Unitat de Microbiologia, Facultat de Medicina i Ciències de la Salut and Institut d'Investigació Sanitària Pere Virgili (IISPV), Universitat Rovira i Virgili, Reus, Spain.
Departamento de Genetica, Facultad de Ciencias and Campus de Excelencia Internacional Agroalimentario ceiA3, Universidad de Cordoba, 14071 Cordoba, Spain.
Metallomics. 2019 Jul 17;11(7):1230-1240. doi: 10.1039/c9mt00081j.
Soil organisms exhibit high tolerance to heavy metals, probably acquired through evolutionary adaptation to contaminated environments. Essentially, metal tolerance in fungi involves several specific and non-specific mechanisms that include metal efflux, metal binding to cell walls, extracellular and intracellular sequestration and complexation with proteins. However, fungi have adopted different strategies to detoxify heavy metals, although species differ in the mechanisms used. In this complex molecular framework, metallothioneins (MTs) are becoming increasingly relevant in metal homeostasis, even though little is known about their role in metal adaptation and virulence in fungal pathogens. With the aim to decipher the function of metallothioneins in the opportunistic fungus Fusarium oxysporum, we have carried out an in silico analysis that revealed the presence of a hypothetical metallothionein (mt1) that has multiple metal responsive elements in its promoter region and conserved cysteine motifs in its coding sequence. Characterization of strain Δmt1 deficient in the mt1 gene revealed higher sensitivity of this mutant to copper, cadmium and zinc compared to the wild type strain (wt). Expression analyses revealed that Zn specifically activates mt1, but the lack of this gene did not lead to a transcriptional up-regulation of genes gapdh and prx, associated with the oxidative stress response. The lack of mt1 did not alter the pathogenic capacity of the fungus, either in tomato plant or in a murine model of systemic infection. Nevertheless, Δmt1 displayed lower resistance to macrophage killing, suggesting a connection between the absence of mt1 and impaired defence capacity against copper and reactive oxygen species.
土壤生物对重金属表现出很高的耐受性，这可能是通过进化适应污染环境而获得的。从本质上讲，真菌的金属耐受性涉及几种特定和非特定的机制，包括金属外排、细胞壁结合金属、细胞外和细胞内隔离以及与蛋白质的络合。然而，真菌已经采用了不同的策略来解毒重金属，尽管不同物种使用的机制不同。在这个复杂的分子框架中，金属硫蛋白（MTs）在金属稳态中变得越来越重要，尽管它们在真菌病原体的金属适应和毒力中的作用知之甚少。为了解释机会性真菌尖孢镰刀菌中金属硫蛋白的功能，我们进行了一项计算机分析，揭示了假定金属硫蛋白（mt1）的存在，其启动子区域有多个金属响应元件，编码序列中有保守的半胱氨酸基序。mt1 基因缺失株 Δmt1 的特性研究表明，与野生型菌株（wt）相比，该突变体对铜、镉和锌的敏感性更高。表达分析表明，Zn 特异性激活 mt1，但缺乏该基因不会导致与氧化应激反应相关的 gapdh 和 prx 基因的转录上调。mt1 的缺失并没有改变真菌的致病能力，无论是在番茄植株还是在系统性感染的小鼠模型中。然而，Δmt1 对巨噬细胞杀伤的抵抗力较低，这表明 mt1 的缺失与铜和活性氧防御能力受损之间存在联系。
