Chromosomal study of lettuce and its allied species (Lactuca spp., Asteraceae) by means of karyotype analysis and fluorescence in situ hybridization

摘要

The genus Lactuca belonging to the family Asteraceae is mainly distributed in temperate and warm regions of the Northern Hemisphere (Europe, Africa, Asia and America), and consists of about 100 species (Lebeda et al. 2004). One of the most important vegetable crops of the genus Lactuca is the cultivated lettuce (Lactuca sativa L.), and its wild relatives, especially the species L. serriola, L. saligna and L. virosa, are very important for the origin and genetic resources of the cultivated lettuce (Thompson et al. 1941; Lindqvist 1960b; Zohary 1991; De Vries 1997). In the last dozen years, relationships among the cultivated lettuce and its allied species have been studied using molecular techniques (Kesseli et al. 1991; Hill et al. 1996; Witsenboer et al. 1997; Koopman et al. 1998, 2001). These analyses clarify that the closest species of the cultivated lettuce is L. serriola.Cytological studies, karyotype analysis (Lindqvist 1960a; Haque and Godward 1985; Koopman and De Jong 1996) and chromosome banding (Koopman et al. 1993), have been demonstrated the relationships among lettuce and its closely related species. Lactuca sativa and L. serriola have almost the same chromosomal characteristics, while cytological features of L. saligna are slightly different from L. sativa/L. serriola, and that of L. virosa is significantly different from the other species. Recently, fluorescence in situ hybridization (FISH) techniques provide the phylogenetic information in closely related taxa, and FISH with ribosomal RNA genes and telomeric sequences has been widely utilized for karyotyping and studying chromosomal organization and evolution in many plant species (Li et al. 1997; Kulak et al. 2002; Hajdera et al. 2003; Seijo et al. 2004; Matoba et al. 2005). However, physical mapping of 5 S and 18 S rDNAs has been carried out only in the cultivated lettuce chromosomes (Matoba et al. 2001). Chromosomal studies using FISH techniques in the genus Lactuca are scarce in comparison with the sunflower, the genus Helianthus, which is one of the major crops of the same family (Asteraceae) as lettuce (Schrader et al. 1997; Cuéllar et al. 1999; Vanzela et al. 2002). Moreover, no data on the FISH with rRNA genes and telomere sequence is available in the wild relatives of the cultivated lettuce.The aim of this examination is to investigate the chromosomal distribution of 5 S and 18 S ribosomal RNA loci, and Arabidopsis-type (T3AG3) telomeric repeats using FISH technique, to promote the information on the chromosome organization and evolution of lettuce and its allied species. In addition, the correlation between chromosome organization and evolution of these species is discussed.