With regards to Jim Perry's comments about the placement of
Psilotum on evolutionary trees, I thought recent work in
Schneider-Poetsch's lab might be of interest to some of you (Kolukisaoglu
et al., J Mol Evol, 1995 vol. 41). Kolukisaoglu et al. are using a
conserved region of phytochrome genes obtained from many "higher" and
"lower" plants to investigate the evolutionary divergence of
phytochrome gene families in both "higher" and "lower" land plants.
Their molecular (DNA) phylogenetic data support two interesting
hypotheses: 1) most non-angiosperms have small phytochrome gene families
(1-2 members) while the few angiosperms which have been well
characterized appear to have much larger gene families (3-11 members; 5
different, expressed, phytochrome genes have been isolated from both A.
thaliana and Tomato). Thus, to date, it appears that angiosperm
phytochrome gene families are larger and more complex than
their non-angiosperm counterparts. 2) Perhaps more relevant to this
discussion, Kolukisaoglu's data also suggest that the clade containing
Selaginella, Equisetum and mosses is basal to the clade which
contains Psilotum. It appears (when using phytochrome DNA sequences)
Psilotum is more closely related to the 4 ferns used in their study. Thus,
it appears they have obtained further evidence in support of
the hypothesis that Psilotum is not a close relative of the first vascular
plants.
Does anyone know where Psilotum "falls out" when one genereates
similar evolutionary trees with Cytochrome Oxidase, NADH dehydrogenase,
and/or Rubisco sequences?
Rob Alba
Dept of Botany
The University of Georgia
