Regulation of Salt Tolerance byTorulaspora delbrueckiiCalcineurin Target Crz1p

Abstract

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 Ca 2؉ /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 cnb1⌬ and crz1⌬ mutants to monovalent and divalent cations. However, T. delbrueckii cells lacking TdCrz1p showed phenotypes distinct from those previously observed in S. cerevisiae crz1⌬ 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-Ca 2؉ /Mn 2؉ media. Hence, T. delbrueckii and S. cerevisiae differ in the regulatory circuits and mechanisms that drive the adaptive response to salt stress.

Calcineurin-Crz1 Signaling in Lower Eukaryotes

“…In the social amoeba D. discoideum, Na ϩ sensitivity could be observed for the TacA-RNAi (TacA-RNA interference) mutant (19). Interestingly, for T. delbrueckii and D. discoideum, perturbation of Crz1 signaling leads to increased resistance to Li ϩ (19,21). Together with the misregulation of genes involved in ion homeostasis (Table 1), these observations show that Crz1 is involved in resistance and sensitivity to different metal ions in a species-specific manner.…”

“…Besides defects in cell cycle control, ⌬crz1 mutants have defects mainly under conditions of Ca 2ϩ -and Na ϩ stress in S. cerevisiae. Additional defects with respect to other cations such as Mn 2ϩ , K ϩ , and Li ϩ have also been observed to various extents in other yeasts such as Torulaspora delbrueckii (21), S. pombe (15), C. albicans (20,22,29), Candida dubliniensis (65), and Candida lusitaniae (66) and in filamentous fungi such as A. nidulans (17,24), A. fumigatus (16), Aspergillus parasiticus (25), Penicillium digitatum (67), Magnaporthe grisea (26), and M. oryzae (27). In the social amoeba D. discoideum, Na ϩ sensitivity could be observed for the TacA-RNAi (TacA-RNA interference) mutant (19).…”

Calcineurin-Responsive Zinc Finger Transcription Factor CRZ1 of Botrytis cinerea Is Required for Growth, Development, and Full Virulence on Bean Plants

“…In addition, the expression of GPX2 was inducible by Ca 2ϩ in a calcineurin-and CRZ1-dependent manner (72,73). SKN7 has been shown to be a multicopy enhancer of calcineurin-and CRZ1-dependent transcription in yeast, proposing a model in which SKN7 regulates calcineurin signaling through the stabilization of CRZ1 via a direct protein-protein interaction (82 (28). All these data show that the calcineurin/CRZ1 signaling pathway has some conserved functions, such as the regulation of cell wall/membrane integrity and the general stress response and some fungus-specific functions, reflecting the evolution of calcineurin/CRZ1 signaling output due to the adaptation of the organisms to their environmental niches.…”

The Aspergillus fumigatus P-Type Golgi Apparatus Ca 2+ /Mn 2+ ATPase PmrA Is Involved in Cation Homeostasis and Cell Wall Integrity but Is Not Essential for Pathogenesis

“…Calcineurin, a conserved serine/threonine-specific phosphatase, mediates environmental stress adaptation in fungi through the transcription factor Crz1/Prz1/CrzA (4,6,9,10,12,16,22). The P-type ATPases, encoded by PMR1, PMC1, and ENA1, have also been characterized as targets of calcineurin in Saccharomyces cerevisiae (3,5,11,20), but their filamentous fungal counterparts have not been completely investigated.…”