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FluG-dependent asexual development in Aspergillus nidulans occurs via derepression.

ABSTRACT: The asexual spore is one of the most crucial factors contributing to the fecundity and fitness of filamentous fungi. Although the developmental activator FluG was shown to be necessary for activation of asexual sporulation (conidiation) and production of the carcinogenic mycotoxin sterigmatocystin (ST) in the model filamentous fungus Aspergillus nidulans, the molecular mechanisms underlying the developmental switch have remained elusive. In this study, we report that the FluG-mediated conidiation in A. nidulans occurs via derepression. Suppressor analyses of fluG led to the identification of the sfgA gene encoding a novel protein with the Gal4-type Zn(II)2Cys6 binuclear cluster DNA-binding motif at the N terminus. Deletion (delta) and 31 other loss-of-function sfgA mutations bypassed the need for fluG in conidiation and production of ST. Moreover, both delta sfgA and delta sfgA delta fluG mutations resulted in identical phenotypes in growth, conidiation, and ST production, indicating that the primary role of FluG is to remove repressive effects imposed by SfgA. In accordance with the proposed regulatory role of SfgA, overexpression of sfgA inhibited conidiation and delayed/reduced expression of conidiation- and ST-specific genes. Genetic analyses demonstrated that SfgA functions downstream of FluG but upstream of transcriptional activators (FlbD, FlbC, FlbB, and BrlA) necessary for normal conidiation.

SUBMITTER: Seo JA

PROVIDER: S-EPMC1456305 | biostudies-literature | 2006 Mar

REPOSITORIES: biostudies-literature

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FluG-dependent asexual development in Aspergillus nidulans occurs via derepression.

Seo Jeong-Ah JA Guan Yajun Y Yu Jae-Hyuk JH

Genetics 20051230 3

The asexual spore is one of the most crucial factors contributing to the fecundity and fitness of filamentous fungi. Although the developmental activator FluG was shown to be necessary for activation of asexual sporulation (conidiation) and production of the carcinogenic mycotoxin sterigmatocystin (ST) in the model filamentous fungus Aspergillus nidulans, the molecular mechanisms underlying the developmental switch have remained elusive. In this study, we report that the FluG-mediated conidiatio ...[more]

PMID: 16387865

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Project description:The central developmental pathway (CDP) activator gene brlA is activated by the upstream genes fluG and flbA-flbE in Aspergillus nidulans. Increasing evidences of fungal genome divergence make it necessary to clarify whether such genetic principles fit Pezizomycotina. Previously, fluG disruption resulted in limited conidiation defect and little effect on the expression of brlA and flbA-flbE in Beauveria bassiana possessing the other FluG-like regulator FlrA. Here, single-disruption (SD) mutants of flrA and double-disruption (DD) mutants of flrA and fluG were analyzed to clarify whether FlrA and FluG are upstream regulators of key CDP genes. Despite similar subcellular localization, no protein-protein interaction was detected between FlrA and FluG, suggesting mutual independence. Three flrA SD mutants showed phenotypes similar to those previously described for ΔfluG, including limited conidiation defect, facilitated blastospore production, impaired spore quality, blocked host infection, delayed proliferation in vivo, attenuated virulence, and increased sensitivities to multiple stresses. Three DD mutants resembled the SD mutants in all phenotypes except more compromised pathogenicity and tolerance to heat shock- or calcofluor white-induced stress. No CDP gene appeared in 1,622 and 2,234 genes dysregulated in the ΔflrA and ΔfluG mutants, respectively. The majority (up/down ratio: 540:875) of those dysregulated genes were co-upregulated or co-downregulated at similar levels in the two mutants. These findings unravel novel roles for flrA and fluG in coregulating manifold gene sets vital for fungal adaptation to insect-pathogenic lifestyle and environment but not involved in CDP activation. IMPORTANCE FluG is a core regulator upstream of central developmental pathway (CDP) in Aspergillus nidulans but multiple FluG-like regulators (FLRs) remain functionally uncharacterized in ascomycetes. Our previous study revealed no role for FluG in the CDP activation and an existence of sole FLR (FlrA) in an insect-pathogenic fungus. This study reveals a similarity of FlrA to FluG in domain architecture and subcellular localization. Experimental data from analyses of targeted single- and double-gene knockout mutants demonstrate similar roles of FrlA and FluG in stress tolerance and infection cycle but no role of either in CDP activation. Transcriptomic analyses reveal that FlrA and FluG coregulate a large number of same genes at similar levels. However, the regulated genes include no key CDP gene. These findings uncover that FlrA and FluG play similar roles in the fungal adaptation to insect-pathogenic lifestyle and environment but no role in the activation of CDP.

Dataset Information

FluG-dependent asexual development in Aspergillus nidulans occurs via derepression.

Publications

FluG-dependent asexual development in Aspergillus nidulans occurs via derepression.

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