Chromosome Maps of Trilliaceae: II. A Study of the Genome Composition in Polyploid Species of the Genus Trillium by Fluorescence Nucleotide Base-Specific Staining of Heterochromatic Chromosome Regions

Abstract

Chromosome banding with nucleotide base-specific fluorochromes chromomycin A3 (CMA) and Hoechst 33258 (H33258) was used to study the karyotypes and to construct cytological maps for diploid Trillium camschatcense (2n = 10), tetraploid T. tschonoskii (2n = 20), hexaploid T. rhombifolium (2n = 30), and a triploid T. camschatcense x T. tschonoskii hybrid (T. x hagae, 2n = 15). With H33258, species- and genome-specific patterns with numerous AT-rich heterochromatin bands were obtained for each of the four forms; CMA revealed a few small, mostly telomeric GC-rich bands. In T. tschonoskii, the two subgenomes were similar to each other and differed from the T. camschatcense genome; on this evidence, the species was considered to be a segmental allotetraploid. In T. x hagae, one T. camschatcense and both T. tschonoskii subgenomes were identified. The subgenomes of T. rhombifolium only partly corresponded to the T. camschatcense and T. tschonoskii genomes, in contrast to the morphologically identical Japanese species T. hagae. This was assumed to indicate that allohexaploids T. rhombifolium and T. hagae originated independently at different times; i.e., their origin is polyphyletic. Based on the chromosome maps, a new nomenclature was proposed for the Trillium genomes examined: K1K1 for T. camschatcense, T1T1T2T2 for T. tschonoskii, T1T1T2T2 for T. x hagae, and K1RK1RT1RT1RT2RT2R for T. rhombifolium.