Colletotrichum trifolii TB3 kinase, a COT1 homolog, is light inducible and becomes localized in the nucleus during hyphal elongation

A Biological Comparison of Three Colletotrichum Species Associated with Alfalfa Anthracnose in Northern China

Anthracnose caused by various species of Colletotrichum is one of the most prevalent diseases in alfalfa worldwide that not only reduces forage yields but also severely compromises forage quality. A comprehensive survey was conducted in 2020 in the main production regions of northern China. The survey results showed that alfalfa anthracnose is prevalent in northern China, with the disease incidence ranging from 9% to 45% and the disease index from 5 to 17 (maximum possible score: 100). In total, 24 isolates were collected and identified as three Colletotrichum species (C. trifolii, C. truncatum and C. americae-borealis) based on morphological characteristics and phylogenetic analysis (combined sequences ITS, HIS3, ACT and GAPDH). The three species displayed remarkable environmental adaptability, exhibiting a capacity for growth, sporulation and conidial germination in temperatures ranging from 4 to 35 °C and in different nutrient conditions. Pathogenicity assays showed that C. trifolii was more virulent than the other two species, although the growth vigor (in terms of colony diameter, sporulation and conidial germination) of C. truncatum was the greatest.

Recent progress on harm, pathogen classification, control and pathogenic molecular mechanism of anthracnose of oil-tea

Oil tea (Camellia oleifera), mainly used to produce high-quality edible oil, is an important cash crop in China. Anthracnose of oil tea is a considerable factor that limits the yield of tea oil. In order to effectively control the anthracnose of oil tea, researchers have worked hard for many years, and great progress has been made in the research of oil tea anthracnose. For instance, researchers isolated a variety of Colletotrichum spp. from oil tea and found that Colletotrichum fructicola was the most popular pathogen in oil tea. At the same time, a variety of control methods have been explored, such as cultivating resistant varieties, pesticides, and biological control, etc. Furthermore, the research on the molecular pathogenesis of Colletotrichum spp. has also made good progress, such as the elaboration of the transcription factors and effector functions of Colletotrichum spp. The authors summarized the research status of the harm, pathogen types, control, and pathogenic molecular mechanism of oil tea anthracnose in order to provide theoretical support and new technical means for the green prevention and control of oil tea anthracnose.

The Complexity of Fungal Vision

Life, as we know it, would not be possible without light. Light is not only a primary source of energy, but also an important source of information for many organisms. To sense light, only a few photoreceptor systems have developed during evolution. They are all based on an organic molecule with conjugated double bonds that allows energy transfer from visible (or UV) light to its cognate protein to translate the primary physical photoresponse to cell-biological actions. The three main classes of receptors are flavin-based blue-light, retinal-based green-light (such as rhodopsin), and linear tetrapyrrole-based red-light sensors. Light not only controls the behavior of motile organisms, but is also important for many sessile microorganisms including fungi. In fungi, light controls developmental decisions and physiological adaptations as well as the circadian clock. Although all major classes of photoreceptors are found in fungi, a good level of understanding of the signaling processes at the molecular level is limited to some model fungi. However, current knowledge suggests a complex interplay between light perception systems, which goes far beyond the simple sensing of light and dark. In this article we focus on recent results in several fungi, which suggest a strong link between light-sensing and stress-activated mitogen-activated protein kinases.

A Dual-Color Imaging System for Sugarcane Smut Fungus Sporisorium scitamineum

The life cycle of the sugarcane smut fungus Sporisorium scitamineum is a multistep process. Haploid sporidia of compatible (MAT-1 versus MAT-2) mating types fuse to generate pathogenic dikaryotic hyphae to infect the host. Within the host tissues, diploid teliospores are formed and induce a characteristic sorus that looks like a black whip. The diploid teliospores germinate to form haploid sporidia by meiosis. In order to monitor fungal development throughout the whole life cycle, we expressed the green fluorescent protein (GFP) and red fluorescent protein (RFP) in S. scitamineum MAT-1 and MAT-2 sporidia, respectively. Observation by epifluorescence microscope showed that conjugation tube formation and sporidia fusion occurred at 4 to 8 h, and formation of dikaryotic filaments was detected at 12 h after mating. The resultant teliospores, with diffused GFP and RFP, underwent meiosis as demonstrated by septated hypha with single fluorescent signal. We demonstrated that GFP- and RFP-tagged strains can be used to study the life cycle development of the fungal pathogen S. scitamineum, including the sexual mating and meiosis events. This dual-color imaging system would be a valuable tool for investigation of biotic and abiotic factors that might affect the fungal life cycle development and pathogenesis.

Phenologic variation of major triterpenoids in regular and white Antrodia cinnamomea

BACKGROUND

Antrodia cinnamomea and its host Cinnamomum kanehirae are both endemic species unique to Taiwan. Many studies have confirmed that A. cinnamomea is rich in polysaccharides and triterpenoids that may carry medicinal effects in anti-cancer, anti-inflammation, anti-hypertension, and anti-oxidation. Therefore it is of interest to study the chemical variation of regular orange-red strains and white strains, which included naturally occurring and blue-light induced white A. cinnamomea.

RESULTS

The chemical profiles of A. cinnamomea extracts at different growth stages were compared using thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). The TLC and HPLC profiles indicated that specific triterpenoids varied between white and regular strains. Moreover, the compounds of blue-light induced white strain were similar to those of naturally occurring white strain but retained specific chemical characteristics in more polar region of the HPLC chromatogram of regular strain.

CONCLUSIONS

Blue-light radiation could change color of the regular A. cinnamomea from orange-red to white by changing its secondary metabolism and growth condition. Naturally occurring white strain did not show a significantly different composition of triterpenoid profiles up to eight weeks old when compared with the triterpenoid profiles of the regular strain at the same age. The ergostane-type triterpenoids were found existing in both young mycelia and old mycelia with fruiting body in artificial agar-plate medium culture, suggesting a more diversified biosynthetic pathway in artificial agar-plate culture rather than wild or submerged culture.

Restoration of female fertility in Trichoderma reesei QM6a provides the basis for inbreeding in this industrial cellulase producing fungus

BACKGROUND

Filamentous fungi are frequently used as production platforms in industrial biotechnology. Most of the strains involved were known as reproducing exclusively asexually thereby preventing the application of conventional strain breeding techniques. In the last decade, evidence was obtained that a number of these imperfect fungi possess a sexual life cycle, too. Trichoderma reesei, an industrial producer of enzymes for food, feed and biorefinery purposes, is heterothallic and takes a special position among industrially utilized species as all industrial strains are derived from the single MAT1-2 isolate QM6a. Consequently, strain improvement by crossing is not feasible within this strain line as this necessitates a MAT1-1 mating partner. Simply switching the mating type in one of the mating partners to MAT1-1, however, is not sufficient to produce a genotype capable of sexual reproduction with QM6a MAT1-2.

RESULTS

We have used a systems biology approach to identify genes restoring sexual reproduction in the QM6a strain line. To this end, T. reesei QM6a was crossed with the MAT1-1 wild-type strain CBS999.97. The descendants were backcrossed 8-times in two lineages with QM6a to obtain mating competent MAT1-1 strains with a minimal set of CBS999.97 specific genes. Comparative genome analysis identified a total of 73 genes of which two-encoding an unknown C2H2/ankyrin protein and a homolog of the WD-protein HAM5-were identified to be essential for fruiting body formation. The introduction of a functional ham5 allele in a mating type switched T. reesei QM6a allowed sexual crossing with the parental strain QM6a.

CONCLUSION

The finding that Trichoderma reesei is generally capable of undergoing sexual reproduction even under laboratory conditions raised hope for the applicability of classical breeding techniques with this fungus as known for plants and certain yeasts. The discovery that the wild-type isolate QM6a was female sterile, however, precluded any progress along that line. With the discovery of the genetic cause of female sterility and the creation of an engineered fertile strain we now provide the basis to establish sexual crossing in this fungus and herald a new era of strain improvement in T. reesei.

The N-terminal region of the Neurospora NDR kinase COT1 regulates morphology via its interactions with MOB2A/B

Nuclear Dbf2p-related (NDR) protein kinases are important for cell differentiation and polar morphogenesis in various organisms, yet some of their functions are still elusive. Dysfunction of the Neurospora crassa NDR kinase COT1 leads to cessation of tip extension and hyperbranching. NDR kinases require the physical interaction between the kinase's N-terminal region (NTR) and the MPS1-binding (MOB) proteins for their activity and functions. To study the interactions between COT1 and MOB2 proteins, we mutated several conserved residues and a novel phosphorylation site within the COT1 NTR. The phenotypes of these mutants suggest that the NTR is required for COT1 functions in regulating hyphal elongation and branching, asexual conidiation and germination. Interestingly, while both MOB2A and MOB2B promote proper hyphal growth, they have distinct COT1-dependent roles in regulation of macroconidiation. Immunoprecipitation experiments indicate physical association of COT1 with both MOB2A and MOB2B, simultaneously. Furthermore, the binding of the two MOB2 proteins to COT1 is mediated by different residues at the COT1 NTR, suggesting a hetero-trimer is formed. Thus, although MOB2A/B may have some overlapping functions in regulating hyphal tip extension, their function is not redundant and they are both required for proper fungal development.

Living colors in the gray mold pathogen Botrytis cinerea: codon-optimized genes encoding green fluorescent protein and mCherry, which exhibit bright fluorescence

The green fluorescent protein (GFP) and its variants have been widely used in modern biology as reporters that allow a variety of live-cell imaging techniques. So far, GFP has rarely been used in the gray mold fungus Botrytis cinerea because of low fluorescence intensity. The codon usage of B. cinerea genes strongly deviates from that of commonly used GFP-encoding genes and reveals a lower GC content than other fungi. In this study, we report the development and use of a codon-optimized version of the B. cinerea enhanced GFP (eGFP)-encoding gene (Bcgfp) for improved expression in B. cinerea. Both the codon optimization and, to a smaller extent, the insertion of an intron resulted in higher mRNA levels and increased fluorescence. Bcgfp was used for localization of nuclei in germinating spores and for visualizing host penetration. We further demonstrate the use of promoter-Bcgfp fusions for quantitative evaluation of various toxic compounds as inducers of the atrB gene encoding an ABC-type drug efflux transporter of B. cinerea. In addition, a codon-optimized mCherry-encoding gene was constructed which yielded bright red fluorescence in B. cinerea.

Molecular and morphological determination of Colletotrichum trifolii isolates originating from alfalfa

Colletotrichum trifolii is a fungal pathogen responsible for anthracnose disease in alfalfa. The isolates of C. trifolii were obtained from diseased alfalfa stems collected from field in Serbia. It was determined by pathogenicity examination that four isolates (Luc-7, Luc-17, Luc-27, Luc-33) can cause stem lesions on inoculated alfalfa plant. Our isolates were compared using reference isolates of C. trifolii (CBS 158.83). Isolates on MA and CDA developed olive green to grey colonies with white margin, while the substrate got dark olive green color. Conidiophores were hyaline, varied in length and produced a succession of conidia apically. Conidia were hyaline, straight, rounded at the ends, and non-septated with average size 7.85x3.87 ?m. Average sizes of appressoria were 7.5-16.5 x 5.5 x 8.9 ?m. The polymerase chain reaction (PCR) with one set of specific primers was used for the detection of examined isolates of Colletotrichum trifolii. Amplification of desired DNA fragment (590 bp) was determined using specific primer pair TB3-F/TB3-R. Achieved results of amplification indicated that the isolates Luc-7, Luc-17, Luc-27, as well as CBS 158.83, had traits of C. trifolli. Amplification and band on about 430 bp appeared in isolate Luc-33, which also belonged to C. trifolli species.

Photostimulation of Hypocrea atroviridis growth occurs due to a cross-talk of carbon metabolism, blue light receptors and response to oxidative stress

Light is a fundamental abiotic factor which stimulates growth and development of the majority of living organisms. In soil saprotrophic fungi, light is primarily known to influence morphogenesis, particularly sexual and asexual spore formation. Here we present a new function of light, the enhancement of mycelial growth. The photostimulated mycelial growth of the soil fungus Hypocrea atroviridis was detected on 17 (out of 95 tested carbon sources) carbohydrates and polyols, which are metabolically related to cellulose and hemicelluloses, and which are mainly available in the upper soil litter layer. This stimulation depends differently on the function of the two blue light receptor proteins BLR-1 and BLR-2, respectively, BLR-1 being responsible for carbon source selectivity and response to permanent light. Evocation of oxidative stress response in darkness imitates the photostimulation on nine of these carbon sources, and this effect was fully dependent on the function of BLR-1. We conclude that light in combination with the availability of litter-specific carbon sources serves as a signal for the fungus to be above ground, thereby stimulating fast growth in order to produce a maximum of propagules in the shortest time. We further deduce that this process involves oxidative stress response and the two blue light receptor proteins BLR-1 and BLR-2, the former playing the major role.

The STE20/germinal center kinase POD6 interacts with the NDR kinase COT1 and is involved in polar tip extension in Neurospora crassa

Members of the Ste20 and NDR protein kinase families are important for normal cell differentiation and morphogenesis in various organisms. We characterized POD6 (NCU02537.2), a novel member of the GCK family of Ste20 kinases that is essential for hyphal tip extension and coordinated branch formation in the filamentous fungus Neurospora crassa. pod-6 and the NDR kinase mutant cot-1 exhibit indistinguishable growth defects, characterized by cessation of cell elongation, hyperbranching, and altered cell-wall composition. We suggest that POD6 and COT1 act in the same genetic pathway, based on the fact that both pod-6 and cot-1 can be suppressed by 1) environmental stresses, 2) altering protein kinase A activity, and 3) common extragenic suppressors (ropy, as well as gul-1, which is characterized here as the ortholog of the budding and fission yeasts SSD1 and Sts5, respectively). Unlinked noncomplementation of cot-1/pod-6 alleles indicates a potential physical interaction between the two kinases, which is further supported by coimmunoprecipitation analyses, partial colocalization of both proteins in wild-type cells, and their common mislocalization in dynein/kinesin mutants. We conclude that POD6 acts together with COT1 and is essential for polar cell extension in a kinesin/dynein-dependent manner in N. crassa.

Depletion of Aspergillus nidulans cotA causes a severe polarity defect which is not suppressed by the nuclear migration mutation nudA2

The Aspergillus nidulans homologue of Neurospora crassa cot-1, cotA, encoding a member of the NDR protein kinase family, has been cloned and expressed under the control of the conditional alcA promoter. Depletion of CotA by repression of the alcA promoter led to a severe growth defect accompanied by loss of polarity. Germlings show greatly enlarged volume of the spores and hyphae, accompanied by an increase in number of nuclei per compartment, though the nucleus/volume ratio is not significantly altered. The depleted CotA phenotype was not suppressed by a nuclear migration mutation nudA2. Double mutants showed an additive, defective phenotype, unlike the suppression of the cot-1 ts mutation by ropy mutations seen in N. crassa, suggesting a different relationship between nuclear migration and the cot signalling pathway in A. nidulans. A functional CotA-GFP fusion protein was found in punctate regions of fluorescence similar to the distribution reported for human NDR2, and as a cap at the hyphal tip.

Cdc42 is required for proper growth and development in the fungal pathogen Colletotrichum trifolii

Cdc42 is a highly conserved small GTP-binding protein that is involved in regulating morphogenesis in eukaryotes. In this study, we isolated and characterized a highly conserved Cdc42 gene from Colletotrichum trifolii (CtCdc42), a fungal pathogen of alfalfa. CtCdc42 is, at least in part, functionally equivalent to Saccharomyces cerevisiae Cdc42p, since it restores the temperature-sensitive phenotype of a yeast Cdc42p mutant. Inhibition of CtCdc42 by expression of an antisense CtCdc42 or a dominant negative form of CtCdc42 (DN Cdc42) resulted in appressorium differentiation under noninductive conditions, suggesting that CtCdc42 negatively regulates pathogenic development in this fungus. We also examined the possible linkage between CtCdc42 and Ras signaling. Expression of a dominant active Cdc42 (DA Cdc42) in C. trifolii leads to aberrant hyphal growth under nutrient-limiting conditions. This phenotype was similar to that of our previously reported dominant active Ras (DA Ras) mutant. Also consistent with our observations of the DA Ras mutant, high levels of reactive oxygen species (ROS) were observed in the DA Cdc42 mutant, and proline restored the wild-type phenotype. Moreover, overexpression of DN Cdc42 resulted in a significant decrease in spore germination, virtually no hyphal branching, and earlier sporulation, again similar to what we observed in a dominant negative Ras (DN Ras) mutant strain. Interestingly, coexpression of DA Cdc42 with DN Ras resulted in germination rates close to wild-type levels, while coexpression of DN Cdc42 with the DA Ras mutant restored the wild-type phenotype. These data suggest that CtCdc42 is positioned as a downstream effector of CtRas to regulate spore germination and pathogenic development.

Identification and expression analysis of regulatory genes induced during conidiation in Exserohilum turcicum

Light influences numerous developmental and biochemical processes in fungi. The objectives of this research were to characterize the influence of light on growth and conidiation and associated gene expression in the plant pathogenic ascomycete, Exserohilum turcicum. We found that vegetative growth was more extensive in light/dark cycles than in constant light or darkness as measured by analysis of ergosterol content and genomic DNA. Cultures grown under continuous white light or blue light (approximately 465-480 nm) were developmentally arrested after the formation of conidiophores, whereas those grown in continuous darkness or a light/dark cycle produced mature conidia. Incubation of conidiophore-producing cultures in darkness for a minimum of 2 h was necessary and sufficient to initiate synchronous conidiation. To identify genes that are expressed during dark-induced conidiation, we constructed subtractive cDNA libraries from cultures grown under conidiation-permissive and -repressive conditions. From 816 sequenced EST clones in the conidiation-permissive and 310 in the repressive libraries, 12 putative regulatory genes were chosen for expression analysis by quantitative real-time PCR. The majority of those genes reached maximum expression by 2 h after initiation of the dark period and then declined to initial levels by 4-24 h in darkness. Expression of two dark-induced genes remained elevated after 24 h in darkness but was reset to initial levels if cultures were returned to light. This study revealed several genes whose expression increased rapidly after dark induction of conidiation, suggesting that they encode regulators of asexual development in E. turcicum.

The COT1 homologue CPCOT1 regulates polar growth and branching and is essential for pathogenicity in Claviceps purpurea

Claviceps purpurea, the ergot fungus, is a common grass pathogen attacking exclusively young ovaries. Its pathogenic development involves an early phase of directed growth (with strictly suppressed branching) towards the floral vascular tissue. Since Ser/Thr protein kinases of the NDR family have been shown to be involved in polar growth and branching in fungi, we have analyzed a C. purpurea homologue of the Neurospora crassa cot-1 gene, cpcot1. It encodes a functional homologue of COT1 since it can fully complement the N. crassa cot-1 mutant phenotype. Delta cpcot1 mutants are significantly impaired in vegetative growth properties: they are characterized by hyperbranching, reduced growth rate, and decreased conidiation. Infection studies on rye plants and isolated ovaries show that the delta cpcot1 mutants are apathogenic; microscopical analyses indicate a very early block, probably in penetration. Thus CPCOT1 is not only involved in polarity and branching and hence oriented growth in the host tissue as expected, but it is essential for the initiation of infection.

Photomorphogenesis in the hypogeous fungus Tuber borchii: isolation and characterization of Tbwc-1, the homologue of the blue-light photoreceptor of Neurospora crassa

Truffles form a group of plant-symbiotic Ascomycetes whose hypogeous life cycle is poorly understood. Here we present initial evidence for the influence of light on Tuber borchii mycelial growth and the identification and cloning of a gene, Tbwc-1, homologous to a blue-light photoreceptor of Neurospora crassa. Blue-light irradiation of T. borchii colonies inhibits their apical growth. It also alters apical growth in N. crassa. In Neurospora, the response is controlled by a nuclear photoreceptor, NcWC-1 (White Collar-1), which consists of a sensor domain (LOV) and a transcriptional factor moiety. We isolated a gene (Tbwc-1) whose deduced amino acid sequence shows a high similarity and colinearity of domains with NcWC-1, except for the polyglutamine regions. As previously found in Neurospora, Tbwc-1 mRNA is under light control and its steady state level increases upon irradiation. In silico analysis of the TbWC-1 sensor domain (LOV) supports the hypothesis that TbWC-1 is a photoreceptor, while the absence of the two polyglutamine regions involved in transcriptional activation in Neurospora suggests that this function in Tuber could be lost.

Deletion of a hypoviral-regulated cppk1 gene in a chestnut blight fungus, Cryphonectria parasitica, results in microcolonies

The cppk1 gene encodes a Ser/Thr protein kinase of Cryphonectria parasitica and is transcriptionally up-regulated by the presence of hypovirus CHV1-EP713. A cppk1-null mutant was constructed to determine the function of cppk1. The cppk1-null mutant was initially isolated as a heterokaryotic form containing both wild-type and cppk1-deleted nuclei. The pure cppk1-null homokaryon was obtained by the single spore isolation of the heterokaryon. While the parental heterokaryon appeared normal, the pure cppk1-null mutant exhibited dramatic changes in colony morphology. It showed characteristics of microcolonial growth. The functional complementation, restoration of filamentous growth, of the cppk1-null mutant using a wild-type cppk1 gene indicated that the phenotypic changes were due to the disruption of cppk1. Neither sporulation nor hyphal differentiation into feeding hyphae, a mycelial mat, or aerial hyphae was observed in the cppk1-null mutant. Instead of bright yellow, dark brown pigmentation appeared as the culture grew. Hyphae were shortened and hyperbranched with globose to bulbose cells. Electron microscopy revealed the presence of intrahyphal hyphae, the most striking ultrastructural change. Subtle changes in the expression of CpPK1 resulted in abnormalities in colony morphology and pigmentation, which indicated that cppk1 is important for coordinating growth with development and maintaining cell wall integrity.

Dominant active Rac and dominant negative Rac revert the dominant active Ras phenotype in Colletotrichum trifolii by distinct signalling pathways

The small G-protein superfamily is an evolutionarily conserved group of GTPases that regulate diverse signalling pathways including pathways for growth and development in eukaryotes. Previously, we showed that dominant active mutation in the unique Ras gene (DARas) of the fungal phytopathogen Colletotrichum trifolii displays a nutrient-dependent phenotype affecting polarity, growth and differentiation. Signalling via the MAP kinase pathway is significantly impaired in this mutant as well. Here we describe the cloning and functional characterization of Rac (Ct-Rac1), a member of the Rho family of G proteins. Ct-Rac1 expression is downregulated by DARas under limiting nutrition. Co-expression of DARas with dominant active Rac (DARac) stimulates MAPK activation and restores the wild-type phenotype. Inhibition of MAPK activation suppresses phenotypic restoration suggesting Rac-mediated MAPK activation is responsible for reversion to the wild-type phenotype. We also examined the role of reactive oxygen species (ROS) in these genetic backgrounds. The DARas mutant strain generates high levels of ROS as determined by DCFH-DA fluorescence. Co-expression with DNRac decreases ROS generation to wild-type levels and restores normal fungal growth and development. Pretreatment of DARas with antioxidants or a cytosolic phospholipase A2 inhibitor also restores the wild-type phenotype. These findings suggest that Ras-mediated ROS generation is dependent on a Rac-cPLA(2)-linked signalling pathway. Taken together, this study provides evidence that Rac functions to restore the hyphal morphology of DARas by regulating MAPK activation and intracellular ROS generation.