Abstract
Microbial cells interact with the environment by adapting to external changes. Signal transduction pathways participate in both sensing and responding in the form of modification of gene expression patterns, enabling cell survival. The filamentous fungal-specific SltA pathway regulates tolerance to alkalinity, elevated cation concentrations and, as shown in this work, also stress conditions induced by borates. Growth of sltA− mutants is inhibited by increasing millimolar concentrations of boric acid or borax (sodium tetraborate). In an attempt to identify genes required for boron-stress response, we determined the boric acid or borax-dependent expression of sbtA and sbtB, orthologs of Saccharomyces cerevisiae bor1, and a reduction in their transcript levels in a ΔsltA mutant. Deletion of sbtA, but mainly that of sbtB, decreased the tolerance to boric acid or borax. In contrast, null mutants of genes coding for additional transporters of the Solute Carrier (SLC) family, sB, sbtD or sbtE, showed an unaltered growth pattern under the same stress conditions. Taken together, our results suggest that the SltA pathway induces, through SbtA and SbtB, the export of toxic concentrations of borates, which have largely recognized antimicrobial properties.
Highlights
The interaction of organisms with the environment involves sensing and responding mechanisms.Filamentous fungi have developed multiple signal–transduction pathways
Some of them induce developmental responses under suboptimal growth conditions or in the presence of abiotic signals such as those involving air or light [1,2,3]. Others, such as those controlled by transcription factors (TFs) AP-1, PacC/Rim101, Crz1 or SltA/Ace1, act as principal regulatory mechanisms to minimize the effect of oxygen or nitrogen species (AP-1), control pH homeostasis (PacC/Rim101), and avoid a toxic intracellular accumulation of numerous mono and divalent cations (Crz1 and SltA/Ace1) [4,5,6,7]
We identified by BLAST searches two putative orthologs of Bor1 in A. nidulans, AN4904 and AN0218
Summary
The interaction of organisms with the environment involves sensing and responding mechanisms.Filamentous fungi have developed multiple signal–transduction pathways. Some of them induce developmental responses under suboptimal growth conditions or in the presence of abiotic signals such as those involving air or light [1,2,3]. Others, such as those controlled by transcription factors (TFs) AP-1, PacC/Rim101, Crz or SltA/Ace, act as principal regulatory mechanisms to minimize the effect of oxygen or nitrogen species (AP-1), control pH homeostasis (PacC/Rim101), and avoid a toxic intracellular accumulation of numerous mono and divalent cations (Crz and SltA/Ace1) [4,5,6,7].
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