xylem

Rob Alba robalba at DOGWOOD.BOTANY.UGA.EDU
Fri Mar 15 12:48:25 EST 1996


	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



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