Fungal Secondary Metabolites and Small RNAs Enhance Pathogenicity during Plant-Fungal Pathogen Interactions

Intricacies of plants' innate immune responses and their dynamic relationship with fungi: A review

The role of the plant innate immune system in the defense and symbiosis processes becomes integral in a complex network of interactions between plants and fungi. An understanding of the molecular characterization of the plant innate immune system is crucial because it constitutes plants' self-defense shield against harmful fungi, while creating mutualistic relationships with beneficial fungi. Due to the plant-induced awareness and their complexity of interaction with fungi, sufficient assessment of the participation of the plant innate immune system in ecological balance, agriculture, and maintenance of an infinite ecosystem is mandatory. Given the current global challenge, such as the surge of plant-infectious diseases, and pursuit of sustainable forms of agriculture; it is imperative to understand the molecular language of communication between plants and fungi. That knowledge can be practically used in diverse areas, e.g., in agriculture, new tactics may be sought after to try new methods that boost crop receptiveness against fungal pathogens and reduce the dependence on chemical management. Also, it could boost sustainable agricultural practices via enhancing mycorrhizal interactions that promote nutrient absorption and optimum cropping with limited exposure of environmental contamination. Moreover, this review offers insights that go beyond agriculture and can be manipulated to boost plant conservation, environmental restoration, and quality understanding of host-pathogen interactions. Consequently, this specific review paper has offered a comprehensive view of the complex plant innate immune-based responses with fungi and the mechanisms in which they interact.

Characterization of Metabolite Landscape Distinguishes Medicinal Fungus Cordyceps sinensis and other Cordyceps by UHPLC-Q Exactive HF-X Untargeted Metabolomics

Cordyceps represent a valuable class of medicinal fungi with potential utilization. The overexploitation and resource scarcity of Cordyceps sinensis (CS) have led to the emergence of Cordyceps such as Cordyceps militaris (CM) and Cordyceps cicadae (CC) as substitutes. The medicinal value of CS is often considered superior to other Cordyceps, potentially owing to differences in active ingredients. This study aimed to evaluate the differences in the composition and abundance of the primary and secondary metabolites of CS and its substitutes by untargeted metabolomics. A total of 4671 metabolites from 18 superclasses were detected. CS and its substitutes were rich in amino acids, lipids, organic acids, and their derivatives. We statistically analyzed the metabolites and found a total of 285 differential metabolites (3'-Adenylic acid, O-Adipoylcarnitine, L-Dopachrome, etc.) between CS and CC, CS and CM, and CM and CC, which are potential biomarkers. L-glutamate and glycerophospholipids were differential metabolites. A KEGG enrichment analysis indicated that the tyrosine metabolic pathway and tryptophan metabolism pathway are the most differentially expressed pathways among the three Cordyceps. In contrast, CS was enriched in a higher abundance of most lipid metabolites when compared to CM and CC, which may be an indispensable foundation for the pharmacological functions of CS. In conclusion, systematic, untargeted metabolomics analyses for CS and other Cordyceps have delivered a precious resource for insights into metabolite landscapes and predicted potential components of disease therapeutics.

Fungal BGCs for Production of Secondary Metabolites: Main Types, Central Roles in Strain Improvement, and Regulation According to the Piano Principle

Filamentous fungi are one of the most important producers of secondary metabolites. Some of them can have a toxic effect on the human body, leading to diseases. On the other hand, they are widely used as pharmaceutically significant drugs, such as antibiotics, statins, and immunosuppressants. A single fungus species in response to various signals can produce 100 or more secondary metabolites. Such signaling is possible due to the coordinated regulation of several dozen biosynthetic gene clusters (BGCs), which are mosaically localized in different regions of fungal chromosomes. Their regulation includes several levels, from pathway-specific regulators, whose genes are localized inside BGCs, to global regulators of the cell (taking into account changes in pH, carbon consumption, etc.) and global regulators of secondary metabolism (affecting epigenetic changes driven by velvet family proteins, LaeA, etc.). In addition, various low-molecular-weight substances can have a mediating effect on such regulatory processes. This review is devoted to a critical analysis of the available data on the "turning on" and "off" of the biosynthesis of secondary metabolites in response to signals in filamentous fungi. To describe the ongoing processes, the model of "piano regulation" is proposed, whereby pressing a certain key (signal) leads to the extraction of a certain sound from the "musical instrument of the fungus cell", which is expressed in the production of a specific secondary metabolite.

The Chromosome-Scale Genomes of Exserohilum rostratum and Bipolaris zeicola Pathogenic Fungi Causing Rice Spikelet Rot Disease

Rice spikelet rot disease occurs mainly in the late stages of rice growth. Pathogenicity and biological characteristics of the pathogenic fungus and the infestation site have been the primary focus of research on the disease. To learn more about the disease, we performed whole-genome sequencing of Exserohilum rostratum and Bipolaris zeicola for predicting potentially pathogenic genes. The fungus B. zeicola was only recently identified in rice.We obtained 16 and 15 scaffolds down to the chromosome level for E. rostratum LWI and B. zeicola LWII, respectively. The length of LWI strain was approximately 34.05 Mb, and the G + C content of the whole genome was 50.56%. The length of the LWII strain was approximately 32.21 Mb, and the G + C content of the whole genome was 50.66%. After the prediction and annotation of E. rostratum LWI and B. zeicola LWII, we predicted that the LWI strain and LWII strain contain 8 and 13 potential pathogenic genes, respectively, which may be related to rice infection. These results improve our understanding of the genomes of E. rostratum and B. zeicola and update the genomic databases of these two species. It benefits subsequent studies on the mechanisms of E. rostratum and B. zeicola interactions with rice and helps to develop efficient control measures against rice spikelet rot disease.