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  1. Abstract

    Plant pathogens are challenged by host-derived iron starvation or excess during infection, but the mechanism through which pathogens counteract iron stress is unclear. Here, we found that Fusarium graminearum encounters iron excess during the colonization of wheat heads. Deletion of heme activator protein X (FgHapX), siderophore transcription factor A (FgSreA) or both attenuated virulence. Further, we found that FgHapX activates iron storage under iron excess by promoting histone H2B deubiquitination (H2B deub1) at the promoter of the responsible gene. Meanwhile, FgSreA is shown to inhibit genes mediating iron acquisition during iron excess by facilitating the deposition of histone variant H2A.Z and histone 3 lysine 27 trimethylation (H3K27 me3) at the first nucleosome after the transcription start site. In addition, the monothiol glutaredoxin FgGrx4 is responsible for iron sensing and control of the transcriptional activity of FgHapX and FgSreA via modulation of their enrichment at target genes and recruitment of epigenetic regulators, respectively. Taken together, our findings elucidated the molecular mechanisms for adaptation to iron excess mediated by FgHapX and FgSreA during infection in F. graminearum and provide novel insights into regulation of iron homeostasis at the chromatin level in eukaryotes.

     
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  2. Summary

    SUMOylation as one of the protein post‐translational modifications plays crucial roles in multiple biological processes of eukaryotic organisms.Botrytis cinereais a devastating fungal pathogen and capable of infecting plant hosts at low temperature. However, the molecular mechanisms of low‐temperature adaptation are largely unknown in fungi.

    Combining with biochemical methods and biological analyses, we report that SUMOylation regulates pathogen survival at low temperature and oxidative DNA damage response during infection inB. cinerea. The heat shock protein (Hsp70) BcSsb and E3 ubiquitin ligase BcRad18 were identified as substrates of SUMOylation; moreover, their SUMOylation both requires a single unique SUMO‐interacting motif (SIM).

    SUMOylated BcSsb regulates β‐tubulin accumulation, thereby affecting the stability of microtubules and consequently mycelial growth at low temperature. On the contrary, SUMOylated BcRad18 modulates mono‐ubiquitination of the sliding clamp protein proliferating cell nuclear antigen (PCNA), which is involved in response to oxidative DNA damage during infection.

    Our study uncovers the molecular mechanisms of SUMOylation‐mediated low‐temperature survival and oxidative DNA damage tolerance during infection in a devastating fungal pathogen, which provides novel insights into low‐temperature adaptation and pathogenesis for postharvest pathogens as well as new targets for inhibitor invention in disease control.

     
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