Abstract
Conidiation and sexual development are critical for reproduction, dispersal and better-adapted survival in many filamentous fungi. The Neurospora crassa gene ada-6 encodes a Zn(II)2Cys6-type transcription factor, whose deletion resulted in reduced conidial production and female sterility. In this study, we confirmed the positive contribution of ada-6 to conidiation and sexual development by detailed phenotypic characterization of its deletion mutant and the complemented mutant. To understand the regulatory mechanisms of ADA-6 in conidiation and sexual development, transcriptomic profiles generated by RNA-seq from the Δada-6 mutant and wild type during conidiation and sexual development were compared. During conidial development, differential expressed genes (DEGs) between the Δada-6 mutant and wild type are mainly involved in oxidation-reduction process and single-organism metabolic process. Several conidiation related genes are positively regulated by ADA-6, including genes that positively regulate conidiation (fluffy and acon-3), and genes preferentially expressed during conidial development (eas, con-6, con-8, con-10, con-13, pcp-1, and NCU9357), as the expression of these genes were lower in the Δada-6 mutant compared to wild type during conidial development. Phenotypic observation of deletion mutants for other genes with unknown function down-regulated by ada-6 deletion revealed that deletion mutants for four genes (NCU00929, NCU05260, NCU00116, and NCU04813) produced less conidia than wild type. Deletion of ada-6 resulted in female sterility, which might be due to that ADA-6 affects oxidation-reduction process and transmembrane transport process, and positively regulates the transcription of pre-2, poi-2, and NCU05832, three key genes participating in sexual development. In both conidiation and the sexual development process, ADA-6 regulates the transcription of cat-3 and other genes participating in reactive oxygen species production according to RNA-seq data, indicating a role of ADA-6 in oxidative stress response. This was further confirmed by the results that deletion of ada-6 led to hypersensitivity to oxidants H2O2 and menadione. Together, these results proved that ADA-6, as a global regulator, plays a crucial role in conidiation, sexual development, and oxidative stress response of N. crassa.
Highlights
Conidial production is critical for reproduction, dispersal and survival in many filamentous fungi
Several transcription factors encoding genes named as all development altered were previously identified, and their deletion resulted in significant defects in basal hyphal growth, asexual sporulation, and sexual development (Colot et al, 2006; Carrillo et al, 2017)
One of them is ada-6 (NCU04866), whose deletion resulted in slower growth, dramatic reduction in conidiation and female infertility (Colot et al, 2006)
Summary
Conidial production is critical for reproduction, dispersal and survival in many filamentous fungi. Sexual reproduction is a key feature that distinguishes eukaryotic organisms from prokaryotic organisms. It produces better-adapted progenies by driving genetic recombination and eliminating deleterious mutations (Ni et al, 2011; Heitman et al, 2013). 25% predicted genes in the genome of N. crassa are differentially expressed during conidiation (Greenwald et al, 2010), as well as during sexual development (Lehr et al, 2014). Identification of transcription factors, which are crucial to conidial and sexual development, and characterization of their mechanisms are critical steps toward deeper understanding of how fungal morphogenesis is regulated
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