Noncoding sequences from the slowly evolving chloroplast inverted repeat in addition to rbcL data do not support gnetalean affinities of angiosperms |
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Authors: | Goremykin V; Bobrova V; Pahnke J; Troitsky A; Antonov A; Martin W |
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Institution: | A. N. Belozersky Institute of Physicochemical Biology, Moscow State University. |
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Abstract: | We developed PCR primers against highly conserved regions of the rRNA
operon located within the inverted repeat of the chloroplast genome and
used these to amplify the region spanning from the 3' terminus of the 23S
rRNA gene to the 5' terminus of the 5S rRNA gene. The sequence of this
roughly 500-bp region, which includes the 4.5S rRNA gene and two
chloroplast intergenic transcribed spacer regions (cpITS2 and cpITS3), was
determined from 20 angiosperms, 7 gymnosperms, and 16 ferns (21,700 bp).
Sequences for the large subunit of ribulose bisphosphate
carboxylase/oxygenase (rbcL) from the same or confamilial genera were
analyzed in both separate and combined data sets. Due to the low
substitution rate in the inverted repeat region, noncoding sequences in the
cpITS region are not saturated with substitutions, in contrast to
synonymous sites in rbcL, which are shown to evolve roughly six times
faster than noncoding cpITS sequences. Several length polymorphisms with
very clear phylogenetic distributions were detected in the data set.
Results of phylogenetic analyses provide very strong bootstrap support for
monophyly of both spermatophytes and angiosperms. No support for a sister
group relationship between Gnetales and angiosperms in either cpITS or rbcL
data was found. Rather, weak bootstrap support for monophyly of gymnosperms
studied and for a basal position for the aquatic angiosperm Nymphaea among
angiosperms studied was observed. Noncoding sequences from the inverted
repeat region of chloroplast DNA appear suitable for study of land plant
evolution.
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