Remediation of phenanthrene phytotoxicity by the interaction of rice and endophytic fungus P. liquidambaris in practice.

Phenanthrene cannot be effectively degraded in the agricultural production systems and it is greatly hazardous for food safety and human health. In our study, the remediation ability and mechanism of rice and endophytic fungus Phomopsis liquidambaris interaction on phenanthrene in the rice-growing environment were explored using laboratory and pot experiments. The results showed that plant-endophyte interaction had the potential to enhance remediation on phenanthrene contamination in the rice-growing environment. The content of phenanthrene in soil and rice (including leaves, roots, and grains) of the plant-endophyte interaction system was about 42% and 27% lower than of the non-inoculated treatment under 100 mg kg-1 treatment. The mechanism may be related to the improvement of plant growth, root activity, chlorophyll content, ATP energy supply, and antagonistic ability of rice to promote the absorption of phenanthrene in the rice-growing environment, and then the phenanthrene absorbed into the rice was degraded by improving the phenanthrene degrading enzyme activities and gene relative expression levels of P. liquidambaris during plant-endophyte interaction. Moreover, the plant-endophyte interaction system could also promote rice growth and increase rice yield by over 20% more than the control under 50 mg kg-1 treatment. This study indicated a promising potential of the plant-endophyte interaction system for pollution remediation in agriculture.

The Endophytic Fungus Phomopsis liquidambari Increases Nodulation and N2 Fixation in Arachis hypogaea by Enhancing Hydrogen Peroxide and Nitric Oxide Signalling.

The continuous cropping obstacles in monoculture fields are a major production constraint for peanuts. Application of the endophytic fungus Phomopsis liquidambari has increased peanut yields, and nodulation and N2 fixation increases have been considered as important factors for P. liquidambari infection-improved peanut yield. However, the mechanisms involved in this process remain unknown. This work showed that compared with only Bradyrhizobium inoculation, co-inoculation with P. liquidambari significantly elevated endogenous H2O2 and NO levels in peanut roots. Pre-treatment of seedlings with specific scavengers of H2O2 (CAT) and NO (cPTIO) blocked P. liquidambari-induced nodulation and N2 fixation. CAT not only suppressed the P. liquidambari-induced nodulation and N2 fixation, but also suppressed the enhanced H2O2 and NO generation. Nevertheless, the cPTIO did not significantly inhibit the induced H2O2 biosynthesis, implying that H2O2 acted upstream of NO production. These results were confirmed by observations that exogenous H2O2 and sodium nitroprusside (SNP) reversed the inhibition of P. liquidambari-increased nodulation and N2 fixation by the specific scavengers. The transcriptional activities of the symbiosis-related genes SymRK and CCaMK of peanut-Bradyrhizobium interactions also increased significantly in response to P. liquidambari, H2O2 and SNP treatments. The pot experiment further confirmed that the P. liquidambari infection-enhanced H2O2 and NO signalling pathways were significantly related to the increase in peanut nodulation and N2 fixation. This is the first report that endophytic fungus P. liquidambari can increase peanut-Bradyrhizobium interactions via enhanced H2O2/NO-dependent signalling crosstalk, which is conducive to the alleviation of continuous cropping obstacles via an increase in nodulation and N2 fixation.

Endophytic bacteria promote the quality of Lyophyllum decastes by improving non-volatile taste components of mycelia.

Endophytic bacteria are always related to the host different traits, including the secondary metabolites production. However, the effect and mechanism of endophytic bacteria in the mushrooms fruit body on mycelia are still not clear. In this study, we investigated the effect of endophytic bacterial metabolites on the quality of Lyophyllum decastes mycelia. Soluble sugars, starch, protein, free amino acids, 5'-Nucleotides, EUC, and organic acids contents of mycelia were analyzed. We found that endophytic bacterial metabolites significantly increased the contents of soluble sugars, starch, protein, free amino acids, organic acids, and EUC. The present study thus suggests that endophytic bacteria could promote the quality of Lyophyllum decastes by improving non-volatile taste components of mycelia.

Remediation mechanism of endophytic fungus Phomopsis liquidambaris on phenanthrene in vivo.

Phenanthrene can easily be absorbed into the plant from the soil and cannot be effectively degraded in it. Thus, it is greatly hazardous for food safety and human health. In our study, the biodegradability and remediation mechanism of endophytic fungus Phomopsis liquidambaris on phenanthrene in vivo of rice (Oryza sativa L.) was detected. The results showed that the fungus could successfully establish a symbiotic relationship with rice, thus had the potential to degrade phenanthrene absorbed into the plant. Changes of phenanthrene-degrading genes of fungus in the combined system were consistent with the trends of their corresponding enzymatic activities, and the phenanthrene-degrading enzyme activities and gene expression levels in roots of rice were higher than those in the shoot. Moreover, the combined system can enhance bioremediation by increasing root viability, chlorophyll content, and energy supply. The combined system had also significantly increased the PPO activity and SOD activity in shoot compared with the control treatment, while decreased the content of MDA when remediation in vivo. The study on the degradation mechanism of the combined system will help us to increase the practical application potential of endophyte to effectively repair contamination absorbed into plant seedlings.

Mutualistic fungus Phomopsis liquidambari increases root aerenchyma formation through auxin-mediated ethylene accumulation in rice (Oryza sativa L.).

The fungal endophyte Phomopsis liquidambari can improve nitrification rates and alter the abundance and composition of ammonia-oxidizers in the soil rhizosphere of rice. Aerenchyma is related to oxygen transport efficiency and contributes to the enhanced rhizospheric nitrification under flooding conditions. However, whether and how P. liquidambari affects aerenchyma formation is largely unknown. We therefore conducted pot and hydroponic experiments to investigate the changes of aerenchyma area, ethylene and indole-3-acetic acid (IAA) levels in rice with or without P. liquidambari infection. Our results showed that the larger aerenchyma area in rice roots with P. liquidambari inoculation was associated with markedly up-regulated expression of genes related to aerenchyma formation. Meanwhile, P. liquidambari inoculation substantially elevated root porosity (POR) and radial oxygen loss (ROL), leading to the enhancement of oxidation-reduction potential (ORP) under pot condition. Besides, P. liquidambari significantly increased IAA and ethylene levels in rice by stimulating the expression of genes involved in auxin and ethylene biosyntheses. Furthermore, auxin that partly acting upstream of ethylene signalling played an essential role in P. liquidambari-promoted aerenchyma formation. These results verified the direct contribution of P. liquidambari in promoting aerenchyma formation via the accumulation of IAA and ethylene in rice roots, which provides a constructive suggestion for improving hypoxia tolerance through plant-endophyte interactions.

Potential of endophytic fungus Phomopsis liquidambari for transformation and degradation of recalcitrant pollutant sinapic acid.

The biodegradation potential of sinapic acid, one of the most representative methoxy phenolic pollutants presented in industrial wastewater, was first studied using an endophytic fungus called Phomopsis liquidambari. This strain can effectively degrade sinapic acid in flasks and in soil and the possible biodegradation pathway was first systematically proposed on the basis of the metabolite production patterns and the identification of the metabolites by GC-MS and HPLC-MS. Sinapic acid was first transformed to 2,6-dimethoxy-4-vinylphenol that was further degraded via 4-hydroxy-3,5-dimethoxybenzaldehyde, syringic acid, gallic acid, and citric acid which involved in the continuous catalysis by phenolic acid decarboxylase, laccase, and gallic acid dioxygenase. Moreover, their activities and gene expression levels exhibited a 'cascade induction' response with the changes in metabolic product concentrations and the generation of fungal laccase significantly improved the degradation process. This study is the first report of an endophytic fungus that has great potential to degrade xenobiotic sinapic acid, and also provide a basis for practical application of endophytic fungus in the bioremediation of sinapic acid-contaminated industrial wastewater and soils.