Cytogenetics of the permanent translocation heterozygote rhoeo spathacea var. variegata. Implications for complex chromosome rearrangements in rhoeo

Abstract

The chromosomal morphology, arrangement of AT- and GC-rich chromatin, 5S and 45S rDNA, NORs, and centromere behaviour during somatic interphase and during meiotic prophase I were studied for the first time in the variegated ring-forming Rhoeo variety – R. spathacea var. variegata. Fluorescence in situ hybridization (FISH) together with differential base-specific fluorescence revealed the existence of the highly conserved karyotype in Rhoeo. It was shown that the two existing ring-forming varieties -R. spathacea variegata and R. discolor (common Rhoeo variety) share essentially the same arrangement of the studied cytogenetic landmarks within the chromosomal arms, together with the spread of the GC-rich DNA sequences (including rDNA) across all the twelve pericentromeres. They both also exhibit the same profound trend for centromere clustering in soma- and germ-line. The obtained results together with the existing literature served as a basis to summarize the cytogenetic knowledge on the karyotype structure in Rhoeo. A series of argumentations pointing to the whole-arm translocations (WATs) as the rearrangements leading to meiotic catenation in Rhoeo was presented. A possible role of ancient inversions in the evolution of the PTH system in Rhoeo was discussed. © 2011 Taylor and Francis Group, LLC.