Karyotype of asparagus by physical mapping of 45S and 5S rDNA by FISH.

TLDR: Molecular cytogenetic and sequence analyses of bacterial artificial chromosomes (BACs) flanking M locus indicate that the BAC contain highly repetitive sequences that localize to centromeric and pericentromeric locations on all asparagus chromosomes.

Abstract: Garden asparagus (Asparagus officinalis L.) is an economically important plant with 2n = 2x = 20 chromosomes and a haploid genome size of 1323 Mb (Bennett and Leitch 2003). The karyotype of asparagus consists of five long (L), one medium (M) and four small (S) chromosomes (Löptien 1976). Plants of this dioecious species differ in producing either male or female flowers. The sexual dimorphism in asparagus is controlled by a region located on a pair of homomorphic sex chromosomes (chromosome L5) (Löptien 1979) termed the M locus (Flory 1932; Uno et al. 2002). Maleness is dominant with males normally heterogametic (Mm) and females homogametic (mm). Supermales (MM) can be produced from anther culture or from rarely occurring andromonoecious plants. The identification of chromosome L5 is important for studying sex chromosome evolution in asparagus. However, it was observed that the sex chromosome pair is homomorphic: X and Y chromosomes do not differ in morphology. Telgmann-Rauber et al. (2007) tried to clone the region determining sex in asparagus from its position in the genome. Molecular cytogenetic and sequence analyses of bacterial artificial chromosomes (BACs) flanking M locus indicate that the BAC contain highly repetitive sequences that localize to centromeric and pericentromeric locations on all asparagus chromosomes. However, the L5 chromosome could not be distinguished by BAC-FISH (Telgmann-Rauber et al. 2007). Recently, FISH has become a powerful and useful tool for the direct detection of specific DNA in genome. In this technique, ribosomal DNA genes (45S and 5S rDNA) are commonly used as markers for the physical mapping of plant chromosomes to analyse genomic organization (Nakayama et al. 2001; Lan et al. 2006; Grabowska-Joachimiak et al.