Abstract
BackgroundPhytochelatin synthase (PCS) is an enzyme that catalyzes the biosynthesis of phytochelatin from glutathione. Phytochelatins protect cells against the toxic effects of non-essential heavy metals, such as cadmium, and hence growth is restricted in the presence of these metals in mutants in PCS-encoding genes. PCS genes from fungi have been characterized in only two species in the Ascomycota, and these genes are considered sparsely distributed in the fungal kingdom.ResultsA gene encoding a putative PCS was identified in Sporobolomyces sp. strain IAM 13481, a fungus that is a member of the Pucciniomycotina subphylum of the Basidiomycota. The function of this PCS1 gene was assessed by heterologous expression in the Ascomycota yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe, and by mutating the gene in Sporobolomyces. The gene is required for tolerance to toxic concentrations of non-essential cadmium as well as the essential metal copper. Pcs1 homologs in fungi and other eukaryotes have putative targeting sequences for mitochondrial localization: the S. pombe homolog was fused to green fluorescent protein and it co-localized with a mitochondrial dye. Evaluation of the presence or absence of PCS and PCS-like homologs in the genome sequences of fungi indicates that they have a wide distribution, and the absence in most Ascomycota and Basidiomycota (the Dikarya) species can be explained by a small number of gene losses.ConclusionsThe ecology of the species within the fungi carrying putative PCS genes, the phenotypes of phytochelatin synthase mutants in two major fungal lineages, and the presence of homologs in many non-Dikarya lineages parallel what is seen in the plant and animal kingdoms. That is, PCS is a protein present early during the evolution of the fungi and whose role is not solely dedicated to combating toxic concentrations of non-essential metals.Electronic supplementary materialThe online version of this article (doi:10.1186/s40694-015-0013-3) contains supplementary material, which is available to authorized users.
Highlights
Phytochelatin synthase (PCS) is an enzyme that catalyzes the biosynthesis of phytochelatin from glutathione
Sporobolomyces sp. encodes a putative phytochelatin synthase homolog that can protect S. cerevisiae from toxic levels of heavy metals A putative phytochelatin synthase (PCS) homolog was identified during the analysis and annotation of the genome sequence of a strain of Sporobolomyces
One approach used to clone phytochelatin synthases from plants was to express plant cDNAs in a S. cerevisiae strain with a yap1 mutation and identify cadmiumresistant transformants
Summary
Phytochelatin synthase (PCS) is an enzyme that catalyzes the biosynthesis of phytochelatin from glutathione. Phytochelatins protect cells against the toxic effects of non-essential heavy metals, such as cadmium, and growth is restricted in the presence of these metals in mutants in PCS-encoding genes. Metal ions are cofactors that are required for many enzymes and transcriptional regulators, yet these same essential metals can become toxic at high concentrations, and non-essential metals are often toxic [1]. Organisms have different mechanisms to tolerate or combat exposure to high levels of metals. Understanding those mechanisms and employing this information has many. One approach used by organisms to avoid metal toxicity is to chelate metal ions with another molecule to sequester the metal within the cell. A gene encoding a phytochelatin synthase was identified in the late 1990s in three independent studies.
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