Calcium signaling is involved in diverse cellular processes in fungi

Integration of fungal transcriptomics and metabolomics provides insights into the early interaction between the ORM fungus Tulasnella sp. and the orchid Serapias vomeracea seeds

In nature, germination of orchid seeds and early plant development rely on a symbiotic association with orchid mycorrhizal (ORM) fungi. These fungi provide the host with the necessary nutrients and facilitate the transition from embryos to protocorms. Despite recent advances in omics technologies, our understanding of this symbiosis remains limited, particularly during the initial stages of the interaction. To address this gap, we employed transcriptomics and metabolomics to investigate the early responses occurring in the mycorrhizal fungus Tulasnella sp. isolate SV6 when co-cultivated with orchid seeds of Serapias vomeracea. The integration of data from gene expression and metabolite profiling revealed the activation of some fungal signalling pathways before the establishment of the symbiosis. Prior to seed contact, an indole-related metabolite was produced by the fungus, and significant changes in the fungal lipid profile occurred throughout the symbiotic process. Additionally, the expression of plant cell wall-degrading enzymes (PCWDEs) was observed during the pre-symbiotic stage, as the fungus approached the seeds, along with changes in amino acid metabolism. Thus, the dual-omics approach employed in this study yielded novel insights into the symbiotic relationship between orchids and ORM fungi and suggest that the ORM fungus responds to the presence of the orchid seeds prior to contact.

The MAP kinase FvHog1 regulates FB1 synthesis and Ca2+ homeostasis in Fusarium verticillioides

The high osmolarity glycerol 1 mitogen-activated protein kinase (Hog1-MAPK) cascade genes are important for diverse biological processes. The activated Hog1 upon multiple environmental stress stimuli enters into the nucleus where it directly phosphorylates transcription factors to regulate various physiological processes in phytopathogenic fungi. However, their roles have not been well-characterized in Fusarium verticillioides. In this study, FvHog1 is identified and functionally analyzed. The findings reveal that the phosphorylation level and nuclear localization of FvHog1 are increased in Fumonisin B1 (FB1)-inducing condition to regulate the expression of FB1 biosynthesis FUM genes. More importantly, the deletion mutants of Hog1-MAPK pathway show increased sensitivity to Ca2+ stress and elevated intracellular Ca2+ content. The phosphorylation level and nuclear localization of FvHog1 are increased with Ca2+ treatment. Furthermore, our results show that FvHog1 can directly phosphorylate Ca2+-responsive zinc finger transcription factor 1 (FvCrz1) to regulate Ca2+ homeostasis. In conclusion, our findings indicate that FvHog1 is required for FB1 biosynthesis, pathogenicity and Ca2+ homeostasis in F. verticillioides. It provides a theoretical basis for effective prevention and control maize ear and stalk rot disease.

Methods for the detection of intracellular calcium in filamentous fungi

Calcium (Ca2+), a critical secondary messenger, is also known as the molecule of life and death. The cell responds to a minute change in Ca2+ concentration and tightly maintains Ca2+ homeostasis. Therefore, determining the cell Ca2+ level is critical to understand Ca2+ distribution in the cell and various cell processes. Many techniques have been developed to measure Ca2+ in the cell. We review here different methods used to detect and measure Ca2+ in filamentous fungi. Ca2+-sensitive fluorescent chlortetracycline hydrochloride (CTC), Ca2+-selective microelectrode, Ca2+ isotopes, aequorins, and RGECOs are commonly used to measure the Ca2+ level in filamentous fungi. The use of CTC was one of the earliest methods, developed in 1988, to measure the Ca2+ gradient in the filamentous fungus Neurospora crassa. Subsequently, Ca2+-specific microelectrodes were developed later in the 1990s to identify Ca2+ ion flux variations, and to measure Ca2+ concentration. Another method for quantifying Ca2+ is by using radio-labeled Ca2+ as a tracer. The usage of 45Ca to measure Ca2+ in Saccharomyces cerevisiae was reported previously and the same methodology was also used to detect Ca2+ in N. crassa recently. Subsequently, genetically engineered Ca2+ indicators (GECIs) like aequorins and RGECOs have been developed as Ca2+ indicators to detect and visualize Ca2+ inside the cell. In this review, we summarize various methodologies used to detect and measure Ca2+ in filamentous fungi with their advantages and limitations. •Chlortetracycline (CTC) fluorescence assay is used for visualizing Ca2+ level, whereas microelectrodes technique is used to determine Ca2+ flux in the cell.•Radioactive 45Ca is useful for quantification of Ca2+ in the cellular compartments.•Genetically modified calcium indicators (GECIs) are used to study Ca2+ dynamics in the cell.

Performance of Metarhizium rileyi Nm017: nutritional supplementation to improve production and quality conidia

This study aimed to analyze the effect of nutritional supplements on improving conidia production of Metarhizium rileyi Nm017 at laboratory scale (yields of conidia/substrate and biomass/substrate, and substrate consumption). Also, the influence on quality parameters were evaluated (germination at 36 and 48 h, enzymatic activity, and insecticidal activity on Helicoverpa zea). Six treatments (T1-T6) were assessed and all of them reached maximum conidia concentration after 7 days fermentation, a feasible production timetable. Yields from treatment T6 (yeast extract + V8 juice) were 1.5-threefold higher than the other treatments. Conidia from T6 reached germinations of 56% and 12% at 36 and 48 h, respectively, higher than T1 (without supplements), which had the lowest values found. M. rileyi conidia obtained from treatment T6 had the highest enzymatic activity (0.45 U chitinase g-1, 0.28 U lipase g-1, and 1.29 U protease g-1). However, treatments with the highest conidia yields and enzymatic activity were not positively correlated to the efficacy against H. zea. When M. rileyi was produced on T5 (yeast hydrolysate + V8 juice), conidia were 35% more virulent than treatment T6. The findings evidenced the noticeable impact of nutritional substrate amended for conidia production and quality. This work showed the relevance of insecticidal activity assessment as a selection criterion in the mass production development of a biocontrol agent.

A phylogenomic perspective on interspecific competition

Evolutionary processes may have substantial impacts on community assembly, but evidence for phylogenetic relatedness as a determinant of interspecific interaction strength remains mixed. In this perspective, we consider a possible role for discordance between gene trees and species trees in the interpretation of phylogenetic signal in studies of community ecology. Modern genomic data show that the evolutionary histories of many taxa are better described by a patchwork of histories that vary along the genome rather than a single species tree. If a subset of genomic loci harbour trait-related genetic variation, then the phylogeny at these loci may be more informative of interspecific trait differences than the genome background. We develop a simple method to detect loci harbouring phylogenetic signal and demonstrate its application through a proof-of-principle analysis of Penicillium genomes and pairwise interaction strength. Our results show that phylogenetic signal that may be masked genome-wide could be detectable using phylogenomic techniques and may provide a window into the genetic basis for interspecific interactions.

Deconstructing the Dimensions of Mycobiome Fingerprints in Luohandu Cave, Guilin, Southern China

Subterranean karst caves are windows into the terrestrial subsurface to deconstruct the dimensions of mycobiome fingerprints. However, impeded by the constraints of remote locations, the inaccessibility of specimens and technical limitations, the mycobiome of subterranean karst caves has remained largely unknown. Weathered rock and sediment samples were collected from Luohandu cave (Guilin, Southern China) and subjected to Illumina Hiseq sequencing of ITS1 genes. A total of 267 known genera and 90 known orders in 15 phyla were revealed in the mycobiomes. Ascomycota dominated all samples, followed by Basidiomycota and Mortierellomycota. The sediments possessed the relatively highest alpha diversity and were significantly different from weathered rocks according to the diversity indices and richness metrics. Fifteen families and eight genera with significant differences were detected in the sediment samples. The Ca/Mg ratio appeared to significantly affect the structure of the mycobiome communities. Ascomycota appeared to exert a controlling influence on the mycobiome co-occurrence network of the sediments, while Ascomycota and Basidiomycota were found to be the main phyla in the mycobiome co-occurrence network of weathered rocks. Our results provide a more comprehensive dimension to the mycobiome fingerprints of Luohandu cave and a new window into the mycobiome communities and the ecology of subterranean karst cave ecosystems.

Bioconversion of rice straw by Lentinula edodes under different spawn formulations

To attend to the growing world demand for mushrooms, it is interesting to increase the system's productivity, improve quality and reduce production costs. This study aimed to optimize the production and quality of fruiting bodies of the edible and medicinal mushroom Lentinula edodes (shiitake), in agroresidues substrate using appropriate strain and spawn formulation. The evaluation was conducted using two strains under seven different spawn formulations (Control [C]: Sorghum grain + 2.5% CaCO3; (2) C + 2.5% sawdust; (T3) C + 5% sawdust; (T4) C + 2.5% peat; (T5) C + 5% peat; (T6) C + 1.25% sawdust + 1.25% peat; (T7) C + 2.5% sawdust + 2.5% peat) that were inoculated into the blocks at a proportion of 2% (w/w). The substrate was formulated with 63% rice straw, 20% sawdust, 15% wheat bran, and 2% CaCO3 and sterilized. The incubation period was 87 days. Two flushes were obtained. Adding small aliquots of peat and sawdust to the inoculum gave significantly higher morphological results than the control in all variables analyzed. The days required for the first harvest ranged from 87 to 94 days. The average weight of basidiomes ranged from 6.38 to 28.75 g. The productivity data show superior results for the treatments in which the spawn was supplemented with sawdust and peat. Enhanced bioconversion with supplemented spawn shows promises for yield and composition improvement, crucial for commercial viability. It can be concluded that shiitake production using agroresidues such as straw can be increased using a suitable strain/spawn for optimal production.

The cell functions of phospholipase C-1, Ca2+/H+ exchanger-1, and secretory phospholipase A2 in tolerance to stress conditions and cellulose degradation in Neurospora crassa

We investigated the cell functions of the Ca2+ signaling genes phospholipase C-1 (plc-1), Ca2+/H+ exchanger (cpe-1), and secretory phospholipase A2 (splA2) for stress responses and cellulose utilization in Neurospora crassa. The Δplc-1, Δcpe-1, and ΔsplA2 mutants displayed increased sensitivity to the alkaline pH and reduced survival during induced thermotolerance. The ΔsplA2 mutant also exhibited hypersensitivity to the DTT-induced endoplasmic reticulum (ER) stress, increased microcrystalline cellulose utilization, increased protein secretion, and glucose accumulation in the culture supernatants. Moreover, the ΔsplA2 mutant could not grow on microcrystalline cellulose during ER stress. Furthermore, plc-1, cpe-1, and splA2 synthetically regulate the acquisition of thermotolerance induced by heat shock, responses to alkaline pH and ER stress, and utilization of cellulose and other alternate carbon sources in N. crassa. In addition, expression of the alkaline pH regulator, pac-3, and heat shock proteins, hsp60, and hsp80 was reduced in the Δplc-1, Δcpe-1, and ΔsplA2 single and double mutants. The expression of the unfolded protein response (UPR) markers grp-78 and pdi-1 was also significantly reduced in the mutants showing growth defect during ER stress. The increased cellulolytic activities of the ΔsplA2 and Δcpe-1; ΔsplA2 mutants were due to increased cbh-1, cbh-2, and endo-2 expression in N. crassa. Therefore, plc-1, cpe-1, and splA2 are involved in stress responses and cellulose utilization in N. crassa.

Calmodulin, Calcium/Calmodulin-Dependent Kinases-1 and 2 Regulate Expression of the Heat Shock Proteins for Heat Shock Tolerance and Pheromone Signaling Genes for Sexual Development in Neurospora crassa

Calmodulin (CaM) is a primary Ca2+ sensor that binds and activates numerous target proteins and regulates several cellular processes in eukaryotes. CaM is essential in Neurospora crassa; therefore, we generated a CaM mutant using repeat-induced point (RIP) mutation and investigated the cmdRIP mutant phenotypes. We also studied knockout mutants of four Ca2+/CaM kinases (camk-1, 2, 3, and 4) for their role during stress conditions and sexual development. The cmdRIP, ∆camk-1, and ∆camk-2 mutants showed reduced survival and growth rates under heat stress, oxidative stress, pH, and ER stress conditions. In addition, under the heat stress conditions, expression of the heat shock protein genes hsp70 and hsp80 was reduced in the cmdRIP, ∆camk-1, and ∆camk-2 mutants. The cmdRIP mutant was also defective in cell fusion, its vegetative hyphae could not support the fertilized wild type perithecia graft, and female sterile. Furthermore, the expression of pheromone signaling genes pre-1, pre-2, ccg-4, mfa-1, and fmf-1 was reduced in the cmdRIP, ∆camk-1, and ∆camk-2 mutants. Therefore, CaM, Ca2+/CaMK-1 and 2 are involved in the tolerance to heat stress conditions and sexual development by regulating the heat shock and pheromone response pathways, respectively, in N. crassa.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-023-01091-8.

Looking outside the box: a comparative cross-kingdom view on the cell biology of the three major lineages of eukaryotic multicellular life

Many cell biological facts that can be found in dedicated scientific textbooks are based on findings originally made in humans and/or other mammals, including respective tissue culture systems. They are often presented as if they were universally valid, neglecting that many aspects differ-in part considerably-between the three major kingdoms of multicellular eukaryotic life, comprising animals, plants and fungi. Here, we provide a comparative cross-kingdom view on the basic cell biology across these lineages, highlighting in particular essential differences in cellular structures and processes between phyla. We focus on key dissimilarities in cellular organization, e.g. regarding cell size and shape, the composition of the extracellular matrix, the types of cell-cell junctions, the presence of specific membrane-bound organelles and the organization of the cytoskeleton. We further highlight essential disparities in important cellular processes such as signal transduction, intracellular transport, cell cycle regulation, apoptosis and cytokinesis. Our comprehensive cross-kingdom comparison emphasizes overlaps but also marked differences between the major lineages of the three kingdoms and, thus, adds to a more holistic view of multicellular eukaryotic cell biology.

Regulation mechanism of lipids for extracellular yellow pigments production by Monascus purpureus BWY-5

The biosynthesis and secretion of Monascus pigments are closely related to the integrity of the cell membrane, which determines the composition of lipids and its content in cell membrane. The present study aimed to thoroughly describe the changes of lipid profiling in Monascus purpureus BWY-5, which was screened by carbon ion beam irradiation (¹²C⁶⁺) to almost single yield extracellular Monascus yellow pigments (extra-MYPs), by absolute quantitative lipidomics and tandem mass tags (TMT) based quantitative proteomic. ¹²C⁶⁺ irradiation caused non-lipid oxidation damage to Monascus cell membrane, leading to an imbalance in cell membrane lipid homeostasis. This imbalance was attributed to significant changes not only in the composition but also in the content of lipids in Monascus, especially the inhibition of glycerophospholipid biosynthesis. Integrity of plasma membrane was maintained by the increased production of ergosterol, monogalactosylmonoacylglycerol (MGMG) and sulfoquinovosylmonoacylglycerol (SQMG), while mitochondrial membrane homeostasis was maintained by the increase of cardiolipin production. The growth and extra-MYPs production of Monascus BWY-5 have been regulated by the promotion of sphingolipids (ceramide and sulfatide) biosynthesis. Simultaneous, energy homeostasis may be achieved by increase of TG synthesis and Ca²⁺/Mg²⁺-ATPase activity. These finding suggest ergosterol, cardiolipin, sphingolipids, MGMG and SQMG play a key facilitating role in cytomembrane lipid homeostasis maintaining for Monascus purpureus BWY-5, and then it is closely related to cell growth and extra-MYPs production. KEY POINTS: 1. Energy homeostasis in Monascus purpureus BWY-5 was achieved by increase of TG synthesis and Ca²⁺/Mg²⁺-ATPase activity. 2. Integrity of plasma membrane in Monascus purpureus BWY-5 was maintained by the increased production of ergosterol. 3. Mitochondrial membrane homeostasis in Monascus purpureus BWY-5 was maintaed by the increase of cardiolipin synthesis.

The ER calcium channel Csg2 integrates sphingolipid metabolism with autophagy

Sphingolipids are ubiquitous components of membranes and function as bioactive lipid signaling molecules. Here, through genetic screening and lipidomics analyses, we find that the endoplasmic reticulum (ER) calcium channel Csg2 integrates sphingolipid metabolism with autophagy by regulating ER calcium homeostasis in the yeast Saccharomyces cerevisiae. Csg2 functions as a calcium release channel and maintains calcium homeostasis in the ER, which enables normal functioning of the essential sphingolipid synthase Aur1. Under starvation conditions, deletion of Csg2 causes increases in calcium levels in the ER and then disturbs Aur1 stability, leading to accumulation of the bioactive sphingolipid phytosphingosine, which specifically and completely blocks autophagy and induces loss of starvation resistance in cells. Our findings indicate that calcium homeostasis in the ER mediated by the channel Csg2 translates sphingolipid metabolism into autophagy regulation, further supporting the role of the ER as a signaling hub for calcium homeostasis, sphingolipid metabolism and autophagy.

Mechanism of Zn2+ regulation of cellulase production in Trichoderma reesei Rut-C30

BACKGROUND

Trichoderma reesei Rut-C30 is a hypercellulolytic mutant strain that degrades abundant sources of lignocellulosic plant biomass, yielding renewable biofuels. Although Zn2+ is an activator of enzymes in almost all organisms, its effects on cellulase activity in T. reesei have yet to be reported.

RESULTS

Although high concentrations of Zn2+ severely suppressed the extension of T. reesei mycelia, the application of 1-4 mM Zn2+ enhanced cellulase and xylanase production in the high-yielding cellulase-producing Rut-C30 strain of T. reesei. Expression of the major cellulase, xylanase, and two essential transcription activator genes (xyr1 and ace3) increased in response to Zn2+ stimulation. Transcriptome analysis revealed that the mRNA levels of plc-e encoding phospholipase C, which is involved in the calcium signaling pathway, were enhanced by Zn2+ application. The disruption of plc-e abolished the cellulase-positive influence of Zn2+ in the early phase of induction, indicating that plc-e is involved in Zn2+-induced cellulase production. Furthermore, treatment with LaCl3 (a plasma membrane Ca2+ channel blocker) and deletion of crz1 (calcineurin-responsive zinc finger transcription factor 1) indicated that calcium signaling is partially involved in this process. Moreover, we identified the zinc-responsive transcription factor zafA, the transcriptional levels of which declined in response to Zn2+ stress. Deletion of zafA indicates that this factor plays a prominent role in mediating the Zn2+-induced excessive production of cellulase.

CONCLUSIONS

For the first time, we have demonstrated that Zn2+ is toxic to T. reesei, although promotes a marked increase in cellulase production. This positive influence of Zn2+ is facilitated by the plc-e gene and zafA transcription factor. These findings provide insights into the role of Zn2+ in T. reesei and the mechanisms underlying signal transduction in cellulase synthesis.

Multiple calcium signaling genes play a role in the circadian period of Neurospora crassa

The Ca2+ signaling genes cpe-1, plc-1, ncs-1, splA2, camk-1, camk-2, camk-3, camk-4, cmd, and cnb-1 are necessary for a normal circadian period length in Neurospora crassa. In addition, the Q10 values ranged between 0.8 and 1.2 for the single mutants lacking cpe-1, splA2, camk-1, camk-2, camk-3, camk-4, and cnb-1, suggesting that the circadian clock exhibits standard temperature compensation. However, the Q10 value for the ∆plc-1 mutant was 1.41 at 25 and 30 °C, 1.53 and 1.40 for the ∆ncs-1 mutant at 20 and 25 °C, and at 20 and 30 °C, respectively, suggesting a partial loss of temperature compensation in these two mutants. Moreover, expression of frq, a regulator of the circadian period, and the blue light receptor wc-1, were increased >2-fold in the Δplc-1, ∆plc-1; ∆cpe-1, and the ∆plc-1; ∆splA2 mutants at 20 °C. The frq mRNA level was increased >2-fold in the Δncs-1 mutant compared to the ras-1bd strain at 20 °C. Therefore, multiple Ca2+ signaling genes regulate the circadian period, by influencing expression of the frq and wc-1 genes that are critical for maintaining the normal circadian period length in N. crassa.

Speciation and spatial distribution of Eu(III) in fungal mycelium

Europium, as an easy-to-study analog of the trivalent actinides, is of particular importance for studying the behavior of lanthanides and actinides in the environment. Since different soil organisms can influence the migration behavior of these elements, a detailed knowledge of these interaction mechanisms is important. The aim of this study was to investigate the interaction of mycelia of selected wood-inhabiting (S. commune, P. ostreatus, L. tigrinus) and soil-inhabiting fungi (L. naucinus) with Eu(III). In addition to determining the Eu(III) complexes in the sorption solution, the formed Eu(III) fungal species were characterized using scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy, chemical microscopy in combination with the time-resolved laser-induced fluorescence spectroscopy. Our data show that S. commune exhibited significantly higher Eu(III) binding capacity in comparison to the other fungi. Depending on fungal strain, the metal was immobilized on the cell surface, in the cell membranes, and within the membranes of various organelles, or in the cytoplasm in some cases. During the bioassociation process two different Eu(III) fungal species were formed in all investigated fungal strain. The phosphate groups of organic ligands were identified as being important functional groups to bind Eu(III) and thus immobilize the metal in the fungal matrix. The information obtained contributes to a better understanding of the role of fungi in migration, removal or retention mechanisms of rare earth elements and trivalent actinides in the environment.

Enhancement of Fungal Enzyme Production by Radio-Frequency Electromagnetic Fields

Enzyme production by microorganisms on an industrial scale has demonstrated technical bottlenecks, such as low efficiency in enzyme expression and extracellular secretion. In this study, as a potential tool for overcoming these technical limits, radio-frequency electromagnetic field (RF-EMF) exposure was examined for its possibility to enhance production of an enzyme, α-amylase, in a filamentous fungus, Aspergillus oryzae. The RF-EMF perfectly resonated at 2 GHz with directivity radiation pattern and peak gain of 0.5 dB (0.01 Watt). Total protein concentration and activity of α-amylase measured in media were about 1.5-3-fold higher in the RF-EMF exposed (10 min) sample than control (no RF-EMF) during incubation (the highest increase after 16 h). The level of α-amylase mRNA in cells was approximately 2-8-fold increased 16 and 24 h after RF-EMF exposure for 10 min. An increase in vesicle accumulation within fungal hyphae and the transcription of some genes involved in protein cellular trafficking was observed in RF-EMF-exposed samples. Membrane potential was not changed, but the intracellular Ca2+ level was elevated after RF-EMF exposure. Our results suggest that RF-EMF can increase the extracellular level of fungal total proteins and α-amylase activity and the intracellular level of Ca2+.

Nanosheet-Facilitated Spray Delivery of dsRNAs Represents a Potential Tool to Control Rhizoctonia solani Infection

Rhizoctonia solani is one of the important pathogenic fungi causing several serious crop diseases, such as maize and rice sheath blight. Current methods used to control the disease mainly depend on spraying fungicides because there is no immunity or high resistance available in crops. Spraying double-strand RNA (dsRNA) for induced-gene silencing (SIGS) is a new potentially sustainable and environmentally friendly tool to control plant diseases. Here, we found that fluorescein-labelled EGFP-dsRNA could be absorbed by R. solani in co-incubation. Furthermore, three dsRNAs, each targeting one of pathogenicity-related genes, RsPG1, RsCATA, and RsCRZ1, significantly downregulated the transcript levels of the target genes after co-incubation, leading to a significant reduction in the pathogenicity of the fungus. Only the spray of RsCRZ1 dsRNA, but not RsPG1 or RsCATA dsRNA, affected fungal sclerotium formation. dsRNA stability on leaf surfaces and its efficiency in entering leaf cells were significantly improved when dsRNAs were loaded on layered double hydroxide (LDH) nanosheets. Notably, the RsCRZ1-dsRNA-LDH approach showed stronger and more lasting effects than using RsCRZ1-dsRNA alone in controlling pathogen development. Together, this study provides a new potential method to control crop diseases caused by R. solani.

Updating Insights into the Regulatory Mechanisms of Calcineurin-Activated Transcription Factor Crz1 in Pathogenic Fungi

Ca2+, as a second messenger in cells, enables organisms to adapt to different environmental stresses by rapidly sensing and responding to external stimuli. In recent years, the Ca2+ mediated calcium signaling pathway has been studied systematically in various mammals and fungi, indicating that the pathway is conserved among organisms. The pathway consists mainly of complex Ca2+ channel proteins, calcium pumps, Ca2+ transporters and many related proteins. Crz1, a transcription factor downstream of the calcium signaling pathway, participates in regulating cell survival, ion homeostasis, infection structure development, cell wall integrity and virulence. This review briefly summarizes the Ca2+ mediated calcium signaling pathway and regulatory roles in plant pathogenic fungi. Based on discussing the structure and localization of transcription factor Crz1, we focus on the regulatory role of Crz1 on growth and development, stress response, pathogenicity of pathogenic fungi and its regulatory mechanisms. Furthermore, we explore the cross-talk between Crz1 and other signaling pathways. Combined with the important role and pathogenic mechanism of Crz1 in fungi, the new strategies in which Crz1 may be used as a target to explore disease control in practice are also discussed.

Molecular Characterization of Phospholipase C in Infection Structure Differentiation Induced by Pear Fruit Surface Signals, Stress Responses, Secondary Metabolism, and Virulence of Alternaria alternata

Fungal pathogens use plant surface physiochemical signals to trigger specific developmental processes. To assess the role of phospholipase C (PLC) in mediating plant stimuli sensing of Alternaria alternata, the function of three PLC genes was characterized by constructing ΔAaPLC mutants. Here we showed that fruit wax-coated surfaces significantly induced appressorium formation in A. alternata and mutants. Germination of ΔAaPLC mutants did not differ from the wild type. Deletion of AaPLC1 led to the decrease of appressorium formation and infected hyphae, but the degree of reduction varies between the different types of waxes, with the strongest response to pear wax. Appressorium formation and infected hyphae of the ΔAaPLC1 mutant on dewaxed onion epidermis mounted with pear wax (θ4) were reduced by 14.5 and 65.7% after 8 h incubation, while ΔAaPLC2 and ΔAaPLC3 formed the same infection hyphae as wild type. In addition, AaPLC1 mutation caused pleiotropic effects on fungal biological function, including growth deficiency, changes in stress tolerance, weakening of pathogenicity to the host, as well as destruction of mycotoxin synthesis. Both AaPLC2 and AaPLC3 genes were found to have some effects on stress response and mycotoxin production. Taken together, AaPLC genes differentially regulate the growth, stress response, pathogenicity, and secondary metabolism of A. alternata.

Induction of cellulase production by Sr2+ in Trichoderma reesei via calcium signaling transduction

Trichoderma reesei RUT-C30 is a well-known high-yielding cellulase-producing fungal strain that converts lignocellulose into cellulosic sugar for resource regeneration. Calcium is a ubiquitous secondary messenger that regulates growth and cellulase production in T. reesei. We serendipitously found that adding Sr2+ to the medium significantly increased cellulase activity in the T. reesei RUT-C30 strain and upregulated the expression of cellulase-related genes. Further studies showed that Sr2+ supplementation increased the cytosolic calcium concentration and activated the calcium-responsive signal transduction pathway of Ca2+-calcineurin-responsive zinc finger transcription factor 1 (CRZ1). Using the plasma membrane Ca2+ channel blocker, LaCl3, we demonstrated that Sr2+ induces cellulase production via the calcium signaling pathway. Supplementation with the corresponding concentrations of Sr2+ also inhibited colony growth. Sr2+ supplementation led to an increase in intracellular reactive oxygen species (ROS) and upregulated the transcriptional levels of intracellular superoxide dismutase (sod1) and catalase (cat1). We further demonstrated that ROS content was detrimental to cellulase production, which was alleviated by the ROS scavenger N-acetyl cysteine (NAC). This study demonstrated for the first time that Sr2+ supplementation stimulates cellulase production and upregulates cellulase genes via the calcium signaling transduction pathway. Sr2+ leads to an increase in intracellular ROS, which is detrimental to cellulase production and can be alleviated by the ROS scavenger NAC. Our results provide insights into the mechanistic study of cellulase synthesis and the discovery of novel inducers of cellulase.

Exploring Relationships among Grapevine Chemical and Physiological Parameters and Leaf and Berry Mycobiome Composition

Improving our knowledge on biotic and abiotic factors that influence the composition of the grapevine mycobiome is of great agricultural significance, due to potential effects on plant health, productivity, and wine characteristics. Here, we assessed the influence of scion cultivar on the diversity and composition of fungal communities in the berries and leaves of three different cultivars. We generated DNA metabarcoding data, and statistically compared the richness, relative abundance, and composition of several functional groups of fungi among cultivars, which are partly explained by measured differences in chemical composition of leaves and berries and physiological traits of leaves. Fungal communities in leaves and berries show contrasting patterns among cultivars. The richness and relative abundance of fungal functional groups statistically differ among berry and leaf samples, but less so among cultivars. Community composition of the dominant functional groups of fungi, i.e., plant pathogens in leaves and saprotrophs in berries, differs significantly among cultivars. We also detect cultivar-level differences in the macro- and microelement content of the leaves, and in acidity and sugar concentration of berries. Our findings suggest that there appears to be a relatively diverse set of fungi that make up the grapevine mycobiome at the sampled terroir that spans several cultivars, and that both berry and leaf mycobiomes are likely influenced by the chemical characteristics of berries and leaves, e.g., pH and the availability of nutrients and simple carbohydrates. Finally, the correlation between fungal community composition and physiological variables in leaves is noteworthy, and merits further research to explore causality. Our findings offer novel insights into the microbial dynamics of grapevine considering plant chemistry and physiology, with implications for viticulture.

Heat shock proteins and the calcineurin-crz1 signaling regulate stress responses in fungi

The heat shock proteins (Hsps) act as a molecular chaperone to stabilize client proteins involved in various cell functions in fungi. Hsps are classified into different families such as HSP90, HSP70, HSP60, HSP40, and small HSPs (sHsps). Hsp90, a well-studied member of the Hsp family proteins, plays a role in growth, cell survival, and pathogenicity in fungi. Hsp70 and sHsps are involved in the development, tolerance to stress conditions, and drug resistance in fungi. Hsp60 is a mitochondrial chaperone, and Hsp40 regulates fungal ATPase machinery. In this review, we describe the cell functions, regulation, and the molecular link of the Hsps with the calcineurin-crz1 calcium signaling pathway for their role in cell survival, growth, virulence, and drug resistance in fungi and related organisms.

Physiological mechanisms by which gypsum increases the growth and yield of Lentinula edodes

Lentinula edodes is one of the most important commercially cultivated edible mushrooms. It is well known that gypsum (CaSO₄·2H₂O) supplementation in sawdust medium increases the yield of L. edodes, while the physiological mechanisms remain unclear. Our previous study showed that the acidification of the medium to pH 3.5-4.0 was essential for the growth of L. edodes. In this study, it was found that the oxalic acid excreted by L. edodes was responsible for the acidification of the medium. The biosynthesis of oxalic acid was regulated by the ambient pH and buffer capacity of the medium. To acidify the sawdust medium, the concentrations of total and soluble oxalate were 51.1 mmol/kg and 10.8 mmol/kg, respectively. However, when the concentration of soluble oxalate was 8.0 mmol/kg, the mycelial growth rate decreased by 29% compared with the control. Soluble oxalate was toxic to L. edodes, while soluble sulfate was nontoxic. CaSO₄ reacted with soluble oxalate to form nontoxic insoluble CaC₂O₄ and the strong acid H₂SO₄. When the CaSO₄ supplemented in sawdust medium was more than 25 mmol/kg, the soluble oxalate decreased to less than 1 mmol/kg, and the mycelial growth rate increased by 32% compared with the control. In conclusion, gypsum improved the growth and yield by relieving the toxicity of oxalate and facilitating the acidification of sawdust medium. KEY POINTS: • L. edodes excretes oxalic acid to acidify the ambient environment for growth. • Soluble oxalate is toxic to L. edodes. • Gypsum increases growth by reacting with oxalate to relieve its toxicity.

Effect of Zinc-Calcium on Xylose Consumption by Mucor circinelloides (MN128960): Xylitol and Ethanol Yield Optimization

Xylose is the second most abundant monomeric sugar on earth. Nevertheless, metabolizing xylose into ethanol is a complex process due to several biochemical reactions. Some microorganisms of the genus Mucor are suitable for this bioprocess. Using metal ions, such as zinc and calcium, allows some fungal species to increase their ethanol yield. In this work, the wild strain Mucor spp. (C1502) was molecularly identified via internal transcribed spacer (ITS) sequencing. Secondly, an optimization using response surface methodology (RSM) with a central composite experimental design (CCD) was carried out. The independent variables (X) were ZnSO4·7H2O (X1, 0.0–1.5 g/L) and CaCl2 (X2, 0.0–2.5 g/L) concentration in the fermentation broth in order to demonstrate the effect of these ions, xylose was used as the only carbon source. The dependent variables (Y) measured were ethanol yield (Y1, g ethanol/g xylose) and xylitol yield (Y2, g xylitol/g xylose). The identified strain, Mucor circinelloides, was given the accession number MN128960 by the NCBI. Once the optimal concentrations of zinc and calcium were calculated, experimental validation was performed, with the highest ethanol and xylitol yields reaching 0.36 g ethanol/g xylose and 0.35 g xylitol/g xylose, respectively. This study demonstrated that increasing the xylitol yield using the effect of the ions, zinc and calcium, increases the ethanol yield. Furthermore, M. circinelloides (C1502) can produce metabolites, such as ethanol and xylitol, from the xylose obtained from hemicellulose biomasses, which can be used as a carbon source at low cost and with great availability.

Calcium Affects Polyphosphate and Lipid Accumulation in Mucoromycota Fungi

Calcium controls important processes in fungal metabolism, such as hyphae growth, cell wall synthesis, and stress tolerance. Recently, it was reported that calcium affects polyphosphate and lipid accumulation in fungi. The purpose of this study was to assess the effect of calcium on the accumulation of lipids and polyphosphate for six oleaginous Mucoromycota fungi grown under different phosphorus/pH conditions. A Duetz microtiter plate system (Duetz MTPS) was used for the cultivation. The compositional profile of the microbial biomass was recorded using Fourier-transform infrared spectroscopy, the high throughput screening extension (FTIR-HTS). Lipid content and fatty acid profiles were determined using gas chromatography (GC). Cellular phosphorus was determined using assay-based UV-Vis spectroscopy, and accumulated phosphates were characterized using solid-state ³¹P nuclear magnetic resonance spectroscopy. Glucose consumption was estimated by FTIR-attenuated total reflection (FTIR-ATR). Overall, the data indicated that calcium availability enhances polyphosphate accumulation in Mucoromycota fungi, while calcium deficiency increases lipid production, especially under acidic conditions (pH 2-3) caused by the phosphorus limitation. In addition, it was observed that under acidic conditions, calcium deficiency leads to increase in carotenoid production. It can be concluded that calcium availability can be used as an optimization parameter in fungal fermentation processes to enhance the production of lipids or polyphosphates.