Entomopathogenic fungi play a pivotal role in the regulation of insect populations in nature, and representative species have been developed as promising environmentally friendly mycoinsecticides. ...Recent advances in the genome biology of insect pathogenic fungi have revealed genomic features associated with fungal adaptation to insect hosts and different host ranges, as well as the evolutionary relationships between insect and noninsect pathogens. By using species in the Beauveria and Metarhizium genera as models, molecular biology studies have revealed the genes that function in fungus-insect interactions and thereby contribute to fungal virulence. Taken together with efforts toward genetic improvement of fungal virulence and stress resistance, knowledge of entomopathogenic fungi will potentiate cost-effective applications of mycoinsecticides for pest control in the field. Relative to our advanced insights into the mechanisms of fungal pathogenesis in plants and humans, future studies will be necessary to unravel the gene-for-gene relationships in fungus-insect interactive models.
Quinones are widely distributed in nature and exhibit diverse biological or pharmacological activities; however, their biosynthetic machineries are largely unknown. The bibenzoquinone oosporein was ...first identified from the ascomycete insect pathogenBeauveria bassiana>50 y ago. The toxin can also be produced by different plant pathogenic and endophytic fungi with an array of biological activities. Here, we report the oosporein biosynthetic machinery in fungi, a polyketide synthase (PKS) pathway including seven genes for quinone biosynthesis. The PKS oosporein synthase 1 (OpS1) produces orsellinic acid that is hydroxylated to benzenetriol by the hydroxylase OpS4. The intermediate is oxidized either nonenzymatically to 5,5′-dideoxy-oosporein or enzymatically to benzenetetrol by the putative dioxygenase OpS7. The latter is further dimerized to oosporein by the catalase OpS5. The transcription factor OpS3 regulates intrapathway gene expression. Insect bioassays revealed that oosporein is required for fungal virulence and acts by evading host immunity to facilitate fungal multiplication in insects. These results contribute to the known mechanisms of quinone biosynthesis and the understanding of small molecules deployed by fungi that interact with their hosts.
•Biocontrol potential of entomopathogenic fungi depends on fungal virulence and field adaptation.•Genetic improvement of fungal biocontrol potential needs new knowledge in genomics and molecular ...biology.•Genomic and molecular studies in China speed up for creating new-generation mycoinsecticides.
Entomopathogenic fungi, such as Beauveria bassiana and Metarhizium anisopliae, are environmentally friendly biocontrol agents (BCAs) against various arthropod pests. We provide an overview to the past-decade advances in fungal BCA research and application in China. Since 1960s, fungal BCAs have been mass-produced for application and at present, thousands of tons of their formulations are annually applied to control forest, agricultural, greenhouse and grassland insect pests throughout the country. Apart from technical advances in mass production, formulation and application of fungal BCAs, basic studies on the genomics, molecular biology, genetic engineering and population genetics of fungal entomopathogens have rapidly progressed in the past few years in China. The completed genomic studies of M. anisopliae, Metarhizium acridum, B. bassiana and Cordyceps militaris provide profound insights into crucial gene functions, fungal pathogenesis, host–pathogen interactions and mechanisms involved in fungal sexuality. New knowledge gained from the basic studies has been applied to improve fungal virulence and stress tolerance for developing more efficacious and field-persistent mycoinsecticides by means of microbial biotechnology, such as genetic engineering. To alleviate environmental safety concerns, more efforts are needed to generate new data not only on the effects of engineered BCAs on target and non-target arthropods but also on their potential effects on gene flow and genetic recombination before field release.
•IC of small watershed was applied to quantify the spatial variation in sediment connectivity.•Significant spatial variation and autocorrelation were detected in IC on the Loess Plateau.•Vegetation ...and climatic factors dominated the spatial variation in IC.•The influences of different factors on IC varied with latitude.
Sediment connectivity likely varies greatly over space, which further affects the processes of hydrology, erosion and sediment delivery of watershed. Small watershed is the basic geomorphologic unit for soil and water conservation. Few studies have been performed to quantify the spatial variation in sediment connectivity of small watershed at regional transect. Six typical small watersheds distributed from south to north on the Loess Plateau were selected as a regional transect to investigate the spatial variation in sediment connectivity and its influencing factors. In this study, the widely utilized index of connectivity (IC) was used to investigate the spatial variation of sediment connectivity in small watersheds. The source-sink landscape index reflecting the source or sink effect of landscape pattern on soil erosion process was utilized to compute the weights for IC. The redundancy analysis (RDA) was applied to identify the main influencing factors contributing to the spatial variation in IC. The results showed that IC increased from south to north (ranged from −2.02 to 1.76). A significant positive spatial autocorrelation was detected in IC of small watershed on the Loess Plateau (p < 0.05). The relationships between IC and environmental factors differed between different small watersheds. The results of RDA showed that the contributions of different influencing factors varied along the tested transect. The relative contributions of climate factors and vegetation factors to IC declined whereas that of land surface factors raised with latitude. Vegetation and climate were the main factors controlling the spatial variation in IC. The results are helpful to understand the spatial heterogeneity of soil erosion and evaluate the conservation benefit of vegetation restoration in semi-arid region.
Insect pathogenic fungi produce a plethora of insecticidally and pharmaceutically active compounds, including 39 cyclohexadepsipeptide destruxins (dtxs). Even though dtxs were first discovered more ...than 50 y ago, the genes responsible for their biosynthesis were unknown until this study. Based on our comparative genomic information and targeted gene disruptions, we report the gene cluster for dtx biosynthesis in the insect pathogen Metarhizium robertsii. The nonribosomal peptide synthetase DtxS1 has six adenylation domains, two of which are capable of selecting different amino acids to synthesize dtx B and its analogs. The cytochrome P450 enzyme DtxS2 converts dtx B into other dtxs by a chain of reactions, each producing a new derivative. The aldo-keto reductase DtxS3 and aspartic acid decarboxylase DtxS4 are responsible for the conversion and provision of the first and last substrates for the dtx assembly line, respectively. Insect bioassays showed that dtxs could suppress both cellular and humoral immune responses thereby assisting fungal propagation in insects. The differing abilities of Metarhizium species to produce toxins is dependent on the presence of the dtxS1 gene. The toxigenic species are capable of killing multiple orders of insects, whereas the nontoxigenic Metarhizium spp. have narrow host ranges. Thus, the acquisition or retention of the dtx biosynthesis gene cluster in Metarhizium lineages has been coordinated with the evolution of fungal host specificity. The data from this study will facilitate the development of dtxs as bioinsecticides or Pharmaceuticals.
The lysin motif (LysM) containing proteins can bind chitin and are ubiquitous in various organisms including fungi. In plant pathogenic fungi, a few LysM proteins have been characterized as effectors ...to suppress chitin-induced immunity in plant hosts and therefore contribute to fungal virulence. The effector mechanism is still questioned in fungus-animal interactions. In this study, we found that LysM proteins are also present in animal pathogenic fungi and have evolved divergently. The genome of the insect pathogen Beauveria bassiana encodes 12 LysM proteins, and the genes were differentially transcribed by the fungus when grown in different conditions. Deletion of six genes that were expressed by the fungus growing in insects revealed that two, Blys2 and Blys5, were required for full fungal virulence. Both proteins could bind chitin and Blys5 (containing two LysM domains) could additionally bind chitosan and cellulose. Truncation analysis of Blys2 (containing five LysM domains) indicated that the combination of LysM domains could determine protein-binding affinity and specificity for different carbohydrates. Relative to the wild-type strain, loss of Blys2 or Blys5 could impair fungal propagation in insect hemocoels and lead to the upregulation of antifungal gene in insects. Interestingly, the virulence defects of ΔBlys2 and ΔBlys5 could be fully restored by complementation with the Slp1 effector from the rice blast fungus Magnaporthe oryzae. In contrast to Slp1 and Blys2, Blys5 could potentially protect fungal hyphae against chitinase hydrolysis. The results of this study not only advance the understanding of LysM protein evolution but also establish the effector mechanism of fungus-animal interactions.
•Soil surface roughness decreased significantly with land degradation degree.•Soil surface roughness was increased by incorporated straw residual, particularly in moderate and strong degraded ...croplands.•Changes in soil surface roughness were controlled by a combination of soil and vegetation properties and incorporated straw.•Sediment connectivity decreased while relative elevation attribute increased with soil surface roughness.
Changes in soil surface roughness (SSR) are not only closely associated with the characteristics of the underlying surface but also play a vital role in hydrological and soil erosion processes. SSR of degraded croplands is likely affected by the residual of incorporated straw, however, few studies have been focused on this topic. This study was conducted to investigate the changes in SSR of sloping croplands with different land degradation degrees under straw incorporated and without straw incorporated treatments, and determine the dominant factors attributing to these changes in the black soil region of Northeast China. SSR was determined by a photogrammetry technique and the dominant influencing factors were identified by redundancy analysis. The results showed that SSR were decaying by land degradation. Compared to non-degraded croplands, SSR of light, moderate and heavy degraded croplands decreased by 10.4 %, 11.3 %, 23.3 % and 13.8 %, 16.7 %, 31.9 % for straw incorporated and without straw incorporated treatments, respectively. The improvement of SSR was mediated by residual of incorporated straw. Compared to the treatment of without straw incorporation, SSR of straw incorporated treatment increased by 29.4 %, 30.5 %, 32.7 %, and 33.3 % for non, light, moderate and heavy degraded croplands, respectively. Change in SSR was modulated by soil properties, crop characteristics, and residual of incorporated straw. Change of SSR was dominantly controlled by water-stable aggregate (WSA), penetration resistance (PR), soil organic matter (SOM), structure stability index (SSI), mean weight diameter (MWD), root mass density (RMD), litter mass density (LMD) and amount of incorporated straw residual. The increase in SSR was linear with SSI, SOM, RMD and LMD, and logarithmic with MWD and WSA. The measured SSR could be well estimated by WSA, SOM, PR and RMD (R2 = 0.82). SSR could affect hydrological and erosion processes of croplands by reducing sediment connectivity and increasing land surface storage of runoff. The results of this study are helpful in understanding the spatial heterogeneity of SSR at the hillslope scale.
The exopolysaccharide galactosaminogalactan (GAG) has been well characterized in Aspergilli, especially the human pathogen Aspergillus fumigatus. It has been found that a five-gene cluster is ...responsible for GAG biosynthesis in Aspergilli to mediate fungal adherence, biofilm formation, immunosuppression or induction of host immune defences. Herein, we report the presence of the conserved GAG biosynthetic gene cluster in the insect pathogenic fungus Metarhizium robertsii to mediate either similar or unique biological functions. Deletion of the gene cluster disabled fungal ability to produce GAG on germ tubes, mycelia and appressoria. Relative to the wild type strain, null mutant was impaired in topical infection but not injection of insect hosts. We found that GAG production by Metarhizium is partially acetylated and could mediate fungal adherence to hydrophobic insect cuticles, biofilm formation, and penetration of insect cuticles. In particular, it was first confirmed that this exopolymer is responsible for the formation of appressorium mucilage, the essential extracellular matrix formed along with the infection structure differentiation to mediate cell attachment and expression of cuticle degrading enzymes. In contrast to its production during A. fumigatus invasive growth, GAG is not produced on the Metarhizium cells harvested from insect hemocoels; however, the polymer can glue germ tubes into aggregates to form mycelium pellets in liquid culture. The results of this study unravel the biosynthesis and unique function of GAG in a fungal system apart from the aspergilli species.
Metarhizium is a group of insect-pathogenic fungi that can produce insecticidal metabolites, such as destruxins. Interestingly, the acridid-specific fungus Metarhizium acridum (MAC) can kill locusts ...faster than the generalist fungus Metarhizium robertsii (MAA) even without destruxin. However, the underlying mechanisms of different pathogenesis between host-generalist and host-specialist fungi remain unknown. This study compared transcriptomes and metabolite profiles to analyze the difference in responsiveness of locusts to MAA and MAC infections. Results confirmed that the detoxification and tryptamine catabolic pathways were significantly enriched in locusts after MAC infection compared with MAA infection and that high levels of tryptamine could kill locusts. Furthermore, tryptamine was found to be capable of activating the aryl hydrocarbon receptor of locusts (LmAhR) to produce damaging effects by inducing reactive oxygen species production and immune suppression. Therefore, reducing LmAhR expression by RNAi or inhibitor (SR1) attenuates the lethal effects of tryptamine on locusts. In addition, MAA, not MAC, possessed the monoamine oxidase (Mao) genes in tryptamine catabolism. Hence, deleting MrMao-1 could increase the virulence of generalist MAA on locusts and other insects. Therefore, our study provides a rather feasible way to design novel mycoinsecticides by deleting a gene instead of introducing any exogenous gene or domain.
•The effects of slope position on soil erodibility were quantified by multi-indicators.•Different trends were detected in nine erodibility indicators with slope position.•CSEI increased from upper to ...middle and then decreased quickly to lower position.•SOM and PCth were the dominant factors influencing the variation in CSEI.
The position of the rolling hill slope has considerable effects on soil properties and crop growth via the spatial heterogeneity of erosion intensity, which in turn probably impacts soil erodibility. However, few studies have been carried out to quantify the potential effects of slope position on soil erodibility indicators on long gentle slope. This study aimed to quantify the spatial variations in soil erodibility indicators of soil cohesion (Coh), saturated hydraulic conductivity (Ks), mean weigh diameter (MWD), mean number of drop impact (MND), soil penetration resistance (PR), soil structural stability index (SSI), soil erodibility of K factor, slaking rate (SR), organic matter content (SOC) and a comprehensive soil erodibility index (CSEI) on two typical rolling hill slopes in northeast China. Soil properties, root mass density (RMD) and litter mass density (LMD) were determined to explain the spatial change of soil erodibility indicators with slope position. The results showed that Coh, MWD, MND, PR and SOC declined from upper to middle, and then increased continuously until to lower position. The distinctly opposite changes were found in Ks and SR with slope position. No distinct variation was observed in K factor and SSI with slope position. For both two slopes, CSEI increased from upper to middle, and then decreased quickly to lower position. Compared to middle position, the mean reduces of two tested hillslopes were 51.72%, 14.74%, 24.28% and 72.52% for upper to lower positions, respectively. The results of Path analysis showed that SOM was the main factors contributing to the variation of CSEI with slope position. This study confirmed that the middle position is the most susceptible area to erosion on long gentle rolling hillslope. The results are helpful to understand the spatial variation in soil erosion intensity and design soil conservation measures on long gentle slopes.
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