Regulation of Salt Tolerance by Torulaspora delbrueckii Calcineurin Target Crz1p

摘要

Recently, the academic interest in the yeast Torulaspora delbrueckii has increased notably due to its high resistance to several types of stress, including salt and osmotic imbalance. However, the molecular mechanisms underlying these unusual properties are poorly understood. In Saccharomyces cerevisiae, the high-salt response is mediated by calcineurin, a conserved Ca2+/calmodulin-modulated protein phosphatase that regulates the transcriptional factor Crz1p. Here, we cloned the T. delbrueckii TdCRZ1 gene, which encodes a putative zinc finger transcription factor homologue to Crz1p. Consistent with this, overexpression of TdCRZ1 enhanced the salt tolerance of S. cerevisiae wild-type cells and suppressed the sensitivity phenotype of cnb1Δ and crz1Δ mutants to monovalent and divalent cations. However, T. delbrueckii cells lacking TdCrz1p showed phenotypes distinct from those previously observed in S. cerevisiae crz1Δ mutants. Quite remarkably, Tdcrz1-null cells were insensitive to high Na+ and were more Li+ tolerant than wild-type cells. Clearly, TdCrz1p was not required for the salt-induced transcriptional activation of the TdENA1 gene, encoding a putative P-type ATPase homologue to the main S. cerevisiae Na+ pump ENA1. Furthermore, T. delbrueckii cells were insensitive to the immunosuppressive agents FK506 and cyclosporine A, both in the presence and in the absence of NaCl. Signaling through the calcineurin/Crz1 pathway appeared to be essential only on high-Ca2+/Mn2+ media. Hence, T. delbrueckii and S. cerevisiae differ in the regulatory circuits and mechanisms that drive the adaptive response to salt stress.