taxa with holocentric chromosomes was in some cases unsuccessful (Collet & Westerman, ), but generally a telomeric and sometimes intercalary localization of C‐positive bands on the whole chromosome complement has been described (Kuznetzova & Sapunov, ; Papeschi, ; Grozeva & Nokkala, ; Haizel et al , ; Morielle‐Souza & Azeredo‐Oliveira, ; Hill et al , ). These data as a whole suggest that the preferential, and in some case the exclusive, localization of C‐heterochromatin on the X chromosome in aphids is not a consequence of their holocentrism, but must be considered a peculiar feature of aphid chromatin.…”

Cytogenetic and molecular characterization of a highly repeated DNA sequence in the peach potato aphid Myzus persicae

“…Studies carried out on satellite DNA sequences in organisms possessing holocentric chromosomes are scanty (Lagowsky et al 1973;Roth 1979;Collet and Westerman 1987;Naclerio et al 1992;Grenier et al 1996Grenier et al , 1997Castagnone Sereno et al 1998a, b). Only two highly repeated DNA sequences have been described in aphids to date: a 600 bp repeat unit that has been localized in the intercalary heterochromatin of Megoura viciae X chromosomes ) and a 169 bp tandem repeat that occurs at a subtelomeric location on all chromosomes of three species of the Myzus persicae complex (Spence et al 1998).…”

Distribution and molecular composition of heterochromatin in the holocentric chromosomes of the aphid Rhopalosiphum padi (Hemiptera: Aphididae)

“…Interestingly, R. padi showed large blocks of heterochromatin on all the chromosome complement, including large heterochromatic bands at both the telomeres of all the chromosomes. The rare researches carried out in order to analyse heterochromatin localization in other taxa possessing holocentric chromosomes, in some cases were unsuccessful (Collet and Westerman 1987), but generally a telomeric and sometimes intercalary localization of C positive bands on whole chromosome complement was described (Papeschi 1988;Grozeva and Nokkala 2003). This distribution substantially differs from what observed in monocentric chromosomes, where the heterochromatic regions typically occupy specific zones of all chromosomes, corresponding to centromeres (Schweizer and Loidl 1987).…”

“…At present, the few studies carried out on satellite DNA sequences in organisms possessing holocentric chromosomes were mostly focused on nematodes (Lagowsky et al 1973;Roth 1979;Collet and Westerman 1987;Naclerio et al 1992;Grenier et al 1996Grenier et al , 1997Castagnone-Sereno et al 1998a, b). In order to improve our knowledge about the structure of holocentric chromosomes, in the present paper we investigated the localization and the DNA composition of the heterochromatic bands in the holocentric chromosomes of the aphid Rhopalosiphum padi and isolated a satellite DNA that has been cloned, sequenced and localized by fluorescent in situ hybridization.…”