Young-Su Seo

The oxidative stress response is required for plant pathogens to endure host-derived oxidative stress during infection. Previously, we identified the eight transcription factors (TFs) involved in the oxidative stress response in the plant pathogenic fungus Fusarium graminearum and found that of these TFs, the deletion of FgbZIP007 caused hypersensitivity to oxidative stress. However, the underlying mechanisms of Fgbzip007 are not fully understood. Based on chromatin immunoprecipitation followed by sequencing (ChIP-seq) analysis, we found the regulons of Fgbzip007, and further genetic studies demonstrated that Fgbzip007 is a key regulator for sulfur assimilation. The deletion strains of FgbZIP007 and its regulons exhibited low level of glutathione biosynthesis, which led to characterize glutathione biosynthesis. Fgbzip007-mediated sulfur assimilation is required for glutathione biosynthesis, which is essential for oxidative stress resistance and pathogenicity in F. graminearum . Although the reduced resistance of glutathione-deficient mutants against oxidative stress was restored by overexpression of FCA7 , encoding a core peroxidase, but not on pathogenicity, suggesting that glutathione in pathogenesis is independent of antioxidant properties. This study characterized the function of genes of glutathione biosynthesis, provides specific insight into how Fgbzip007 regulates pathogenesis in F. graminearum , and establishes a genetic framework for the molecular dissection of a TF Fgbzip007 with the integration of pathogen responses to oxidative stress. IMPORTANCE Fusarium graminearum is a destructive fungal pathogen that causes Fusarium head blight (FHB) on a wide range of cereal crops. To control fungal diseases, it is essential to comprehend the pathogenic mechanisms that enable fungi to overcome host defenses during infection. Pathogens require an oxidative stress response to overcome host-derived oxidative stress. Here, we identify the underlying mechanisms of the Fgbzip007-mediated oxidative stress response in F. graminearum . ChIP-seq and subsequent genetic analyses revealed that the role of glutathione in pathogenesis is not dependent on antioxidant functions in F. graminearum . Altogether, this study establishes a comprehensive framework for the Fgbzip007 regulon on pathogenicity and oxidative stress responses, offering a new perspective on the role of glutathione in pathogenicity.

Members of the genus Chryseobacterium have attracted great interest as beneficial bacteria that can promote plant growth and biocontrol. Given the recent risks of climate change, it is important to develop tolerance strategies for efficient applications of plant-beneficial bacteria in saline environments. However, the genetic determinants of plant-growth-promoting and halotolerance effects in Chryseobacterium have not yet been investigated at the genomic level. Here, a comparative genomic analysis was conducted with seven Chryseobacterium species. Phylogenetic and phylogenomic analyses revealed niche-specific evolutionary distances between soil and freshwater Chryseobacterium species, consistent with differences in genomic statistics, indicating that the freshwater bacteria have smaller genome sizes and fewer genes than the soil bacteria. Phosphorus- and zinc-cycling genes (required for nutrient acquisition in plants) were universally present in all species, whereas nitrification and sulphite reduction genes (required for nitrogen- and sulphur-cycling, respectively) were distributed only in soil bacteria. A pan-genome containing 6842 gene clusters was constructed, which reflected the general features of the core, accessory and unique genomes. Halotolerant species with an accessory genome shared a Kdp potassium transporter and biosynthetic pathways for branched-chain amino acids and the carotenoid lycopene, which are associated with countermeasures against salt stress. Protein–protein interaction network analysis was used to define the genetic determinants of Chryseobacterium salivictor NBC122 that reduce salt damage in bacteria and plants. Sixteen hub genes comprised the aromatic compound degradation and Por secretion systems, which are required to cope with complex stresses associated with saline environments. Horizontal gene transfer and CRISPR–Cas analyses indicated that C. salivictor NBC122 underwent more evolutionary events when interact