Nutrition-Associated Processes Govern Fungal Pathogenicity

Fungal pathogens present a major common threat across human communities:they cause disease and death in humans,animals,and global food crops.The development of anti-fungal therapies is hampered primarily by the lack of knowledge about the molecular mechanisms of fungal pathogenicity at the host-pathogen axis.Many studies have shown that nutrition-associated processes such as autophagy and metal homeostasis play essential roles in fungal virulence during systemic infection.During infection,the host immune system often employs nutrition restriction mechanisms to limit microbial proliferation and facilitate the killing and elimination of invading pathogens.Therefore,fast sensing and adaptation to the levels of environmental nutrients are critical if the fungal pathogen is to survive,replicate,and colonize in the host.Fungal cells have evolved numerous precise mechanisms to respond to various levels of nutrient availability.Studies show that fungal cells manipulate the expression of genes involved in nutrient acquisition,autophagosome formation,toxic nutrient detoxification,or cell morphological transition to counter the anti-fungal strategies of the host.This review of the most recent studies of nutrition-related pathways focuses primarily on autophagy,metal homeostasis,and the nutrition-driven morphological switches found in two major human fungal pathogens,Cryptococcus neoformans and Candida albicans.It is a systematic comparison of the functional divergence of nutrition-related genes in the fungal pathogenicity of these evolutionarily distinct but related fungal species.

The pathogenic spectrum of fungal keratitis in northwestern China

I am Na An, from the Shaanxi Key Lab of Ophthalmology, Shaanxi Institute of Ophthalmology,Xi＇an City First Hospital, Xi＇an, Shaanxi Province, China. Fungal keratitis is a severe problem in most developing countries.

Botanicals, as a Sustainable Agroecological Alternative to Synthetic Pesticide for Controlling Leaf Miner (Pinworm) and Fusarium Wilt Disease of Tomato

Tomato (Solanum lycopersicum Mill) is a staple fruit vegetable widely grown worldwide for its rich nutrients including vitamins, minerals and proteins. In spite of its importance, yield and fruit quality in Buea, Cameroon is quite low compared to other countries. Pests and diseases are responsible for these limitations. Those of high importance are pinworm (Tatu absoluta) and Fusarium wilt respectively. Synthetic chemicals have been used to manage this pest/disease on tomato but this has not been very successful because of high cost and unavailability of these chemicals. Botanicals are known to have anti-microbial properties. 10% Leeks and marigold extracts were applied to tomato plants one week after planting. Five treatments were replicated four times in a randomized complete block. They include a control, a synthetic insecticide, leeks extract, marigold extract, and leeks/marigold extracts. Growth and yield parameters were evaluated and data obtained was analysed by descriptive statistics and ANOVA. Results showed that more tomato plant leaves were recorded in the leeks + marigold treatment (54) which differed significantly (P = 0.05) from the control (45). More fruits were harvested in the leeks + marigold treatment (32) which differed significantly (P = 0.05) from the control (18). Pinworm numbers were significantly higher in control (6) (P = 0.05) than the other treatments. Numerous leaf damage was observed in control (20) which differed significantly (P = 0.05) across treatments. More fruit damage was seen in control (14) and differed significantly (P = 0.05) from the other treatments. The least disease incidence was noted in Leeks + Marigold treatment (27.5%), and the most in control (72.5%) which differed significantly (P = 0.05) across treatments. Fusarium oxysporium and Fusarium semitectum were identified. There was a significant difference in pathogen number in control compared to other treatments. Thus leeks and marigold extract increased yield of tomato by mitigating the effects of leaf miner and fusarium wilt.

Variation in Bombyx mori immune response against fungal pathogen Beauveria bassiana with variability in cell wallβ-1,3-glucan

Entomopathogenic fungi are protected by a cell wall with dynamic structure for adapting to various environmental conditions.β-1,3-Glucan recognition proteins activate the innate immune system of insects by recognizing surface molecules of fungi.However,the associations between pathogenicity and the different components of entomopathogenic fungal cell walls remain unclear.Three Beauveria bassiana strains were selected that have significantly differing virulence against Bombyx mori.The molecular mechanisms underlying the immune response in B.mori were investigated using RNA sequencing,which revealed differences in the immune response to different B.bassiana strains at 12 h post-infection.Immunofluorescence assays revealed thatβ-1,3-glucan content had an opposite trend to that of fungal virulence.β-1,3-Glucan injection upregulated BmβGRP4 expression and significantly reduced the virulence of the high-virulence strain but not that of the medium-virulence or low-virulence strains.BmβGRP4 silencing in B.mori with RNA interference resulted in the opposite virulence pattern,indicating that the virulence of B.bassiana was affected by the cell walls’content ofβ-1,3-glucan,which could be recognized by BmβGRP4.Furthermore,interference with the gene CnA(calcineurin catalytic A subunit)involved inβ-1,3-glucan synthesis eliminated differences in virulence between B.bassiana strains.These results indicate that strains of a single species of pathogenic fungi that have differing cell wall components are recognized differently by the innate immune system of B.mori.

A LAMP-assay-based specific microbiota analysis reveals community dynamics and potential interactions of 13 major soybean root pathogens

Soybean root diseases are associated with numerous fungal and oomycete pathogens;however,the community dynamics and interactions of these pathogens are largely unknown.We performed 13 loop-mediated isothermal amplification(LAMP)assays that targeted specific soybean root pathogens,and traditional isolation assays.A total of 159 samples were collected from three locations in the Huang-Huai-Hai region of China at three soybean growth stages(30,60,and 90 days after planting)in 2016.In LAMP results,we found that pathogen communities differed slightly among locations,but changed dramatically between soybean growth stages.Phytophthora sojae,Rhizoctonia solani,and Fusarium oxysporum were most frequently detected at the early stage,whereas Phomopsis longicolla,Fusarium equiseti,and Fusarium virguliforme were most common in the later stages.Most samples(86%)contained two to six pathogen species.Interestingly,the less detectable species tended to exist in the samples containing more detected species,and some pathogens preferentially co-occurred in diseased tissue,including P.sojae–R.solani–F.oxysporum and F.virguliforme–Calonectria ilicicola,implying potential interactions during infection.The LAMP detection results were confirmed by traditional isolation methods.The isolated strains exhibited different virulence to soybean,further implying a beneficial interaction among some pathogens.

Plant Growth Promoting Rhizobacteria as Biological Control Agent in Rice

The use of agrochemical products to combat diseases in crops has adverse effects on the environment and human health. Plant growth promoting rhizobacterium (PGPR) has been increasingly proposed as an eco-friendly alternative in agriculture. PGPRs have beneficial effects not only in promoting plant growth but also have shown their potential as biological control agent, being able to inhibit plant pathogens. Here, we investigated the use of PGPR Paraburkholderia sp. strain SOS3 to provide disease protection in rice (Oryza sativa L.). The antagonistic activity of SOS3 against five fungal pathogens of rice was assessed by dual culture on plates and on rice seedlings. The results showed that on plate assay, SOS3 inhibits the growth of Curvularia lunata, Rhizoctonia solani, Pyricularia oryzae, Helminthosporium oryzae, and Fusarium moniliforme by 17.2%, 1.1%, 8.3%, 32.5%, and 35.4%, respectively. When inoculated on rice seeds, SOS3 promotes seed germination and significantly reduces disease symptoms in plants infected with R. solani. These results suggest that SOS3 has a great potential to be used in rice agriculture to combat the “Sheath Blight” disease.

Determination of Fusarium Species Associated with Onion Plants(Allium cepa)in Field in Burkina Faso Causing Damping-Off and Bulb Rots

Onion (Allium cepa L.) is the second most important vegetable crop in Burkina Faso and provides an important source of income for those involved in the sector. However, producers are facing significant pre-harvest and post-harvest losses. To date, knowledge of major diseases of the crop is limited, limiting the development of effective control strategies. The objective of this study was to test the pathogenicity of some species of Fusarium. To this end, 33 fungal isolates collected from onion plants in 17 localities and belonging to five Fusarium species were used to inoculate onion seeds and bulbs to determine the pathogenic species responsible for damping-off on seedlings and basal bulb rot in Burkina Faso. The virulence of pathogenic isolates was determined according to the percentages of seedling damping-off evaluated 28 Days After Sowing, and the extent of rot in millimetres on inoculated bulbs. The evaluation of isolates on seedlings revealed that the most pathogenic isolates belong to the species F. proliferatum (I29, I21, I37, I33, I31), F. thapsinum (I35) and F. solani (I38) which resulted in 58.33% - 70.83% of seedling damping-off. The most pathogenic isolates on bulbs belong to the species F. proliferatum (I4, I29, I32) and F. oxysporum (I52, I50, I16) which caused 21.67 to 25 mm of rot on bulbs. Isolate I29 was very virulent on both seedlings and bulbs. The isolates of F. fujikuroi species were all low pathogenic on seedlings but one of them, (I27), expressed average pathogenicity on bulbs.

Finns-Kingdom RNA Silencing in Plant-Fungal Pathogen Interactions

Fungal pathogens represent a major group of plant invaders that are the causative agents of many notorious plant diseases. Large quantities of RNAs, especially small RNAs involved in gene silencing, have been found to transmit bidirectionally between fungal pathogens and their hosts. Although host-induced gene silencing （HIGS） technology has been developed and applied to protect crops from fungal infections, the mechanisms of RNA transmission, especially small RNAs regulating trans- kingdom RNA silencing in plant immunity, are largely unknown. In this review, we summarize and discuss recent important findings regarding trans-kingdom sRNAs and RNA silencing in plant-fungal pathogen interactions compared with the well-known RNAi mechanisms in plants and fungi. We focus on the interactions between plant and fungal pathogens with broad hosts, represented by the vascular pathogen Verticillium dahliae and non-vascular pathogen Botrytis cinerea, and discuss the known instances of natural RNAi transmission between fungal pathogens and host plants. Given that HIGS has been developed and recently applied in controlling Verticillium wilt diseases, we propose an ideal research system exploiting plant vasculature-Verticillium interaction to further study trans-kingdom RNA silencing.

What if esca disease of grapevine were not a fungal disease?

Esca disease,which attacks the wood of grapevine,has become increasingly devastating during the past three decades and represents today a major concern in all wine-producing countries.This disease is attributed to a group of systematically diverse fungi that are considered to be latent pathogens,however,this has not been conclusively established.This study presents the first in-depth comparison between the mycota of healthy and diseased plants taken from the same vineyard to determine which fungi become invasive when foliar symptoms of esca appear.An unprecedented high fungal diversity,158 species,is here reported exclusively from grapevine wood in a single Swiss vineyard plot.An identical mycota inhabits wood of healthy and diseased adult plants and presumed esca pathogens were widespread and occurred in similar frequencies in both plant types.Pioneer esca-associated fungi are not transmitted from adult to nursery plants through the grafting process.Consequently the presumed esca-associated fungal pathogens are most likely saprobes decaying already senescent or dead wood resulting from intensive pruning,frost or other mecanical injuries as grafting.The cause of esca disease therefore remains elusive and requires well executive scientific study.These results question the assumed pathogenicity of fungi in other diseases of plants or animals where identical mycota are retrieved from both diseased and healthy individuals.

Taxonomy and pathogenicity of Ceratocystis species on Eucalyptus trees in South China, including C. chinaeucensis sp. nov.

Commercial plantations of Eucalyptus species have been established in South China,especially during the past 20 years,to meet the needs of a rapidly growing national economy.As part of a survey of fungal diseases affecting Eucalyptus species in South China,Ceratocystis species were collected from Eucalyptus plantations in the GuangDong Province.The aims of this study were to identify these Ceratocystis isolates and to test their pathogenicity to Eucalyptus.The most aggressive isolates were also used to screen different species and clones of Eucalyptus for susceptibility to infection under field conditions.The fungi were identified based on morphology and through comparisons of DNA sequence data of the ITS,partialβ-tubulin and TEF-1αgene regions.Morphological and DNA sequence comparisons showed that isolates collected from Chinese Eucalyptus plantations represent two species,C.acaciivora in the C.fimbriata s.l.species complex and a previously undescribed species belonging to the C.moniliformis s.l.species complex,for which the name C.chinaeucensis sp.nov.is provided.In pathogenicity trials,both C.acaciivora and C.chinaeucensis gave rise to lesions on wounded Eucalyptus trees,and the former fungus was most pathogenic.Differences were also observed in the responses of different Eucalyptus clones to inoculation and this could be useful in reducing disease,if C.acaciivora should emerge as a pathogen in the future.

A secretory phospholipase A2 of a fungal pathogen contributes to lipid droplet homeostasis,assimilation of insect-derived lipids,and repression of host immune responses

Secretory phospholipase A2s(sPLA2s)are found in a wide range of organisms from bacteria to higher plants and animals and are involved in varied and cellular pro-cesses.However,roles of these enzymes in microbial pathogens remain unclear.Here,an sPLA2(BbPLA2)was characterized in the filamentous insect pathogenic fungus,Beau-veria bassiana.BbPLA2was exclusively expressed in insect hemolymph-derived cells(hyphal bodies),and its expression was induced by insect-derived nutrients and lipids,and nutrient starvation.High levels of secretion of BbPLA2 were observed as well as its distri-bution in hyphal body lipid drops(LDs).Overexpression of BbPLA2 increased the ability of B.bassiana to utilize insect-derived nutrients and lipids,and promoted LD accumula-tion,indicating functions for BbPLA2 in mediating LD homeostasis and assimilation of insect-derived lipids.Strains overexpressing BbPLA2 showed moderately increased vir-ulence,including more efficient penetration of the insect cuticle and evasion of host im-mune responses as compared to the wild type strain.In addition,B.bassiana-activated host immune genes were downregulated in the BbPLA2 overexpression strain,but upregulated by infections with a△BbPLA2 strain.These data demonstrate that BbPLA2 contributes to LD homeostasis,assimilation of insect-derived lipids,and repression of host immune responses.

Effect of Bacillus Subtilis SY1 on antifungal activity and plant growth

Agriculture soil in some areas of China is seriously damaged due to years of irrational farming practices.Soil-borne disease is a major problem of soil pollution,which affects yield and quality of agricultural products.Ecological remediation of soil is an effective way to solve this problem.In this study,Bacillus subtilis SY1 was successfully used to antagonist several normal fungal pathogens in eggplant.The growth and pathogenic tolerance of the host plant were improved after inoculation.In the seedling test,sprout tendency,accumulative germination percentage,sprout index,and vigour index of seeds increased 24%,24%,35%,and 64%,respectively.Inoculation also made the seedlings stronger and improved their plant-morphologic characters significantly.When infected by fungal pathogen,the activity of protective enzymes in inoculated seedlings improved,which helped lessening membrane damage by superoxide anion.

Two VOZ transcription factors link an E3 ligase and an NLR immune receptor to modulate immunity in rice

Nucleotide-binding leucine-rich repeat(NLR)proteins play critical roles in plant immunity.However,how NLRs are regulated and activate defense signaling is not fully understood.The rice(Oryza sativa)NLR receptor Piz-t confers broad-spectrum resistance to the fungal pathogen Magnaporthe oryzae and the RING-type E3 ligase AVRPIZ-T INTERACTING PROTEIN 10(APIP10)negatively regulates Piz-t accumulation.In this study,we found that APIP10 interacts with two rice transcription factors,VASCULAR PLANT ONEZINC FINGER 1(OsVOZ1)and OsVOZ2,and promotes their degradation through the 26S proteasome pathway.OsVOZ1 displays transcriptional repression activity while OsVOZ2 confers transcriptional activation activity in planta.The osvoz1 and osvoz2 single mutants display modest but opposite M.oryzae resistance in the non-Piz-t background.However,the osvoz1 osvoz2 double mutant exhibits strong dwarfism and cell death,and silencing of both genes via RNA interference also leads to dwarfism,mild cell death,and enhanced resistance to M.oryzae in the non-Piz-t background.Both OsVOZ1 and OsVOZ2 interact with Piz-t.Double silencing of OsVOZ1 and OsVOZ2 in the Piz-t background decreases Piz-t protein accumulation and transcription,reactive oxygen species-dependent cell death,and resistance to M.oryzae containing AvrPiz-t.Taken together,these results indicate that OsVOZ1 and OsVOZ2 negatively regulate basal defense but contribute positively to Piz-t-mediated immunity.

Regulation of biotic interactions and responses to abiotic stresses by MAP kinase pathways in plant pathogenic fungi

Like other eukaryotes,fungi use MAP kinase(MAPK)pathways to mediate cellular changes responding to external stimuli.In the past two decades,three well-conserved MAP kinase pathways have been characterized in various plant pathogenic fungi for regulating responses and adaptations to a variety of biotic and abiotic stresses encountered during plant infection or survival in nature.The invasive growth(IG)pathway is homologous to the yeast pheromone response and filamentation pathways.In plant pathogens,the IG pathway often is essential for pathogenesis by regulating infection-related morphogenesis,such as appressorium formation,penetration,and invasive growth.The cell wall integrity(CWI)pathway also is important for plant infection although the infection processes it regulates vary among fungal pathogens.Besides its universal function in cell wall integrity,it often plays a minor role in responses to oxidative and cell wall stresses.Both the IG and CWI pathways are involved in regulating known virulence factors as well as effector genes during plant infection and mediating defenses against mycoviruses,bacteria,and other fungi.In contrast,the high osmolarity growth(HOG)pathway is dispensable for virulence in some fungi although it is essential for plant infection in others.It regulates osmoregulation in hyphae and is dispensable for appressorium turgor generation.The HOG pathway also plays a major role for responding to oxidative,heat,and other environmental stresses and is overstimulated by phenylpyrrole fungicides.Moreover,these three MAPK pathways crosstalk and coordinately regulate responses to various biotic and abiotic stresses.The IG and CWI pathways,particularly the latter,also are involved in responding to abiotic stresses to various degrees in different fungal pathogens,and the HOG pathway also plays a role in interactions with other microbes or fungi.Furthermore,some infection processes or stress responses are co-regulated by MAPK pathways with cAMP or Ca^(2+)/CaM signaling.Overall,functions of individual MAP kinase pathways in pathogenesis and stress responses have been well characterized in a number of fungal pathogens,showing the conserved genetic elements with diverged functions,likely by rewiring transcriptional regulatory networks.In the near future,applications of genomics and proteomics approaches will likely lead to better understanding of crosstalk among the MAPKs and with other signaling pathways as well as roles of MAPKs in defense against other microbes(biotic interactions).