A homolog of Ste6p, the a-factor transporter in Saccharomyces cerevisiae, functions bilaterally in Cryptococcus neoformans

• Main Authors: Yen-Ping Hsueh, 薛雁冰
• Other Authors: Wei-Chiang Shen
• Format: Others
• Language: en_US
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/83547066193117256767

碩士 === 國立臺灣大學 === 植物病理學研究所 === 91 === Fungal pheromones have been demonstrated to function in the initial recognition of the fungal mating process. One type of peptide pheromones, identified in the Ascomycetes and Basidiomycetes, terminate in a conserved CAAX motif which triggers sequential post-translational modifications of the pheromone precursors. Among this type of peptide pheromones, a well-studied one is the a-factor of Saccharomyces cerevisiae. The mature a-factor is exported from the cell via an alternative mechanism involving the ATP-binding cassette transporter Ste6p, which is distinct from the typical secretory pathway utilized by most peptides. Unlike the Ascomycetes, the basidiomycetous fungi produce only CAAX motif containing lipopeptide pheromones. Cryptococcus neoformans, a human pathogenic basidiomycetous yeast, causes the life-threatening meningoencephalitis mainly in individuals with compromised immune functions. Virulence studies of the congenic pair of C. neoformans strains have shown that MATa cells are more virulent than MATa cells. Characterization of the mating pheromone genes in the MATa strains suggested an autocrine signaling loop may function and contribute to the virulence of the MATa cells. To further address the role of pheromone in the signaling loop, we have identified STE6 homolog in the C. neoformans genome project at SGTC and begun to dissect its function. By disrupting the STE6, we found that ste6 mutants in either MATa or MATa background showed partially impaired mating function. However, when ste6 MATa and MATa mutants cross with each other, the mating process was completely abolished. Surprisingly, MATa ste6 mutant does not exhibit a defect in haploid fruiting, which implicates that the pheromone molecules could induce the signaling response intracellularly in MATa cells. Our data indicates that the STE6 functions bilaterally and is required for mating but not for haploid fruiting in C. neoformans.