Glomales SSUrRNA gene diversity

Abstract

The arbuscular mycorrhiza (AM) is one of the most important symbioses on earth, formed between about 80% of vascular plants and AM fungi (Smith & Read, 1997), which are placed in the order Glomales (Morton & Benny, 1990). A discussion has recently arisen about the rDNA-gene and general genome organization of this fungal group, which, as far as is known, does not possess sexuality (Sanders, 1999). This discussion mainly arose as a result of the assumption that one spore of an AM fungus (Scutellospora castanea) contains small subunit (SSU) rRNA genes that belong, phylogenetically, to different families within the Glomales, namely the Gigasporaceae and Glomaceae (Hosny et al., 1999). Questions about genetic drift, infrequent recombination, concerted evolution and the validity of phylogenetic techniques have arisen (Hosny et al., 1999; Sanders, 1999). However, this assumption might well be based on the sequence of an Ascomycete contaminant.