RAUBESON, LINDA A. Department of Biological Sciences, Central Washington University, Ellensburg, WA 98926. - Chloroplast DNA structural similarities shared by conifers and Gnetales: coincidence or common ancestry?
Chloroplast DNAs (cpDNAs) of conifers and Gnetales share aspects of
gene organization absent from angiosperm cpDNAs. The distribution of
these similarities is intriguing as it conflicts with the widely-held
view of Gnetales as the sister-group of angiosperms. However several
recent studies by other workers also have called this paradigm into
question. These other analyses have supported the gymnosperms as a
monophyletic clade or have supported, specifically, a Gnetales-conifer
clade. The cpDNA gene organization provides additional support for a
conifer-Gnetales relationship. One cpDNA similarity shared between
conifers and Gnetales (but lacking in angiosperms cpDNAs) is the
duplication (partial in the case of conifers; complete in Gnetales) of
the psbA gene. In addition, a duplication of the trnI
gene is found between trnH and psbA only in the cpDNAs
of conifers and Gnetales. These shared structural similarities appear
to be homologous and derived. Other possible structural similarities
are currently under investigation and may be discussed.
Key words: conifers, cpDNA, Gnetales, phylogeny, structural mutation