Plant defense compound triggers mycotoxin synthesis by regulating H2B ub1 and H3K4 me2/3 deposition

Comparative transcriptome analysis of Fusarium graminearum challenged with distinct fungicides and functional analysis of FgICL gene

Fusarium graminearum is an economically important phytopathogenic fungus. Chemical control remains the dominant approach to managing this plant pathogen. In the present study, we performed a comparative transcriptome analysis to understand the effects of four commercially used fungicides on F. graminearum. The results revealed a significant number of differentially expressed genes related to carbohydrate, amino acid, and lipid metabolism, particularly in the carbendazim and phenamacril groups. Central carbon pathways, including the TCA and glyoxylate cycles, were found to play crucial roles across all treatments except tebuconazole. Weighted gene co-expression network analysis reinforced the pivotal role of central carbon pathways based on identified hub genes. Additionally, critical candidates associated with ATP-binding cassette transporters, heat shock proteins, and chitin synthases were identified. The crucial functions of the isocitrate lyase in F. graminearum were also validated. Overall, the study provided comprehensive insights into the mechanisms of how F. graminearum responds to fungicide stress.

Progress on H2B as a multifunctional protein related to pathogens

Histone H2B is a member of the core histones, which together with other histones form the nucleosome, the basic structural unit of chromosomes. As scientists delve deeper into histones, researchers gradually realize that histone H2B is not only an important part of nucleosomes, but also plays a momentous role in regulating gene transcription, acting as a receptor and antimicrobial action outside the nucleus. There are a variety of epigenetically modified sites in the H2B tail rich in arginine and lysine, which can occur in ubiquitination, phosphorylation, methylation, acetylation, etc. When stimulated by foreign factors such as bacteria, viruses or parasites, histone H2B can act as a receptor for the recognition of these pathogens, and induce an intrinsic immune response to enhance host defense. In addition, the extrachromosomal histone H2B is also an important anti-microorganism agent, which may be the key to the development of antibiotics in the future. This review aims to summarize the interaction between histone H2B and etiological agents and explore the role of H2B in epigenetic modifications, receptors and antimicrobial activity.

Regulation of nitrogen utilization and mycotoxin biosynthesis by the GATA transcription factor AaAreA in Alternaria alternata

Alternaria alternata is a prevalent postharvest pathogen that generates diverse mycotoxins, notably alternariol (AOH) and alternariol monomethyl ether (AME), which are recurrent severe contaminants. Nitrogen sources modulate fungal growth, development, and secondary metabolism, including mycotoxin production. The GATA transcription factor AreA regulates nitrogen source utilization. However, little is known about its involvement in the regulation of nitrogen utilization in A. alternata. To examine the regulatory mechanism of AaAreA on AOH and AME biosynthesis in A. alternata, we analyzed the impact of diverse nitrogen sources on the fungal growth, conidiation and mycotoxin production. The use of a secondary nitrogen source (NaNO3) enhanced mycelial elongation and sporulation more than the use of a primary source (NH4Cl). NaNO3 favored greater mycotoxin accumulation than did NH4Cl. The regulatory roles of AaAreA were further clarified through gene knockout. The absence of AaAreA led to an overall reduction in growth in minimal media containing any nitrogen source except NH4Cl. AaAreA positively regulates mycotoxin biosynthesis when both NH4Cl and NaNO3 are used as nitrogen sources. Subcellular localization analysis revealed abundant nuclear transport when NaNO3 was the sole nitrogen source. The regulatory pathway of AaAreA was systematically revealed through comprehensive transcriptomic analyses. The deletion of AaAreA significantly impedes the transcription of mycotoxin biosynthetic genes, including aohR, pksI and omtI. The interaction between AaAreA and aohR, a pathway-specific transcription factor gene, demonstrated that AaAreA binds to the aohR promoter sequence (5'-GGCTATGGAAA-3'), activating its transcription. The expressed AohR regulates the expression of downstream synthase genes in the cluster, ultimately impacting mycotoxin production. This study provides valuable information to further understand how AreA regulates AOH and AME biosynthesis in A. alternata, thereby enabling the effective design of control measures for mycotoxin contamination.

Evaluation of the Growth, Sporulation, Fungicide Efficacy, and Host Range of Ramularia sphaeroidea

Ramularia sphaeroidea was primarily identified based on the characteristics of its conidia and several sequences. The fungus causes severe leaf spot disease on hairy vetch (Vicia villosa var. glabrescens) in Yunnan Province in China. The growth, sporulation, fungicide efficacy, and host range of the pathogen were evaluated to aid in disease management. Different types of culture media and carbon and nitrogen sources were used to evaluate the growth of R. sphaeroidea. Oatmeal, maltose, and potassium nitrate agar had a higher amount of sporulation. Difenoconazole (10%) was the most effective fungicide against the leaf disease caused by R. sphaeroidea. In addition, foliar inoculation sprays were used to assess the host range of R. sphaeroidea in six different plant species, including alfalfa (Medicago sativa L.), sainfoin (Onobrychis viciifolia Scop.), erect milkvetch (Astragalus adsurgens Pall.), common vetch (Vicia sativa L.), red clover (Trifolium pratense L.), and white clover (Trifolium repens L.). R. sphaeroidea successfully infected these plants, indicating that it has a wider host range than hairy vetches.

Advances in Understanding Fusarium graminearum: Genes Involved in the Regulation of Sexual Development, Pathogenesis, and Deoxynivalenol Biosynthesis

The wheat head blight disease caused by Fusarium graminearum is a major concern for food security and the health of both humans and animals. As a pathogenic microorganism, F. graminearum produces virulence factors during infection to increase pathogenicity, including various macromolecular and small molecular compounds. Among these virulence factors, secreted proteins and deoxynivalenol (DON) are important weapons for the expansion and colonization of F. graminearum. Besides the presence of virulence factors, sexual reproduction is also crucial for the infection process of F. graminearum and is indispensable for the emergence and spread of wheat head blight. Over the last ten years, there have been notable breakthroughs in researching the virulence factors and sexual reproduction of F. graminearum. This review aims to analyze the research progress of sexual reproduction, secreted proteins, and DON of F. graminearum, emphasizing the regulation of sexual reproduction and DON synthesis. We also discuss the application of new gene engineering technologies in the prevention and control of wheat head blight.

COMPASS core subunits MpSet1 and MpSwd3 regulate Monascus pigments synthesis in Monascus purpureus

In eukaryotes, methylation of histone H3 at lysine 4 (H3K4me) catalyzed by the complex of proteins associated with Set1 (COMPASS) is crucial for the transcriptional regulation of genes and the development of organisms. In Monascus, the functions of COMPASS in establishing H3K4me remain unclear. This study first identified the conserved COMPASS core subunits MpSet1 and MpSwd3 in Monascus purpureus and confirmed their roles in establishing H3K4me2/3. Loss of MpSet1 and MpSwd3 resulted in slower growth and development and inhibited the formation of cleistothecia, ascospores, and conidia. The loss of these core subunits also decreased the production of extracellular and intracellular Monascus pigments (MPs) by 94.2%, 93.5%, 82.7%, and 82.5%, respectively. In addition, RNA high-throughput sequencing and quantitative real-time polymerase chain reaction (qRT-PCR) showed that the loss of MpSet1 and MpSwd3 altered the expression of 2646 and 2659 genes, respectively, and repressed the transcription of MPs synthesis-related genes. In addition, the ΔMpset1 and ΔMpswd3 strains demonstrated increased sensitivity to cell wall stress with the downregulation of chitin synthase-coding genes. These results indicated that the COMPASS core subunits MpSet1 and MpSwd3 help establish H3K4me2/3 for growth and development, spore formation, and pigment synthesis in Monascus. These core subunits also assist in maintaining cell wall integrity.

HapX-mediated H2B deub1 and SreA-mediated H2A.Z deposition coordinate in fungal iron resistance

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.

The Phosphatase Cascade Nem1/Spo7-Pah1 Regulates Fungal Development, Lipid Homeostasis, and Virulence in Botryosphaeria dothidea

Protein phosphatase complex Nem1/Spo7 plays crucial roles in the regulation of various biological processes in eukaryotes. However, its biological functions in phytopathogenic fungi are not well understood. In this study, genome-wide transcriptional profiling analysis revealed that Nem1 was significantly upregulated during the infection process of Botryosphaeria dothidea, and we identified and characterized the phosphatase complex Nem1/Spo7 and its substrate Pah1 (a phosphatidic acid phosphatase) in B. dothidea. Nem1/Spo7 physically interacted with and dephosphorylated Pah1 to promote triacylglycerol (TAG) and subsequent lipid droplet (LD) synthesis. Moreover, the Nem1/Spo7-dependently dephosphorylated Pah1 functioned as a transcriptional repressor of the key nuclear membrane biosynthesis genes to regulate nuclear membrane morphology. In addition, phenotypic analyses showed that the phosphatase cascade Nem1/Spo7-Pah1 was involved in regulating mycelial growth, asexual development, stress responses, and virulence of B. dothidea. IMPORTANCE Botryosphaeria canker and fruit rot caused by the fungus Botryosphaeria dothidea is one of the most destructive diseases of apple worldwide. Our data indicated that the phosphatase cascade Nem1/Spo7-Pah1 plays important roles in the regulation of fungal growth, development, lipid homeostasis, environmental stress responses, and virulence in B. dothidea. The findings will contribute to the in-depth and comprehensive understanding of Nem1/Spo7-Pah1 in fungi and the development of target-based fungicides for disease management.

Multiple chromatin-associated modules regulate expression of an intracellular immune receptor gene in Arabidopsis

The expression of an intracellular immune receptor gene SNC1 (SUPPRESSOR OF npr1, CONSTITUTIVE 1) is regulated by multiple chromatin-associated proteins for tuning immunity and growth in Arabidopsis. Whether and how these regulators coordinate to regulate SNC1 expression under varying environmental conditions is not clear. Here, we identified two activation and one repression regulatory modules based on genetic and molecular characterizations of five chromatin-associated regulators of SNC1. Modifier of snc1 (MOS1) constitutes the first module and is required for the interdependent functions of ARABIDOPSIS TRITHORAX-RELATED 7 (ATXR7) and HISTONE MONOUBIQUITINATION 1 (HUB1) to deposit H3K4me3 and H2Bub1 at the SNC1 locus. CHROMATIN REMODELING 5 (CHR5) constitutes a second module and works independently of ATXR7 and HUB1 in the MOS1 module. HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 15 (HOS15) constitutes a third module responsible for removing H3K9ac to repress SNC1 expression under nonpathogenic conditions. The upregulation of SNC1 resulting from removing the HOS15 repression module is partially dependent on the function of the CHR5 module and the MOS1 module. Together, this study reveals both the distinct and interdependent regulatory mechanisms at the chromatin level for SNC1 expression regulation and highlights the intricacy of regulatory mechanisms of NLR expression under different environment.

Transcriptome Profile of Fusarium graminearum Treated by Putrescine

Fusarium graminearum (F. graminearum) is the main pathogen of Fusarium head blight (FHB) in wheat, barley, and corn. Deoxynivalenol (DON), produced by F. graminearum, is the most prevalent toxin associated with FHB. The wheat defense compound putrescine can promote DON production during F. graminearum infection. However, the underlying mechanisms of putrescine-induced DON synthesis are not well-studied. To investigate the effect of putrescine on the global transcriptional regulation of F. graminearum, we treated F. graminearum with putrescine and performed RNA deep sequencing. We found that putrescine can largely affect the transcriptome of F. graminearum. Gene ontology (GO) and KEGG enrichment analysis revealed that having a large amount of DEGs was associated with ribosome biogenesis, carboxylic acid metabolism, glycolysis/gluconeogenesis, and amino acid metabolism pathways. Co-expression analysis showed that 327 genes had similar expression patterns to FgTRI genes and were assigned to the same module. In addition, three transcription factor genes were identified as hub genes in this module, indicating that they may play important roles in DON synthesis. These results provide important clues for further analysis of the molecular mechanisms of putrescine-induced DON synthesis and will facilitate the study of the pathogenic mechanisms of FHB.

The roles of epigenetic modifications in the regulation of auxin biosynthesis

Auxin is one of the most important plant growth regulators of plant morphogenesis and response to environmental stimuli. Although the biosynthesis pathway of auxin has been elucidated, the mechanisms regulating auxin biosynthesis remain poorly understood. The transcription of auxin biosynthetic genes is precisely regulated by complex signaling pathways. When the genes are expressed, epigenetic modifications guide mRNA synthesis and therefore determine protein production. Recent studies have shown that different epigenetic factors affect the transcription of auxin biosynthetic genes. In this review, we focus our attention on the molecular mechanisms through which epigenetic modifications regulate auxin biosynthesis.