Ribosomal External and Internal Transcribed Spacers: Combined Use in the Phylogenetic Analysis of Medicago (Leguminosae)

Abstract

We have estimated the potential phylogenetic utility of the ribosomal external transcribed spacer (ETS) from the nuclear ribosomal region. The ETS was sequenced from 13 annual Medicago (Fabaceae) species upstream a highly conserved motive which was found among many different organisms. In the genus Medicago, the ETS was found to evolve 1.5 times faster than the internal transcribed spacer and to be 1.5 times more informative. Reduced ribosomal maturation process constraints on ETS are proposed to explain the different evolutionary rates between the two spacers. Maximal phylogenetic resolution and support was obtained when the two spacers were analyzed together. No incongruence between the two spacers was found and ETS appears to be a valuable source of information for solidifying ITS plant phylogeny. The phylogeny obtained in Medicago suggests that none of the three subsections included in the study is monophyletic.

Characterization of the rRNA Locus of Pfiesteria piscicida and Development of Standard and Quantitative PCR-Based Detection Assays Targeted to the Nontranscribed Spacer

“…Based on the P. piscicida rDNA sequence described above, we designed PCR primers targeting those regions (NTS, internal transcribed spacer 1 [ITS1], and ITS2) considered to be the most variable within the rRNA gene cluster (4,12). The NTS regions of various isolates of P. piscicida were amplified in a PCR with primers PP12 and PP5.…”

“…For example, the high conservation of the SSU among closely related species, subspecies, and strains may represent a drawback for the accurate intraspecific identification of environmental isolates. Therefore, alternative detection assays that target intergenic regions such as the nontranscribed spacer (NTS), a region known in other Alveolata to have a higher intra-and interspecies variability than the SSU (4,12), have been successfully developed. These include PCR assays for species-and strain-specific detection of parasites of the genus Perkinsus (15,18,35,49,50).…”

Molecular phylogenetic approach for studying life-history evolution: the ambiguous example of the genus Medicago L.

“…ETS and ITS sequences of nuclear rDNA were analysed by combining the two data sets (see Baldwin et al (1995) for a review for the use of ITS in phylogenetic reconstruction, and Bena et al (1998a) for the use of ETS). Phylogenetic trees were constructed by Fitch parsimony methods (Fitch 1971).…”

Evidence for convergent evolution among phylogenetically distant rare species of Tetratheca (Elaeocarpaceae, formerly Tremandraceae) from Western Australia

“…Determination of consistent differences in DNA sequences is a complementary tool to morphological analysis for assessing taxon distinctness. The most frequently sequenced regions of the plant genome for the investigation of species-level relationships are the internal transcribed spacer (ITS) of nuclear rDNA (see Baldwin et al 1995 for a review; Bena et al 1998aBena et al , 1998b and the trnL-trnF spacer in the chloroplast genome (see Sang et al 1997 for a review; Bayer et al 2000), and an analysis of these regions was undertaken to investigate relationships within the T. aphylla-T. paynterae-T. harperi group of 'leafless' species from the Koolyanobbing area and the taxonomic status of the newly identified, unclassified collections affiliated with these species. A molecular systematic study of these taxa can also be used to investigate the phylogenetic signal of putatively significant morphological characters, such as ovule number and the leafless condition, as well as elucidate the biogeographical relationships between these rare ironstone endemics and their affiliates.…”