Abstract
Fungal sexual development requires the involvement of a large number of functional genes. Fungal genes encoding sexual differentiation process proteins (SDPs), isps, have been known for decades. isp4/SDP and its homologs function as oligopeptide transporters (OPTs), yet their roles in reproduction are unknown. Here, we genetically analyzed all four isp4/SDP homologs in the sexual species Chaetomium thermophilum and asexual species Thermomyces lanuginosus. Using single gene deletion mutants, we found that T. lanuginosus SDP (TlSDP) participated in asexual sporulation, whereas the other homologs participated in sexual morphogenesis. In complementary tests, C. thermophilum SDPs (CtSDP1-3) restored sporulation defects in TlSDP deletion strains (ΔTlSDP), and their translated proteins, which were localized onto the cytomembrane, possessed OPT activity. Interestingly, CtSDP2 accumulated at the top of the hyphae played a distinct role in determining the sexual cycle, glutathione transport, and lifespan shortening. A unique 72nt-insertion fragment (72INS) was discovered in CtSDP2. Biological analysis of the 72INS deletion and DsRED-tagged fusion strains implied the involvement of 72INS in fungal growth and development. In contrast to TlSDP, which only contributes to conidial production, the three CtSDPs play important roles in sexual and asexual reproduction, and CtSDP2 harbors a unique functional 72INS that initiates sexual morphogenesis.
Highlights
Ascomycota, the largest fungal phylum, is mostly defined according to sexual morphological features, the sexual structures in which ascospores are formed (Cavalier-Smith, 2010)
Thermomyces lanuginosus strain 9W and Chaetomium thermophilum strain S4 were isolated from a sample of cow dung compost (CDC) in Jilin province, which is located in northeastern China
We found that sexual reproduction in C. thermophilum and asexual reproduction in T. lanuginosus were often found in the same samples (Figure 1A and Table 1)
Summary
Ascomycota, the largest fungal phylum, is mostly defined according to sexual morphological features, the sexual structures in which ascospores are formed (Cavalier-Smith, 2010). Sexual and asexual reproduction are common in ascomycota to produce offspring, but they have completely different features. Conidia are generally created from the Involvement of Four isp4/SDPs in Fungal Development tips of conidiophores, which are morphologically similar to vegetative hyphae. Sexual reproduction of fungi is quite complex. Aggregation of vegetative mycelia indicates the initiation of sexual reproduction. Sexual reproduction can be triggered in supposedly asexual fungi, such as Candida albicans and Trichoderma reesei (Taylor et al, 1999; Magee and Magee, 2004; Seidl et al, 2009; Dyer and O’Gorman, 2011; Dyer and O’Gorman, 2012). Penicillium chrysogenum, which has been considered asexual for more than 100 years, has been shown to reproduce sexually based on MAT gene organization (Böhm et al, 2013)
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