Huang, J.-W. | bioRxiv Science

bioRxiv2020

Degenerated virulence and irregular development of Fusarium oxysporum f. sp. niveum induced by successive subculture

Successive cultivation of fungus has been reported to cause the sectorization, which leads to degeneration of developmental phenotype, and virulence. Fusarium oxysporum f. sp. niveum (Fon), the causal agent of watermelon Fusarium wilt, demonstrated that successive cultivation formed the degenerated sectors. In the present research, we demonstrated that subculture with aged mycelium increased the incidence of degenerations. To further investigate the differences between the Fon wild type (sporodochial type, ST) and variants (MT: mycelium type and PT: pionnotal type), developmental phenotypes and pathogenicity to watermelon were examined. Results have shown that degeneration variants (PT2, PT3, PT11 and MT6) were different from ST with mycelium growth, conidia production and chlamydospore formation. Virulence of degenerated variants on susceptible watermelon Grand Baby (GB) cultivar was determined after inoculated with Fon variants and Fon ST. In root dipping methods, all Fon variants showed slightly increased disease severity than ST. Conversely, all Fon variants showed a significant decrease in disease progression compared with ST through infested soil inoculation. The contrary results of two inoculation methods suggest that the changes of successive cultural degeneration may lead to the loss of pathogen virulence-related factors of the early stage of Fon infection process. Therefore, Cell wall-degrading enzymes (CWDEs; cellulase, pectinase, and xylanase) activities of different variants were analysed. All Fon degenerated variants demonstrated significantly decreased of CWDEs activities compared with ST. Additionally, transcripts level of 9 virulence-related genes (fmk1, fgb1, pacC, xlnR, pl1, rho1, gas1, wc1 and fow1) were assessed in normal state. The degenerated variants demonstrated a significantly low level of tested virulence-related genes transcripts except for fmk1, xlnR and fow1. In summary, the degeneration of Fon is triggered with successive subculture through aged mycelium. The degeneration showed significant impacts on virulence to watermelon, which caused by the reduction of CWDEs activities and declining expression of a set of virulence-related genes.

microbiology↗

bioRxiv2019

Identification of MCM8IP, an interactor of MCM8-9 and RPA1 that promotes homologous recombination and DNA synthesis in response to DNA damage

Homologous recombination (HR) mediates the error-free repair of DNA double-strand breaks to maintain genomic stability. HR is carried out by a complex network of DNA repair factors. Here we identify C17orf53/MCM8IP, an OB-fold containing protein that binds ssDNA, as a novel DNA repair factor involved in HR. MCM8IP-deficient cells exhibit HR defects, especially in long-tract gene conversion, occurring downstream of RAD51 loading, consistent with a role for MCM8IP in HR-dependent DNA synthesis. Moreover, loss of MCM8IP confers cellular sensitivity to crosslinking agents and PARP inhibition. Importantly, we identify a direct interaction with MCM8-9, a putative helicase complex mutated in Primary Ovarian Insufficiency, that is crucial for MCM8IPs ability to promote resistance to DNA damaging agents. In addition to its association with MCM8-9, MCM8IP also binds directly to RPA1. We show that the interactions of MCM8IP with both MCM8-9 and RPA are required to maintain replication fork progression in response to treatment with crosslinking agents. Collectively, our work identifies MCM8IP as a key regulator of DNA damage-associated DNA synthesis during DNA recombination and replication.

genetics↗