Cinnamaldehyde regulates the synthesis of Alternaria alternata non-host selective toxins by influencing PKS gene expression and oxidoreductase activity

Abstract

Alternaria alternata causes Black Rot disease in fruits and vegetables, and could produce numerous harmful metabolites during pathogen invasion. This study demonstrated that a sub-inhibitory concentration of 0.0125 μl/mL cinnamaldehyde could not inhibit the mycelial growth of A. alternata in Potato dextrose broth (PDB), but the production of non-host selective toxins (NHSTs) was obviously reduced after incubation. The transcriptome data showed that down-regulated genes dominated the differentially expressed genes (DEGs) after cinnamaldehyde treatment, and most DEGs were distributed in metabolic pathways and biosynthesis of secondary metabolites. Four polyketide synthases genes (PksI, PksJ, PksF and PksA) related to mycotoxin biosynthesis in secondary metabolites were screened out after transcriptome sequencing and the expression quantity was significantly down-regulated by cinnamaldehyde incubation. Moreover, the qRT-PCR results showed that cinnamaldehyde inhibited the expression of 4 Pks genes during the growth of A. alternata. In addition, cinnamaldehyde decreased the malondialdehyde (MDA) content but increased the enzymes activities of catalase (CAT) and superoxide dismutase (SOD), the lower reactive oxygen species (ROS) level in the cinnamaldehyde-treated group demonstrated that cinnamaldehyde could improve the antioxidase activities and eliminate excessive ROS production. The results showed that cinnamaldehyde might, through ROS signal transduction, mediate the mycotoxin synthesis of alternariol (AOH), alternariol monomethyl ether (AME) and tenuazonic acid (TEA) in A. alternata.