OsPAL as a key salicylic acid synthetic component is a critical factor involved in mediation of isoproturon degradation in a paddy crop

The chemical isoproturon is widely used for weeding to improve grain productivity in agriculture. Due to its environmental persistence and intensive usage, there is a rising concern regarding isoproturon contamination in food crops that is threatening human health through food chains. This work investigated isoproturon degradation which was affected by salicylic acid, a natural growth regulator in rice plants. Analyses with a salicylic acid synthesis mutant line Ospal (phenylalanine ammonia lyase) showed significantly higher isoproturon accumulation than its wild-type, while spraying exogenous salicylic acid can reverse the phenotype, suggesting that salicylic acid is required to resist isoproturon phytotoxicity and for lower accumulation. This result was well confirmed by three homologue mutants of Arabidopsis which also lost salicylic acid synthetic functions. Profiling genomic loci of isoproturon-exposed wild-type/Ospal rice identified many genes (>2 fold change, p < 0.05) associated with isoproturon degradation and transport enzymes such as cytochromes, glycosyltransferases, glutathione S-transferases and ATP-binding cassettes. To validate the assumption, three novel cytochromes genes were transformed into eukaryotic cells, where isoproturon degradation in the growth medium increased by 16.3, 14.7 and 17.8% after 72 h incubation, respectively. The Liquid Chromatography-Quadrupole-Time of Flight-Mass Spectrometer/Mass Spectrometer was applied to characterizing the isoproturon-degraded metabolites in Ospal plants. A total of 14 metabolites and 18 conjugates in the Ospal and wild-type plants were detected. The concentration of these products was generally increased in Ospal plants, confirming that salicylic acid is necessary for isoproturon degradation in rice plants. Our work highlights the importance of salicylic acid which is potentially used for eliminating isoproturon contamination in food crops when cultivated in the isoproturon-polluted farmland. (C) 2020 Elsevier Ltd. All rights reserved.