, Volume 212, Issue 1-2, pp 89-98

A homologue of the cell cycle check point TOR2 fromSaccharomyces cerevisiae exists in the arbuscular mycorrrhizal fungusGlomus mosseae

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A homologue of the geneTOR2 fromSaccharomyces cere isiae has been found in the arbuscular mycorrhizal (AM) fungusGlomus mosseae (BEG 12) during a differential RNA display experiment. Further downstream sequence was obtained by a nested-PCR approach. Eight introns were found in 2.6 kb sequence. The fragment encodes a putative protein with high homology (53% identity) to the C terminus ofS. cere isiae TOR2 and its homologues inSchizosaccharomyces pombe and humans. The gene was namedGmTOR2. The expression of the gene was studied by reverse transcriptase-polymerase chain reaction and it was found to be expressed at a relatively high level during all the different life cycle stages of the AM fungus. TOR2 is known to be involved in the control of the cell cycle inS. cere isiae and the organization of the actin cytoskeleton in response to nutrients. The anti-inflammatory drug rapamycin, known to interfere with the role of TOR2 controlling the arrest of the cell cycle in G1 but not with its signalling to the actin cytoskeleton, was found to decrease hyphal growth ofG. mosseae sporocarps but not to affect spore germination. This result confirms that DNA replication is not needed for germination but during the presymbiotic growth. The immunostaining of germinated sporocarps ofG. mosseae with antibodies against tubulin showed the presence of mitotic spindles in some secondary spores, confirming previous findings of DNA replication during presymbiosis. The possibility that GmTOR2 controls the cell cycle arrest in AM fungi in the absence of the plant as a response to nutrient starvation is discussed.