Diversity of the ribosomal internal transcribed spacers within and among isolates of Glomus mosseae and related mycorrhizal fungi

Abstract

SUMM.4RYThe internal transcribed spacer (ITS) region of the nuclear ribosomal RNA was amplified, cloned and sequenced from spores of five isolates of the arbuscular mycorrhizal fungus Glomus mosseae and one isolate each of G. fasciculatum, G. dimorphicum and G. coronatiim. The sequences comprised ITSl (113-121 base pairs), 5.SS rRNA gene (154 base pairs) and ITS2 (222-230 base pairs). The ITS sequences were at least 84% identical, but only distantly related to other published sequences. Their identification as Glomus sequences was confirmed by sequencing part of the adjoining SSU rRNA gene from one isolate; it was 98 °o identical to the published G. mosseae sequence. Two to four clones were sequenced from each isolate, and in many instances these were substantially different (up to 6 % divergence) even when they were obtained from a single spore. Sequences from a single isolate were generally, but not always, more similar to each other than to those from different isolates. In addition to base substitutions, many ITS sequences differed slightly in length because of the insertion or deletion of up to three nucleotides within short runs of a single base, generally A or T. These changes were found at 22 separate sites within the ITS, and were more common between than within isolates. Phylogenetic relationships deduced from length variation and from base substitution were similar. The variation among isolates from different continents (Europe, Asia, South America) was no greater than among those from a smaller geographic range. The ITSl and 2 sequences from G. coronatum were clearly distinct from the other isolates (11-16% divergence), but those of G. fasciculatum and G. dimorphicum fell w-ithin the range of variation exhibited by G. mosseae.

Phylogeny of the Glomales: deciphering the past to understand the present

“…Although it is not clear how frequently such an ITS polymorphism occurs in glomalean fungi, this phenomenon should be taken into account w-hen comparing ITS sequences from different isolates. It may prove difficult to distinguish the sequence divergence observed between species or isolates from the background of intraspore or intraisolate polymorphism (Lloyd-MacGilp et al, 1996).…”

PCR-Denaturing Gradient Gel Electrophoresis Profiling of Inter- and Intraspecies 18S rRNA Gene Sequence Heterogeneity Is an Accurate and Sensitive Method To Assess Species Diversity of Arbuscular Mycorrhizal Fungi of the GenusGigaspora

“…Molecular analyses have revealed that a single AMF isolate or even individual spores may contain substantial heterogeneity among rRNA gene copies (2,12,31,33,34,40; for a recent review, see reference 41), which may be unevenly distributed in the heterokaryotic nuclei of AMF spores (31,54). Intraspecific rRNA heterogeneity seems to be a common phenomenon in AMF as well as in other groups of organisms, such as bacteria (1,37), plants (11), insects (52), and crustaceans (18).…”

Genetic Diversity of Isolates of Glomus mosseae from Different Geographic Areas Detected by Vegetative Compatibility Testing and Biochemical and Molecular Analysis

“…The high frequency of anastomosis formation and the establishment of protoplasmic continuity between fused hyphae suggested that the ability of self-compatible hyphae to recognize each other could represent a means for the exchange of genetic material, particularly if anastomoses occurred between hyphae derived from genetically different spores (15,26). Several studies have reported that individual spores of AM fungi, which are multinucleate (they may contain thousands of nuclei [7,53]) show a high level of genetic diversity in the internal transcribed spacer (ITS) region of the nuclear rRNA genes (3,28,30,42). Since AM fungi are considered clonal organisms (40), anastomoses between different germlings may represent a mechanism for the maintenance of genetic diversity in the absence of sexual recombination (6,41).…”