Dissection of the molecular mechanisms regulating the blue light photoresponses in Cryptococcus neoformans
Date Issued
2005
Date
2005
Author(s)
Sun, Kai-Hui
DOI
en-US
Abstract
Light affects growth and development of various organisms, including fungi. Cryptococcus neoformans, an opportunistic human fungal pathogen, is a heterothallic basidiomyceteous fungus that grows vegetatively as a yeast under normal conditions. Under nitrogen limitation conditions, cells of opposite mating type, MATa and MATα, fuse to form dikaryotic filaments, and subsequently produce the meiotic basidiospores. Our prior studies have shown that C. neoformans can only sense blue light and its sexual filamentation is negatively regulated by light. To dissect the molecular mechanisms of light signaling in C. neoformans, the CWC1 gene, a homologue of the Neurospora crassa wc-1, has been identified and characterized. Inhibition of sexual filamentation by CWC1 overexpression requires light activation suggested that the putative LOV domain-containing Cwc1 protein may function as the blue light photoreceptor in C. neoformans. In this study, through a candidate gene approach, we report the identification and characterization of C. neoformans CWC2 gene, a homologue of the N. crassa wc-2. Analysis of Cwc2 amino acid sequence revealed that the putative PAS domain and GATA-type zinc finger DNA-binding domain are present. Deletion of the CWC2 gene similarly results in loss of light inhibition of the sexual filamentation as the cwc1 mutants, suggesting that CWC2 is also crucial in the blue light response pathway in C. neoformans. In addition, gene expression analysis showed that the CWC2 gene is slightly up-regulated in response to light, and light dependent activation of the Cwc2 protein is also required for its proper function. Based on the results, we propose two models in which Cwc1 functions as a blue light photoreceptor to mediate photoresponses through complexing with the conserved DNA-binding domain containing Cwc2 via the conserved protein dimerization PAS domains. Furthermore, a putative repressor Tup1 homologue potentially downstream of the Cwc complex was identified. To determine the role of C. neoformans TUP1 gene, we conducted epistasis analysis and created the cwc mutant strains under tup1 mutant background. Preliminary results suggested that Tup1 may function downstream of the Cwc complex; however, additional repressor(s) may be present and coordinately regulate C. neoformans genes involved in the sexual filamentation. To identify genes under direct control of Cwc complex and also involved in light-regulated filamentation or other biological processes in C. neoformans, subtractive screen approaches were also employed. Although no putative repressor has been identified so far, some genes of interest have been isolated. Further characterization is required to reveal their functions.
Subjects
隱球菌
藍光
訊息傳導
Cryptococcus neoformans
blue light
CWC
TUP1
Type
other
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