Isolation and sequence analysis of the arbuscular mycorrhizal fungus Glomus mosseae (Nicol & Gerd.) Gerdemann & Trappe 3-phosphoglycerate kinase (PGK) gene promoter region.

The Glomus mosseae 3-phosphoglycerate kinase (GmPGK) gene promoter has been isolated from a phage genomic library and represents one of the few promoter elements to be isolated and analysed from these symbiotic fungi. The analysis revealed the presence of several motifs which are found in the promoter region of other fungal PGK genes. In particular, DNA sequences homologous to segments of the S. cerevisiae and Rhizopus niveus upstream activating elements (UAS). The importance of these UAS sequences in regulating carbon source in PGK genes is known and the presence of two carbon source regulated UAS sequences in the GmPGK gene promoter and its role in the biology of AM fungi is discussed briefly.

Biolistic transformation of arbuscular mycorrhizal fungi. Progress and perspectives.

Gene transfer systems have proved effective for the transformation of a range of organisms for both fundamental and applied studies. Biolistic transformation is a powerful method for the gene transfer into various organisms and tissues that have proved recalcitrant to more conventional means. For fungi, the biolistic approach is particularly effective where protoplasts are difficult to obtain and/or the organisms are difficult to culture. This is particularly applicable to arbuscular mycorrhizal (AM) fungi, being as they are obligate symbionts that can only be propagated in association with intact plants or root explants. Furthermore, these fungi are aseptate and protoplasts cannot be released. Recent advancements in gene transformation systems have enabled the use of biolistic technology to introduce foreign DNA linked to molecular markers into these fungi. In this review we discuss the development of transformation strategies for AM fungi by biolistics and highlight the areas of this technology which require further development for the stable transformation of these elusive organisms.

The arbuscular mycorrhizal symbiosis: a molecular review of the fungal dimension.

Mycorrhizal associations vary widely in structure and function, but the most common interaction is the arbuscular mycorrhizal (AM) symbiosis. This interaction is formed between the roots of over 80% of all terrestrial plant species and Zygomycete fungi from the Order Glomales. These fungi are termed AM fungi and are obligate symbionts which form endomycorrhizal symbioses. This symbiosis confers benefits directly to the host plant's growth and development through the acquisition of P and other mineral nutrients from the soil by the fungus. In addition, they may also enhance the plant's resistance to biotic and abiotic stresses. These beneficial effects of the AM symbiosis occur as a result of a complex molecular dialogue between the two symbiotic partners. Identifying the molecules involved in the dialogue is a prerequisite for a greater understanding of the symbiosis. Ongoing research attempts to understand the underlying dialogue and concomitant molecular changes occurring in the plant and the fungus during the establishment of a functioning AM symbiosis. This paper focuses on the molecular approaches being used to study AM fungal genes being expressed in the symbiotic and asymbiotic stages of its lifecycle. In addition, the importance of studying these fungi, in relation to understanding plant processes, is discussed briefly.

Isolation of the 3-phosphoglycerate kinase gene of the arbuscular mycorrhizal fungus Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe.

The 3-phosphoglycerate kinase (PGK) gene of the arbuscular mycorrhizal fungus Glomus mosseae has been isolated by differential RNA display (DD). Experimentally, the technique of DD was utilized to simultaneously compare the mRNA transcript populations from Lycopersicon esculentum root systems colonized by the arbuscular mycorrhizal fungus G. mosseae and non-mycorrhizal plants. A differentially expressed band was isolated and cloned from mycorrhizal tissue. The isolated DD fragment was screened and sequenced. A reverse transcription-PCR (RT-PCR) technique detected transcripts in germinated spores and G. mosseae-colonized root systems but not in uncolonised root systems. The full-length cDNA was isolated by RACE and corresponded to the 3-phosphoglycerate kinase gene of G. mosseae. The cDNA encodes a polypeptide of 416 amino acids, with a predicted molecular weight of 44 764 Da. The PGK proteins shows high homology to those PGKs of other fungi and the phylogenetic relationship among 14 isolated fungal PGK sequences is illustrated.