Conidial Development Research Articles

WetA bridges cellular and chemical development in Aspergillus flavus.

Bridging cellular reproduction and survival is essential for all life forms. Aspergillus fungi primarily reproduce by forming asexual spores called conidia, whose formation and maturation is governed by the central genetic regulatory circuit BrlA→AbaA→WetA. Here, we report that WetA is a multi-functional regulator that couples spore differentiation and survival, and governs proper chemical development in Aspergillus flavus. The deletion of wetA results in the formation of conidia with defective cell walls and no intra-cellular trehalose, leading to reduced stress tolerance, a rapid loss of viability, and disintegration of spores. WetA is also required for normal vegetative growth, hyphal branching, and production of aflatoxins. Targeted and genome-wide expression analyses reveal that WetA exerts feedback control of brlA and that 5,700 genes show altered mRNA levels in the mutant conidia. Functional category analyses of differentially expressed genes in ΔwetA RNA-seq data indicate that WetA contributes to spore integrity and maturity by properly regulating the metabolic pathways of trehalose, chitin, α-(1,3)-glucan, β-(1,3)-glucan, melanin, hydrophobins, and secondary metabolism more generally. Moreover, 160 genes predicted to encode transcription factors are differentially expressed by the absence of wetA, suggesting that WetA may play a global regulatory role in conidial development. Collectively, we present a comprehensive model for developmental control that bridges spore differentiation and survival in A. flavus.

Construction of Setosphaeria turcica STK1-EGFP fusion gene vector and its expression in Pichia pastoris

STK1 is one important MAPK gene regulating the conidial development, osmotic stress and pathogenicity of Setosphaeria turcica. At first, the Pichia pastoris GS115 expression vector pPIC3.5K-EGFP containing enhanced green fluorescent protein gene (EGFP) was constructed, then STK1 gene was first amplified by PCR with the template of cDNA of S. turcica model isolate 01-23, and then cloned into the vector pPIC3.5K-EGFP with enhanced green fluorescent protein gene (EGFP) to construct the STK1-EGFP fusion gene expression vector pPIC3.5K-STK1-EGFP. The vector was transformed into the susceptible cells of Pichia pastoris GS115 by electric shock process, and the transformants were identified by MD medium screening and PCR determination. The STK1 gene and EGFP gene could be expressed effectively and stably in the transformants as detected by RT-PCR and fluorescence observation. In addition, we also found that the Kozak sequence before the start codon of STK1 gene could increase 4.8 folds expression level of STK1- EGFP fusion gene. The above research results laid a good foundation for subcellular localization and antibody preparation of STK1 protein.

A cryptic pigment biosynthetic pathway uncovered by heterologous expression is essential for conidial development in Pestalotiopsis fici.

Spore pigmentation is very common in the fungal kingdom. The best studied pigment in fungi is melanin which coats the surface of single cell spores. What and how pigments function in a fungal species with multiple cell conidia is poorly understood. Here, we identified and deleted a polyketide synthase (PKS) gene PfmaE and showed that it is essential for multicellular conidial pigmentation and development in a plant endophytic fungus, Pestalotiopsis fici. To further characterize the melanin pathway, we utilized an advanced Aspergillus nidulans heterologous system for the expression of the PKS PfmaE and the Pfma gene cluster. By structural elucidation of the pathway metabolite scytalone in A. nidulans, we provided chemical evidence that the Pfma cluster synthesizes DHN melanin. Combining genetic deletion and combinatorial gene expression of Pfma cluster genes, we determined that the putative reductase PfmaG and the PKS are sufficient for the synthesis of scytalone. Feeding scytalone back to the P. fici ΔPfmaE mutant restored pigmentation and multicellular adherence of the conidia. These results cement a growing understanding that pigments are essential not simply for protection of spores from biotic and abiotic stresses but also for spore structural development.

COP9 signalosome subunit PfCsnE regulates secondary metabolism and conidial formation in Pestalotiopsis fici.

The COP9 signalosome (CSN) is a highly conserved multiprotein complex in all eukaryotes and involved in regulation of organism development. In filamentous fungi, several lines of evidence indicate that fungal development and secondary metabolism (SM) are mediated by the fifth subunit of CSN, called CsnE. Here we uncover a connection with CsnE and conidial formation as well as SM regulation in the plant endophytic fungus Pestalotiopsis fici. A homology search of the P. fici genome with CsnE, involved in sexual development and SM in Aspergillus nidulans, identified PfCsnE. Deletion of PfcsnE resulted in a mutant that stopped conidial production, but the conidia are recovered in a PfcsnE complemented strain. This indicates that PfCsnE is required for the formation of conidia. Secondary metabolite analysis demonstrated that the ΔPfcsnE strain produced more chloroisosulochrin, less ficiolide A production in comparison to wild type (WT). Transcriptome analysis of WT and ΔPfcsnE strains indicated that PfcsnE impacts the expression levels of 8.37% of 14,797 annotated genes. Specifically, nine biosynthetic gene clusters (BGCs) were up-regulated and three BGCs were down-regulated by PfCsnE. Our results suggest that PfCsnE plays major roles in SM regulation and conidial development in P. fici.

A class-II myosin is required for growth, conidiation, cell wall integrity and pathogenicity of Magnaporthe oryzae

ABSTRACTIn eukaryotic organisms, myosin proteins are the major ring components that are involved in cytokinesis. To date, little is known about the biologic functions of myosin proteins in Magnaporthe oryzae. In this study, insertional mutagenesis conducted in M. oryzae led to identification of Momyo2, a pathogenicity gene predicted to encode a class-II myosin protein homologous to Saccharomyces cerevisiae Myo1. According to qRT-PCR, Momyo2 is highly expressed during early infectious stage. When this gene was disrupted, the resultant mutant isolates were attenuated in virulence on rice and barley. These were likely caused by defective mycelial growth and frequent emergence of branch hyphae and septum. The Momyo2 mutants were also defective in conidial and appressorial development, characterized by abnormal conidia and appressoria. These consequently resulted in plant tissue penetration defects that the wild type strain lacked, and mutants being less pathogenic. Cytorrhysis assay, CFW staining of appressorium and monitoring of protoplast release suggested that appressorial wall was altered, presumably affecting the level of turgor pressure within appressorium. Furthermore, impairments in conidial germination, glycogen metabolites, tolerance to exogenous stresses and scavenging of host-derived reactive oxygen species were associated with defects on appressorium mediated penetration, and therefore attenuated the virulence of Momyo2 mutants. Taken together, these results suggest that Momyo2 plays pleiotropic roles in fungal development, and is required for the full pathogenicity of M. oryzae.

NapA Mediates a Redox Regulation of the Antioxidant Response, Carbon Utilization and Development in Aspergillus nidulans.

The redox-regulated transcription factors (TFs) of the bZIP AP1 family, such as yeast Yap1 and fission yeast Pap1, are activated by peroxiredoxin proteins (Prxs) to regulate the antioxidant response. Previously, Aspergillus nidulans mutants lacking the Yap1 ortholog NapA have been characterized as sensitive to H2O2 and menadione. Here we study NapA roles in relation to TFs SrrA and AtfA, also involved in oxidant detoxification, showing that these TFs play different roles in oxidative stress resistance, catalase gene regulation and development, during A. nidulans life cycle. We also uncover novel NapA roles in repression of sexual development, normal conidiation, conidial mRNA accumulation, and carbon utilization. The phenotypic characterization of ΔgpxA, ΔtpxA, and ΔtpxB single, double and triple peroxiredoxin mutants in wild type or ΔnapA backgrounds shows that none of these Prxs is required for NapA function in H2O2 and menadione resistance. However, these Prxs participate in a minor NapA-independent H2O2 resistance pathway and NapA and TpxA appear to regulate conidiation along the same route. Using transcriptomic analysis we show that during conidial development NapA-dependent gene expression pattern is different from canonical oxidative stress patterns. In the course of conidiation, NapA is required for regulation of at least 214 genes, including ethanol utilization genes alcR, alcA and aldA, and large sets of genes encoding proteins involved in transcriptional regulation, drug detoxification, carbohydrate utilization and secondary metabolism, comprising multiple oxidoreductases, membrane transporters and hydrolases. In agreement with this, ΔnapA mutants fail to grow or grow very poorly in ethanol, arabinose or fructose as sole carbon sources. Moreover, we show that NapA nuclear localization is induced not only by oxidative stress but also by growth in ethanol and by carbon starvation. Together with our previous work, these results show that SakA-AtfA, SrrA and NapA oxidative stress-sensing pathways regulate essential aspects of spore physiology (i.e., cell cycle arrest, dormancy, drug production and detoxification, and carbohydrate utilization).

Anthocyanins from Clitoria ternatea Attenuate Food-Borne Penicillium expansum and its Potential Application as Food Biopreservative

Clitoria ternatea or Commonly known blue pea, is a perennial climber crop native to Asian countries. The current study was aimed to evaluate the antimicrobial activity C. ternatea extract on food borne microorganisms and its antifungal effect on Penicillium expansum. The extract showed significant antimicrobial activity against 3 Gram positive bacteria, 2 Gram negative bacteria and 1 filamentous fungus on disc diffusion assay. The extract also showed good biocidal effect on all Gram positive bacteria tested and P. expansum. However, the kill curve analysis revealed that the fungicidal activity of the extract against P. expansum conidia was depend on the concentration of the extract and the time of exposure of the conidia to the extract. The scanning electron micrograph of the extract treated P. expansum culture showed alterations in the morphology of fungal hyphae. The germination of P. expansum conidia was completely inhibited and conidial development was totally suppressed by the extract, suggesting the possible mode of action of anthocyanin. Besides, the extract also exhibited 5.0-log suppression of microbial growth relative to control in the rice model. The results indicate the potential use of the C. ternatea anthocyanin as food biopreservative.

Role of the Talaromyces marneffei (Penicillium marneffei) sakA gene in nitrosative stress response, conidiation and red pigment production.

Stress-activated MAPK pathways are systems used to regulate the stress adaptation of most fungi. It has been shown that in Talaromyces marneffei (Penicillium marneffei), a pathogenic dimorphic fungus, the sakA gene is involved, not only in tolerance against oxidative and heat stresses, but also in playing a role in asexual development, yeast cell generation in vitro and survival inside macrophage cell lines. In this study, the role of the T. marneffei sakA gene on the nitrosative stress response and the regulation of gene expression were investigated. The susceptibility of the sakA mutant to NaNO2 was investigated using drop dilution assay and the expression of genes of interest were determined by RT-PCR, comparing them to the wild-type and complemented strains. The results demonstrated that the T. marneffei sakA gene played a role in the stress response to NaNO2, the expression of genes functioning in conidial development (brlA, abaA and wetA) and red pigment biosynthesis (pks3, rp1, rp2 and rp3). These findings suggest that T. marneffei sakA is broadly involved in a wide variety of cell activities, including stress response, cell morphogenesis, asexual development and pigmentation.

MAP kinase gene STK1 is required for hyphal, conidial, and appressorial development, toxin biosynthesis, pathogenicity, and hypertonic stress response in the plant pathogenic fungus Setosphaeria turcica

The mitogen-activated protein kinase (MAPK), a key signal transduction component in the MAPK cascade pathway, regulates a variety of physiological activities in eukaryotes. However, little is known of the role MAPK plays in phytopathogenic fungi. In this research, we cloned the MAPK gene STK1 from the northern corn leaf blight pathogen Setosphaeria turcica and found that the gene shared high homology with the high osmolality glycerol (HOG) MAPK gene HOG1 of Saccharomyces cerevisiae. In addition, gene knockout technology was employed to investigate the function of STK1. Gene knockout mutants (KOs) were found to have altered hyphae morphology and no conidiogenesis, though they did show similar radial growth rate compared to the wild-type strain (WT). Furthermore, microscope observations indicated that STK1 KOs did not form normal appressoria at 48 h post-inoculation on a hydrophobic surface. STK1 KOs had reduced virulence, a significantly altered Helminthosporium turcicum (HT)-toxin composition, and diminished pathogenicity on the leaves of susceptible inbred corn OH43. Mycelium morphology appeared to be significantly swollen and the radial growth rates of STK1 KOs declined in comparison with WT under high osmotic stress. These results suggested that STK1 affects the hyphae development, conidiogenesis, and pathogenicity of S. turcica by regulating appressorium development and HT-toxin biosynthesis. Moreover, the gene appears to be involved in the hypertonic stress response in S. turcica.

Fungi associated with hibernating bats in New Brunswick caves: the genus Leuconeurospora

Two species of Leuconeurospora, Leuconeurospora capsici (J.F.H. Beyma) Malloch, Sigler & Hambleton and Leuconeurospora polypaeciloides Malloch, Sigler & Hambleton (Ascomycota: Pseudeurotiaceae), are reported from the fur and skin of hibernating bats and from other substrata in caves in New Brunswick, Canada. Separate analyses using ITS, RPB1, and RPB2 DNA sequence data are in agreement and show these two species and the type species, Leuconeurospora pulcherrima (G. Winter) Malloch & Cain, form discrete clades within a distinct Leuconeurospora clade. The three species are distinguishable morphologically by their anamorphs, having dark conidia in L. capsici, hyaline conidia in L. polypaeciloides, and no conidia in L. pulcherrima. Ascomata and ascospores are produced in L. pulcherrima and in mated isolates of L. polypaeciloides, but have not been observed in L. capsici. Leuconeurospora species are psychrotolerant, with faster growth and heavier conidial development at 7 °C than at 22 °C. Of 151 bats sampled from 10 caves, 51 yielded isolates of L. polypaeciloides and 15 yielded L. capsici. The results were not uniform: neither species was isolated from bats in three caves, while three caves yielded isolates of both species and two yielded L. polypaeciloides only. These species were also isolated from cave walls and arthropods in the cave.

Azoxystrobin and propiconazole offer significant potential for rice blast (Pyricularia oryzae) management in Australia

Fungicides are the preferred rice blast (Pyricularia oryzae) control option by farmers. However, no fungicides are yet registered for this purpose in Australia. Hence, it is important to test the baseline sensitivity of P. oryzae isolates collected from blast-affected regions across northern Australia, which have not yet been exposed to the fungicides, as part of a resistance management strategy. Further, it is also important to investigate and compare effect of application timing of fungicides on conidial development, including germination and germ tube growth, and penetration on susceptible rice. The EC50 of a collection of fungicide-sensitive blast isolates were within the range of 0.02–2.02 and 0.06–1.91 mg L−1 for azoxystrobin and propiconazole, respectively. Azoxystrobin was shown to have greater inhibitory effect on conidial germination than propiconazole. In addition, for pre-inoculation application, only germ tubes in the presence of external nutrients continued to grow from 24 to 48 hpi. On susceptible seedlings, both fungicides completely controlled blast disease when applied the same day as inoculation. However, for pre- or post-inoculation application of fungicide, the extent of disease control was reduced, with azoxystrobin more efficacious than propiconazole. A stimulatory effect of both fungicides at low dose was observed on certain P. oryzae isolates. This is the first study to assess the baseline sensitivity of the P. oryzae population in Australia and the first to report a stimulatory effect of low azoxystrobin concentration on growth of P. oryzae. The study highlights, for the first time, the critical role of external nutrients in promoting germ tube growth under fungicide stress conditions. Lastly, it demonstrates the high degree of efficacy of the fungicides and their potential for future rice blast management in Australia.

The cellular proteome is affected by a gelsolin (BbGEL1) during morphological transitions in aerobic surface versus liquid growth in the entomopathogenic fungus Beauveria bassiana.

The gelsolin superfamily includes seven protein members: gelsolin, villin, adseverin, CapG, advillin, supervillin and flightless I. The gelsolin proteins are actin-binding proteins that contain three or six gelsolin-like domains, and they play important roles in remodelling actin dynamics and cellular processes in eukaryotes. The entomopathogenic fungus Beauveria bassiana expresses a unique CapG protein (BbGEL1) that contains three gelsolin-like domains. BbGEL1p is associated with actin during mycelial growth and plays an important role in fungal morphological transitions under both aerobic and submerged conditions. The ΔBbGEL1 mutant displays abnormal spore-producing structures that reduce the conidial and blastospore yields by approximately 70% and 90% respectively. The virulence of the ΔBbGEL1 mutant is notably reduced as indicated by topical and intrahemocoel injection assays. Two comparative proteomics analyses indicated that BbGEL1 has significantly different roles in the development of conidia and blastospores, and the results revealed the potential targets of BbGEL1 in the corresponding developmental processes. Additionally, as an overlapping downstream protein of BbGEL1, the hydrophobin-like protein gene BbHyd3 is required for conidiation but has a negative role in blastospore formation. Our findings indicate that in addition to its function as an actin-interacting protein, BbGEL1 contributes to fungal morphological transitions via broad genetic pathways.

Conserved and divergent roles of the HOG1 kinase of Alternaria longipes in mycelial and conidial development, multi-stress responses, melanin production and pathogenicity

The protein kinase HOG1 in high osmolarity glycerol pathway is one of mitogen-activated protein kinases and plays an important role in fungi cellular responses to external stress and stimuli. In this study, AlHOG1, a yeast HOG1 homolog, was isolated from tobacco pathogenic fungus Alternaria longipes and its disrupted mutants were generated using homologous recombination. Compared with the wild-type strain, the mutants grew slower under Minimal-Media, produced less conidia on Potato-Dextrose-Agar and showed a retardation phenotype in conidial germination rate. Colony color observation indicated that AlHOG1 most likely negatively regulated melanin production under nutrients-deficient or osmotic stress. The same action mode of AlHOG1 on hyphal growth in response to certain carbon or nitrogen sources was speculated. Additionally, the disrupted strains were sensitive to osmotic and oxidative stress, and showed increased resistance to dicarboximide, phenylpyrrole and carbendazim fungicides. Meanwhile, results from the comparative analysis between the AlHOG1- and the AlHK1 (encoding a group III histidine kinase)-disrupted mutants showed that AlHOG1 mediated-pathway was partly regulated by the upstream AlHK1 kinase for cellular resistance to salts osmotic stress and that AlHK1 was a primary regulator for cellular sugar and fungicides stress adaptation and likely modulated both AlHOG1-mediated pathway and other unknown mechanisms. Noteworthily, AlHOG1 but not AlHK1 was confirmed to be associated with high concentration glycerol adaptation, which is the first report to our knowledge. Overall, our results indicated that AlHOG1 was involved in multiple physiological processes in A. longipes, including mycelial and conidial development, melanin production, nutrients sensing and multi-stress responses.

Identification and functional analysis of endogenous nitric oxide in a filamentous fungus

In spite of its prevalence in animals and plants, endogenous nitric oxide (NO) has been rarely reported in fungi. We present here our observations on production of intracellular NO and its possible roles during development of Neurospora crassa, a model filamentous fungus. Intracellular NO was detected in hypha 8–16 hours after incubation in Vogel’s minimal liquid media and conidiophores during conidiation using a fluorescent indicator (DAF-FM diacetate). Treatment with cPTIO, an NO scavenger, significantly reduced fluorescence levels and hindered hyphal growth in liquid media and conidiation, whereas exogenous NO enhanced hyphal extension on VM agar media and conidia formation. NO scavenging also dramatically diminished transcription of con-10 and con-13, genes preferentially expressed during conidiation. Our results suggest that intracellular NO is generated in young hypha growing in submerged culture and during conidia development and regulate mycelial development and conidia formation.

The causal agent of citrus postbloom fruit drop, Colletotrichum acutatum, can survive on weeds

Postbloom fruit drop is an important citrus disease caused by Colletotrichum acutatum. Severe outbreaks can develop when rainy periods occur during citrus bloom. Under these conditions, explosive epidemics are observed despite relatively short inoculum dispersal distances typical of this pathogen. C. acutatum can survive on citrus leaf surfaces after formation of appressoria, but survival on weeds has not been characterized. The survival of C. acutatum on seven species of weeds was evaluated under greenhouse conditions by artificial inoculation and subsequent recovery of the pathogen in-vitro. Conidial germination and appressorial development of C. acutatum were observed on the surface of all inoculated leaves. The pathogen was recovered from weed leaves at 30, 60 and 90 days after inoculation. Statistically, there was no difference in survival of C. acutatum among sample times post-inoculation. Although survival varied on different weed species, no symptoms were observed on inoculated leaves. All citrus flowers inoculated with isolates recovered from inoculated weeds showed typical symptoms of postbloom fruit drop. We conclude that the weed species tested may serve as potential alternative hosts for C. acutatum.

Early Development of Powdery Mildew on Cucumber Leaves Acclimatized to Illumination with Different Red-to-far-red Ratios

The development of powdery mildew fungus (Podosphaera xanthii) is suppressed on cucumber (Cucumis sativus L.) seedlings acclimatized to higher red-to-far-red ratio (R:FR) than natural R:FR (≈1.2), but its early development and any limiting factors are still unclear. The present study evaluated conidial germination, initial invasion, and subsequent development of P. xanthii on cucumber seedlings raised under light-emitting diode (LED) lights with R:FRs of 1.2, 5.0, or 10. There were no differences in conidial germination or initial invasion between the treatments, so there was no effect of acclimatization to R:FR on either. But, the development of hyphae, hyphal cells, and haustoria after inoculation were suppressed on seedlings acclimatized to higher R:FR. Because differences occurred only after the initial invasion, nonstructural properties of the host leaves may have affected conidial development. Higher R:FR also suppressed conidial development under natural light filtered through a photo-selective film, which absorbs near-infrared (NIR)-light. However, this effect was reduced when the plants were moved to natural R:FR after inoculation, possibly because of reacclimatization of the seedlings.

Transmission electron microscopy of Tuberculina species (Helicobasidiales) reveals an unique mode of conidiogenesis within Basidiomycota

Tuberculina species represent the asexual life stage of the plant-parasitic sexual genus Helicobasidium. Tuberculina species are distributed all over the world, living in antagonistic symbiosis with over 150 rust species from at least 15 genera. Within the Basidiomycota, besides the spermogonia of rust fungi, only Tuberculina species develop distinct fructifications in the haplophase. However, the knowledge of conidiogenesis in Tuberculina is meagre. Therefore, conidial development in Tuberculina maxima, Tuberculina persicina, and Tuberculina sbrozzii was studied using transmission electron microscopy, and compared to each other as well as to spermatia formation in rust fungi. Significant ultrastructural characteristics such as the movement of nuclei in the process of conidium formation, and formation of the initial and late stages of conidiogenesis are documented. The mode of conidiogenesis of Tuberculina species is unique within the Basidiomycota in that (1) it is realized by haploid fructifications, (2) it is holoblastic, without annellidic proliferation, (3) the nucleus of the conidiogenous cell moves towards the forming conidium, divides, and no daughter nucleus remains inside the conidiogenous cell, and (4) the conidiogenous cell retains only cytoplasmic residues after the development of a single conidium, and a successive conidium is not produced.

The C2H2-type transcription factor, FlbC, is involved in the transcriptional regulation of Aspergillus oryzae glucoamylase and protease genes specifically expressed in solid-state culture.

Aspergillus oryzae produces a large amount of secreted proteins in solid-state culture, and some proteins such as glucoamylase (GlaB) and acid protease (PepA) are specifically produced in solid-state culture, but rarely in submerged culture. From the disruption mutant library of A. oryzae transcriptional regulators, we successfully identified a disruption mutant showing an extremely low production level of GlaB but a normal level of α-amylase production. This strain was a disruption mutant of the C2H2-type transcription factor, FlbC, which is reported to be involved in the regulation of conidiospore development. Disruption mutants of other upstream regulators comprising a conidiation regulatory network had no apparent effect on GlaB production in solid-state culture. In addition to GlaB, the production of acid protease in solid-state culture was also markedly decreased by flbC disruption. Northern blot analyses revealed that transcripts of glaB and pepA were significantly decreased in the flbC disruption strain. These results suggested that FlbC is involved in the transcriptional regulation of genes specifically expressed under solid-state cultivation conditions, possibly independent of the conidiation regulatory network.

Studies in genera similar to Torula: Bahusaganda, Bahusandhika, Pseudotorula, and Simmonsiella gen. nov.

A generic key is presented to delimit Torula from seven hyphomycete genera whose type species were at one time included in the genus or whose conidium ontogeny and conidium development appear similar or superficially similar to that of Torula herbarum, the type of the genus. In Bahusaganda, two new species are described (B. elliseverhartii and B. simmonsii spp. nov.) and three new combinations made (B. ambrosiae, B. elaeodes, and B. heteromorpha combs. nov.). In Bahusandhika, one new species (B. hughesii sp. nov.) is introduced, and two new combinations made (B. rhombica and B. terrestris combs. nov.), along with emendations in the circumscription of B. caligans and B. intercalaris. Latorua is considered synonymous with Bahusandhika. In Pseudotorula, one new combination is made (P. sundara comb. nov.), and one emendation proposed (P. helica). The transfer of Dwayabeeja sundara, the type species of the genus, to Pseudotorula will require a new generic name to be introduced for D. aethiopica and D. cubensis. The new generic name Simmonsiella is established for Torula ndjilensis. Bahusandhika compacta is shown to be synonymous with Torula verrucospora.

Functional Genomic Analysis of Aspergillus flavus Interacting with Resistant and Susceptible Peanut.

In the Aspergillus flavus (A. flavus)–peanut pathosystem, development and metabolism of the fungus directly influence aflatoxin contamination. To comprehensively understand the molecular mechanism of A. flavus interaction with peanut, RNA-seq was used for global transcriptome profiling of A. flavus during interaction with resistant and susceptible peanut genotypes. In total, 67.46 Gb of high-quality bases were generated for A. flavus-resistant (af_R) and -susceptible peanut (af_S) at one (T1), three (T2) and seven (T3) days post-inoculation. The uniquely mapped reads to A. flavus reference genome in the libraries of af_R and af_S at T2 and T3 were subjected to further analysis, with more than 72% of all obtained genes expressed in the eight libraries. Comparison of expression levels both af_R vs. af_S and T2 vs. T3 uncovered 1926 differentially expressed genes (DEGs). DEGs associated with mycelial growth, conidial development and aflatoxin biosynthesis were up-regulated in af_S compared with af_R, implying that A. flavus mycelia more easily penetrate and produce much more aflatoxin in susceptible than in resistant peanut. Our results serve as a foundation for understanding the molecular mechanisms of aflatoxin production differences between A. flavus-R and -S peanut, and offer new clues to manage aflatoxin contamination in crops.