釀酒酵母菌(Saccharomyces cerevisiae)在一般環境中能以單細胞形態存在也能以多細胞的方式聚集生長，群體聚集生長有助於微生物因應環境變化提升生存適應性，目前有許多研究著手於酵母菌多細胞聚集生長所帶來的效益，例如多細胞生長的凝絮現象(flocculation)能使酵母菌藉由外部細胞屏障保護內部細胞免於環境壓力影響，提升族群生存適應性。然而酵母菌的多細胞生長型態除了凝絮現象外，還有交配聚合現象(mating aggregation)及鏈形聚集現象(chain-formation)，而目前研究對於鏈型聚集現象對酵母菌群體的影響尚無深入了解，本研究就是欲探討釀酒酵母菌的鏈形聚集現象對釀酒酵母菌本身生存競爭的影響。生物表型差異可來自基因調控機制的不同所造成，本研究發現釀酒酵母菌野生菌株RM系列的RM11-1A為單倍體且具有鏈形聚集現象(chain-formation)而同基因型雙倍體菌株RM11則不具有多細胞聚集表型，經比對單倍體與雙倍體酵母菌基因表現資料我發現大約有一百多個基因在單倍體與雙倍體酵母菌之間是有差異的，其中與細胞分裂進而造成細胞聚集的基因AMN1(Antagonist of Mitotic exit Network)基因在單倍體中的表現量是雙倍體中的兩倍，因此我認為AMN1基因在單倍體與雙倍體酵母菌中表現量的差異可能是導致單倍體酵母菌帶有多細胞聚集表型而同基因型雙倍體菌株RM11則不具有多細胞聚集表型的原因之一，所以我透過基因轉殖技術提高AMN1基因在雙倍體RM11酵母菌細胞的表現量，以檢視AMN1基因的表現量與雙倍體RM11酵母菌聚集表型之關聯。在此研究中我發現AMN1基因表現量的高低會影響RM11雙倍體釀酒酵母菌的聚集表型與生存適應能力，且AMN1基因表現量變異導致RM11雙倍體酵母菌聚集表型的細胞的生存能力顯著較弱。在野生株(RM)與實驗室株(BY)共培養10天的生存能力比較中發現單倍體野生株生存能力明顯優於單倍體實驗室株，而雙倍體間生存能力無顯著差異。且發現AMN1基因過表現之雙倍體野生株酵母菌生存能力顯著弱於AMN1基因無意突變的雙倍體實驗室株酵母菌。因此本篇確定在酵母菌中影響細胞週期退出有絲分裂網路的AMN1基因表現量所造成的鏈型聚集現象生長與菌株生存能力相關。

The budding yeast Saccharomyces cerevisiae could exist as a single cell organism or exist as in multicellular form such as flocculation, aggregation or biofilm in nature. It is believed that the flocculation of cells could help yeast to cope with the changes of environment because the outer layer of cells might protect the inner layer of cells from the harsh environment. However, this theory has not been tested in the multicellular cell type resulted from incomplete cell division (chain-formation multicellular cell type). It is known that the AMN1 gene is the key regulator for chain-formation cell aggregation phenotype. Yeast cells will not aggregate if the 368th amino acid of the AMN1p protein is valine instead of aspartic acid. In addition, my lab also observed that the diploid yeast strain RM11 which carry the wild type AMN1 gene does not show the same aggregation phenotype as the same genetic background haploid strain, RM11-1a. It is reasonable to assume that the different aggregation phenotype between diploid RM11 strain and haploid RM11-1a strain could be the results of differential gene expression of AMN1 gene between diploid strain and haploid strain. In this study, I constructed an overexpression AMN1 diploid yeast strain to examine if the lower AMN1 expression of the diploid yeast was responsible for the non-aggregation phenotype of diploid yeast. Furthermore, I examined if the overexpression of AMN1 gene affect the fitness of diploid yeast.

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