Hideyuki Matoba

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

In this study, in addition to the karyotype analysis, the chromosomal distributions of 5 S and 18 S rDNAs, and the Arabidopsis-type (T3AG3) telomeric sequences were detected by means of fluorescence in situ hybridization (FISH) to promote the information of chromosomal organization and evolution in the cultivated lettuce and its wild relatives, L. sativa, L. serriola, L. saligna and L. virosa. The karyotype analysis revealed the dissimilarity between L. virosa and the remaining species. In all four Lactuca species studied, one 5 S rDNA and two 18 S rDNA loci were detected. The simultaneous FISH of 5 S and 18 S rDNAs revealed that both rDNA loci of L. sativa, L. serriola and L. saligna were identical, however, that of L. virosa was different from the other species. These analyses indicate the closer relationships between L. sativa/L. serriola and L. saligna rather than L. virosa. Arabidopsis-type telomeric sequences were detected at both ends of their chromatids of all chromosomes not in the other regions. This observation suggests the lack of telomere-mediated chromosomal rearrangements among the Lactuca chromosomes.

Identification of parental genomes and genomic organization in Aster microcephalus var. ovatus

The karyotype of diploid Aster iinumae is morphologically similar to that of diploid Aster ageratoides var. ageratoides, however, its chromosome size is apparently smaller (S-type chromosomes versus L-type chromosomes, respectively). The hybrid origin of tetraploid Aster microcephalus var. ovatus (LS-type chromosomes) has previously been suggested by cytogenetics and chloroplast DNA (cp DNA) data. The cp DNA phylogeny also implies that the S-type chromosome is apomorphic, which means that genome size reduction occurred on the evolutionary way to A. iinumae. In this study, we have demonstrated that the chromosome size difference does not depend on the intensity of chromosome condensation but on the DNA content. The simultaneous genomic in situ hybridization (GISH) results show the similarity between S-type chromosomes of A. iinumae and A. microcephalus var. ovatus, and between L-type chromosomes of A. ageratoides and A. microcephalus var. ovatus, which provide additional evidence for A. microcephalus var. ovatus being a tetraploid amphidiploid produced by hybridization between S-type chromosomes and L-type chromosomes. The distribution patterns of Ty1-copia-like retrotransposons were similar in L- and S-type chromosomes. The copies of this retrotransposon dispersed uniformly on all chromosomes, and it is not yet apparent how the Ty1-copia-like retrotransposon affects the size difference between them.

Use of RAPD analysis to assess the threat of interspecific hybridization to the critically endangered Polemonium kiushianum in Japan

Polemonium kiushianum is a critically endangered species of which only eight populations exist in semi-natural grasslands of the Mt. Aso area of Kyushu, Japan. Habitat modification and the risk of hybridization with non-indigenous horticultural congeners, such as P. caeruleum subsp. caeruleum and P. caeruleum subsp. yezoense var. yezoense, pose increasing threats to P. kiushianum. To develop a DNA marker that distinguishes P. kiushianum from other Polemonium species, we performed random amplified polymorphic DNA (RAPD) analysis and selected an approximately 500-bp fragment generated by the OPB06 RAPD primer. In addition, we designed a primer pair, H11F/R, based on the nucleotide sequences of the fragments derived from P. caeruleum subsp. caeruleum and P. caeruleum subsp. yezoense var. yezoense. The results with the H11F/R primers indicated that most extant P. kiushianum plants in natural populations are not genetically contaminated by hybridization with non-indigenous horticultural species.