| Fungal endophytes and saprotrophs generally play an important ecological role within plant tissues and dead plant material.Some studies have investigated relationships among endophytes and saprobes and it has been hypothesised that fungal endophytes become saprobes following the senescence of host tissue.Our previous research indicated that an endophytic fungus,Phomopsis liquidambari B3,can establish a mutualistic symbiotic relationship with rice,promoting the growth and disease-resistant,enhancing the adversity ability,of rice.In saprophytic phase,B3 has the capability of rapidly decomposing plant litter,promoting nutrient cycling and optimizing the soil microenvironment.However,it is still short of adequate research on how fungal endophytes switch to saprotrophs in the the senescence of plant tissue.To clarify this scientific problem,it will be of great importance in understanding the relationship between endophyte and plant,and the diversity of endophyte.The transcriptome is made up of the subset of genes active in a selected tissue and species.Understanding the dynamics of the transcriptome is essential for interpreting phenotypic variation caused by combinations of genotypic and environmental factors.We inoculated P.liquidambari B3 on the the surface of rice callus for simulating symbiotic system,in the liquid litter medium for simulating saprotrophic system,on the ordinary carbon source medium for pure culture.Extracted RNA samples of B3 under different habitats for Illumina sequencing.It is found that under different host environment,the genes related to carbohydrate metabolism play a vital role in the processes of fungus symbiosis and saprotrophy.Genes mainly performing molecular function of catalysis and transporter,and participating in metabolic processes in the cell and on the cellular membrane,it provides the material base for fungus symbiosis and saprotrophy.As far as we know,it is the first time to study and acquired the whole transcriptome information of P.liquidambari by RNA-seq technology.Our experimental results provide more wide range of sequence resources for study filamentous endophytic fungus B3.Analyzed the differentially expressed genes of P.liquidambari B3 under different host environment,simulating symbiotic system,simulating saprotrophic system and pure culture,by Digital Gene Expression Profiling.Validation of the sequencing results by qRT-PCR.It is found that under the condition of symbiosis,in order to adapt to the host,B3 synthesize a large amount of secondary metabolites and ribosome.The genes of Citrate cycle pathway,a critical pathway of energy metabolism,were up regulated.Under the condition of saprotrophy,B3 be forced to decompose organic matter remaining in the litter due to the host lack the nutrition which can be used directly.Enhancing the katabolism capability of hardly degradable organic compounds,increasing in demand of carbon source,such as carbohydrate,resulting in the genes of carbohydrate metabolism were up regulated.This research analyzed the differentially expressed genes of P.liquidambari in the different survival habitats,explained the interrelation of fungus symbiosis and saprotrophy from genetic perspective.The katabolism capability of hardly degradable organic compounds was enhanced and the degrading enzyme related to compounds was secreted when P.liquidambari B3 under the condition of saprotrophy.We added 4-hydroxybenzoic acid to the flask shaking medium of P.liquidambari B3,inducing laccase production.Biomass concentration,laccase enzyme activity and sucrose content at different times were measure.The experimental results show that the production of laccase is partially associated with the growth of P.liquidambari B3.The Logistic equation is used to represent cell growth,the Luedeking-Piret equation indicates laccase production and the Luedeking-Piret-Like equation signifies substrate consumption.Applied MATLAB software to nonlinear fitting experimental data and equations,we got the optimal parameters and the fermentation kinetic model.Validation experiments found that the errors between the calculated values and the experimental values were mostly less than 10%,indicating that the fermentation kinetic model can describe the actual fermentation process of P.liquidambari B3 felicitously.The results have a guiding role in P.liquidambari B3 produce laccase by fermentation and its industrial enlargement.Food waste is the most difficult waste to manage because the high treatment costs and the risk of environmental contamination.Wheat straw burning has become an increasingly discussed topic in recent years because the air pollution caused by it.However,food waste and wheat straw contain high amounts of nutrient elements,efficient utilization of these waste can improve the environment by lessening airborne pollutant emission and the amount of waste that must be landfilled.It is well known that use of low cost and abundant waste materials in microbial fermentations can reduce product costs.We aimed to use these resources while improving laccase production by the endophytic fungus P.liquidambari B3.We cultured P.liquidambari B3 in medium containing food waste and wheat straw as the main nitrogen and carbon sources,respectively,simulating saprotrophic system.We optimized the fermentation conditions by response surface methodology(RSM),using a Box-Behnken design for RSM I and a central composite design for RSM II.Optimization resulted in an 11.07-fold(1.98-fold RSM I;5.59-fold RSM II)increase in laccase yield compared with that before optimization.The model was validated by mathematical evaluations and by comparisons between predicted and experimental values.Under optimized conditions,53.76%of lignin in wheat straw was degraded.By optimizing fermentation conditions and using multiple bioresources,laccase production by this fungus was increased.These results provide the foundation for future research and for scaled-up laccase production.The accumulation of phenolic acids in soil is one of the main problems associated with continuous cropping of peanut.Although laccases secreted by fungi can efficiently transform phenolic acids,there are few reports on the use of these enzymes to bioremediate continuous cropping soil.Food waste and wheat straw are waste products,however,they could be used productively as resources for laccase production by the endophytic fungus P.liquidambari B3.We cultured P.liquidambari B3 in medium containing food waste as the main nitrogen source and wheat straw as the main carbon source,simulating saprotrophic system.In order to study the effects of fermentation liquid on phenolic acid degradation,rhizosphere soil microbial communities and peanut seedling growth,the fermentation product,which had high laccase activity,was added to continuously cropped soil of peanut.The concentration of 4-hydroxybenzoic acid,vanillic acid and coumaric acid in soil had decreased by 57.4,52.5 and 49.4%compared with no-treatment control during 28 days.Analysis of denaturing gradient gel electrophoresis(DGGE)profiles showed that the bacterial and fungal community structures in rhizosphere soil were affected by changes in the phenolic acids concentration.The biomass of peanut plants and the number of root nodules were increased 68.3%and 5.9-fold,respectively.These results showed that the laccase product reduced the accumulation of phenolic acids in soil,the decrease in phenolic acids concentration and the increase in certain dominant microorganisms promoted peanut seedling growth and nodulation.This technology provides a new strategy for bioremediation of continuous cropping soil,while simultaneously reducing waste and protecting the environment. |
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