Light-dependent regulation of the gene cut-1 of Neurospora, involved in the osmotic stress response

The gene cut-1 from Neurospora encodes a protein of the haloacid dehalogenase (HAD) family, a group of enzymes usually associated to phosphatase or phosphotransferase activities. Loss of cut-1 function results in an osmosensitive phenotype and its transcription is induced by high osmotic pressure or heat-shock, but not by other stressing conditions tested. Unexpectedly, cut-1 transcript levels markedly decrease following illumination in the wild type and in some mutants tested, such as bd and vvd. The reduction was less pronounced in wc-1 and wc-2 mutants, indicating that this photoresponse is principally mediated by the WC system, a conclusion further supported by the lack of effect of blue light in a wc-1 mutant. Additionally, cut-1 mRNA levels are much higher in the dark in wc, vvd, bd, and cut mutants, showing the involvement of these genes in a cut-1 down-regulation mechanism. In the cases investigated, the mRNA levels of these strains increased further under high osmotic conditions, indicating an independent derepression effect. The environmental or genetic factors influencing cut-1 expression have no significant effect on the mRNA levels of two additional Neurospora genes encoding HAD proteins.