Departamento de Ingeniería Genética, Unidad Irapuato, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Gto., México.
Licenciatura en Microbiología, Universidad Autónoma de Querétaro, Querétaro, México.
Microbiology (Reading). 2012 Mar;158(Pt 3):674-684. doi: 10.1099/mic.0.055954-0. Epub 2012 Jan 5.
Synthesis of spermidine involves the action of two enzymes, spermidine synthase (Spe) and S-adenosylmethionine decarboxylase (Samdc). Previously we cloned and disrupted the gene encoding Spe as a first approach to unravel the biological function of spermidine in Ustilago maydis. With this background, the present study was designed to provide a better understanding of the role played by Samdc in the regulation of the synthesis of this polyamine. With this aim we proceeded to isolate and delete the gene encoding Samdc from U. maydis, and made a comparative analysis of the phenotypes of samdc and spe mutants. Both spe and samdc mutants behaved as spermidine auxotrophs, and were more sensitive than the wild-type strain to different stress conditions. However, the two mutants displayed significant differences: in contrast to spe mutants, samdc mutants were more sensitive to LiCl stress, high spermidine concentrations counteracted their dimorphic deficiency, and they were completely avirulent. It is suggested that these differences are possibly related to differences in exogenous spermidine uptake or the differential location of the respective enzymes in the cell. Alternatively, since samdc mutants accumulate higher levels of S-adenosylmethionine (SAM), whereas spe mutants accumulate decarboxylated SAM, the known opposite roles of these metabolites in the processes of methylation and differentiation offer an additional attractive hypothesis to explain the phenotypic differences of the two mutants, and provide insights into the additional roles of polyamine metabolism in the physiology of the cell.
精胺的合成涉及两种酶的作用，精胺合酶（Spe）和 S-腺苷甲硫氨酸脱羧酶（Samdc）。之前，我们克隆并破坏了编码 Spe 的基因，作为揭示精胺在构巢曲霉中的生物学功能的第一步。在此背景下，本研究旨在更好地了解 Samdc 在这种多胺合成中的调节作用。为此，我们从构巢曲霉中分离并删除了编码 Samdc 的基因，并对 samdc 和 spe 突变体的表型进行了比较分析。spe 和 samdc 突变体均表现为精胺营养缺陷型，并且比野生型菌株对不同的应激条件更敏感。然而，这两个突变体表现出显著的差异：与 spe 突变体不同，samdc 突变体对 LiCl 应激更敏感，高浓度的精胺可抵消其二态缺陷，且它们完全丧失毒力。这表明这些差异可能与细胞中外源精胺摄取的差异或相应酶在细胞中的不同位置有关。或者，由于 samdc 突变体积累了更高水平的 S-腺苷甲硫氨酸（SAM），而 spe 突变体积累了脱羧的 SAM，这些代谢物在甲基化和分化过程中的相反作用提供了一个额外的诱人假说，以解释这两个突变体的表型差异，并为多胺代谢在细胞生理学中的额外作用提供了新的见解。
