The systematics of Sphaerocardamum (Cruciferae) is addressed to test the monophyly of the genus and to establish its phylogenetic relationships within the family and among its species. Chloroplast ndhF and trnL intron data are used to establish family level relationships and as an initial test of monophyly. Morphological and DNA sequence data sources (including pistillata intron, ITS, and cp trnL intron/trnL-F spacer) are integrated from a denser taxon sample as a further test of monophyly, to establish species level phylogenetic hypotheses, and to aid in species delimitation. In addition, aspects of morphological character evolution are studied in this phylogenetic context. Preliminary results identify a monophyletic Sphaerocardamum nested within a primarily Mexican clade that includes members of Halimolobos, Mancoa, and Pennellia.Systematics of Sphaerocardamum (Brassicaceae).
*C. Donovan Bailey†, Robert A. Price‡, and Jeff J. Doyle†. †LH Bailey Hortorium, Cornell Univ., Ithaca, NY 14853. ‡Dept. of Botany, Univ. of Georgia, Athens, GA 30602.
MBE paper 1999.
We report the
potential phylogenetic utility of DNA sequence data from the last 700 base
pairs of a ca. one kilobase intron of the MADS-box gene pistillata
from a sampling of Sphaerocardamum species and other Brassicaceae.
These results are compared with nrDNA ITS and the chloroplast trnL
intron for the same taxa to demonstrate the potential phylogenetic utility
of this pistillata intron and to identify potentially historically
independent sequences for an ongoing study of relationships within Sphaerocardamum.
Analyses of the DNA sequence data for Brassicaceae indicated that pairwise
divergences and potentially informative characters were higher in the pistillata
intron (0.6-30.8%, 284 characters) and ITS (0-24%, 92 characters) than
in the chloroplast trnL intron (0-4.2%, 16 characters). A
comparison of Sphaerocardamum sequences identified low divergences
and numbers of informative characters for trnL intron (0-2.4%, 1
character) and nrDNA ITS (0-2.5%, 2 characters), and substantially more
variation among the pistillata sequences (0.15-3.7%, 15 substitutions and
4 indel characters). Phylogenetic analyses of these pistillata
sequences fully resolve ingroup relationships without character conflict.
Results of pistillata PCR amplifications from a broader dicot sample
showed that some primers may be useful in amplifying orthologous pistillata
sequences. Ultimately this pistillata intron may be a valuable
source of phylogenetic characters at lower taxonomic levels.
AIBS 1997
Sphaerocardamum Schauer is a small genus (ca. 8 spp.) of narrowly distributed Mexican Brassicaceae that exhibits a range of morphological variation in some key taxonomic characters that are important in the family as a whole. As part of the systematic study of Sphaerocardamum, DNA sequence data have been sampled from the chloroplast and nuclear genomes in order to identify historically independent sequences with levels of variation appropriate for resolving relationships both within Sphaerocardamum and among Sphaerocardamum and related genera. This initial survey indicated that the trnL intron of the chloroplast genome contains sufficient variation for both of these purposes, while nrDNA ITS lacks sufficient variation at the species level. Using primers designed for the conserved regions of the well characterized MADS-box gene family of Arabidopsis, we amplified the gene pistillata from Sphaerocardamum and several Brassicaceae in search of a more variable nuclear sequence. This single copy gene in Arabidopsis possesses a large (1000 bp) intron around which we have designed sequencing primers. Sequences from our sampled taxa indicate that the 5’ end of the intron is considerably more variable, in both nucleotide substitution and length variation, than is the nrDNA ITS and will provide characters at the lower taxonomic levels. In addition, the intron in Sphaerocardamum and some other taxa begins with a two base-pair microsatellite-like repeat, (TC) , which may be useful in population level studies.A comparison of the potential phylogentic utility of an intron of the MADS-box gene pistillata to the nrDNA ITS and the chloroplast trnL intron in Sphaerocardamum Schauer (Brassicaceae).
*C. Donovan Bailey and Jeff J. Doyle. L. H. Bailey Hortorium
462 Mann Library, Cornell University, Ithaca, NY 14853.
Systematic Botany
DONOVAN BAILEY and JEFF J. DOYLE
L.H. Bailey Hortorium, 462 Mann
Library
Cornell University, Ithaca NY
14853-4301
TADASHI KAJITA, TOMOYUKI NEMOTO,
and HIROYOSHI OHASHI
Biological Institute, Graduate School
of Tohoku University
Sendai, Miyagi 980, Japan
In a previous extensive survey of the Leguminosae it was discovered that most but not all members of the papilionoid tribe Desmodieae lacked the intron for the chloroplast gene rpl2 and partially or completely lacked the open reading frame ORF184. We report the results of a more intensive survey of Desmodieae for loss of these sequences which includes all 26 genera recognized in the most recent comprehensive taxonomic treatment of the tribe. Methods included slot blot hybridization using gene- or intron-specific probes, polymerase chain reaction amplification across the rpl2 intron region, and DNA sequencing across the rpl2 intron/exon boundary in representatives of selected genera (Desmodium, Lepedeza, and Phylacium). The rpl2 intron was found to be absent from all genera of the largest subtribe, Desmodiinae, and absent from the three core members of Lespedezinae. It was found to be present in both members of Bryinae and in the other two Lespedezinae genera (Neocollettia and Phylacium). In contrast to the rpl2 intron, the pattern of ORF184 loss in Desmodiinae and Lespedezinae was extremely complex and difficult to interpret from slot blots. Within subtribes Desmodiinae and Lespedezinae, ORF184 showed hybridization results consistent either with partial deletion or extensive sequence divergence. Bryinae members showed little evidence of loss. In agreement with the distribution of the rpl2 intron, Bryinae have been considered to have affinities outside Desmodiinae, while both Phylacium and Neocollettia are anomalous within Lespedezinae. Thus the rpl2 intron loss may represent a synapomorphy for a “core” Desmodieae.