Abstract
Glutathione S-transferases (GSTs) compose a family of multifunctional enzymes that play important roles in the detoxification of xenobiotics and the oxidative stress response. In the present study, twenty four GST genes from the transcriptome of a metal-tolerant dark septate endophyte (DSE), Exophiala pisciphila, were identified based on sequence homology, and their responses to various heavy metal exposures were also analyzed. Phylogenetic analysis showed that the 24 GST genes from E. pisciphila (EpGSTs) were divided into eight distinct classes, including seven cytosolic classes and one mitochondrial metaxin 1-like class. Moreover, the variable expression patterns of these EpGSTs were observed under different heavy metal stresses at their effective concentrations for inhibiting growth by 50% (EC50). Lead (Pb) exposure caused the up-regulation of all EpGSTs, while cadmium (Cd), copper (Cu) and zinc (Zn) treatments led to the significant up-regulation of most of the EpGSTs (p < 0.05 to p < 0.001). Furthermore, although heavy metal-specific differences in performance were observed under various heavy metals in Escherichia coli BL21 (DE3) transformed with EpGSTN-31, the over-expression of this gene was able to enhance the heavy metal tolerance of the host cells. These results indicate that E. Pisciphila harbored a diverse of GST genes and the up-regulated EpGSTs are closely related to the heavy metal tolerance of E. pisciphila. The study represents the first investigation of the GST family in E. pisciphila and provides a primary interpretation of heavy metal detoxification for E. pisciphila.
Highlights
Endophytic fungi that cause asymptomatic infections in living plant tissues have been widely studied in various environments [1]
A total of 24 non-redundant gene loci were predicted to code for putative full-length Glutathione S-transferases (GSTs) proteins in E. pisciphila
The proteins included in the Ure2p-like, N-2 (GST_N family, unknown subfamily 2), N-3 (GST_N family, unknown subfamily 3), zeta, theta, GTT1, EF1Bγ, and metaxin 1-like classes were designated as EpUre2p, EpGSTN-2, EpGSTN-3, EpGSTZ, EpGSTT, EpGSTG, EpEF1Bγ and EpMetaxin1, respectively (Fig 1)
Summary
Endophytic fungi that cause asymptomatic infections in living plant tissues have been widely studied in various environments [1]. Among the highly diverse group of endophytic fungi, dark septate endophytes (DSE) are characterized by their darkly pigmented and septate hyphae. These melanocratic fungi have been found to ubiquitously colonize the roots of plants growing in extremely heavy metal-contaminated soil [2, 3], and some of them exhibit increased colonization with the increasing levels of heavy metal pollution [4, 5]. One strain of DSE (Exophiala pisciphila), which was isolated from an abandoned lead-zinc mine has shown a relatively high tolerance to heavy metals [2]. The mechanisms of heavy metal tolerance of DSE are far from elaborated
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