Biodegradation of a model allelochemical cinnamic acid by a novel endophytic fungus Phomopsis liquidambari

• Phomopsis liquidambari degraded cinnamic acid effectively in MSM and in soil.
• The biodegradation route by an endophytic fungus was first proposed.
• The expressions of padB3, lacB3 and pcaB3 were induced by different metabolites.
• P. liquidambari laccase improved the degradation rate.
• P. liquidambari alleviated plant allelopathic stress caused by cinnamic acid.

Cinnamic acid, as a model phenolic allelochemical, can be widely found in continuous cropping soils, and its accumulation often causes a decline in growth, yield and crop quality. In this study, endophytic fungus Phomopsis liquidambari could effectively degrade allelochemical cinnamic acid as its sole source of carbon and energy for growth, and glucose did not significantly affect its degradation efficiency. The degradation pathway of cinnamic acid was proposed based on metabolites identified by GC–MS and HPLC-MS. Cinnamic acid was initially transformed to styrene that was further degraded via benzaldehyde, benzoic acid, 4-hydroxybenzoic acid and protocatechuic acid, which included the involvement of phenolic acid decarboxylase, laccase, hydroxylase and protocatechuate 3,4-dioxygenase. Their activities and gene transcription dynamics were consistent with the changes in related intermediate product concentrations. Moreover, the generation of laccase significantly improved the degradation rate of cinnamic acid. Further study found that even in a complex soil environment, this strain could also efficiently degrade cinnamic acid and then improve the growth of peanut seedlings. Therefore, these results indicated that P. liquidambari could be considered a suitable candidate for practical application to mitigate the allelopathic stress caused by cinnamic acid in continuous cropping soils.