Insights into the Taxus baccata Karyotype Based on Conventional and Molecular Cytogenetic Analyses

The interest in Taxus species recently raised mainly for conservation concerns and biotechnological applications, the latter primarily associated with anticancer metabolites such as taxol. However, despite the commercial importance of the species, and in contrast with abundant studies on other Conifers, notably Pinaceae, cytogenetic information on Taxusis very limited and old.

In this work, karyotype analyses on English yew (Taxus baccata L., 2n =24) were performed by examining root tip meristematic cells derived from plant cuttings. Yew vegetative propagation was exploited to overcome seed deep dormancy and slow germination.

As in the other Gymnosperms, chromosome identification in yew is laborious, because of their similar size and morphology and of difficulties in obtaining good chromosome spreads.

However, by use of an image analysis software, the identification of 12 homologous pairs was achieved: most pairs resulted metacentric and submetacentric, but two, markedly shorter and acrocentric chromosome pairs could also be distinguished.

Multicolour fluorescence in situ hybridization (FISH) was successfully applied to metaphase spreads, using as probes a 5S rDNA sequence isolated from Taxus baccata, and a 18S rDNA sequence isolated in Populus. Both sequences were found to hybridize on the same submetacentric pair of chromosomes. Work is in progress to further describe T. baccata karyotype with additional FISH probes, including microsatellites sequences. This approach is expected not only to help characterizing each member of the chromosome set, but also to contribute to shed some light on yew genome structure and evolution, also in relation to more or less closely related species.