Integrated transcriptomic-metabolomic analysis reveals that cinnamaldehyde exposure positively regulates the phenylpropanoid pathway in postharvest Satsuma mandarin (Citrus unshiu)

Abstract

Previously, wax + cinnamaldehyde (WCA) was proven to be able to effectively alleviate fruit decay and induce resistance in harvested Satsuma mandarin (Citrus unshiu). However, the potential molecular mechanism is largely unknown. In the present study, transcriptomics, metabolomics and biochemical analyses were combined to clarify this process. Transcriptomic analysis revealed that the expression of genes involved in secondary metabolites and related to pathogenesis and the phenylpropanoid pathway were significantly influenced by WCA treatment. In addition, metabolite profiling revealed that metabolites in the phenylpropanoid pathway were also predominantly impacted after WCA treatment. Correspondingly, enzymatic activities and gene expression involved in the phenylpropanoid pathway were positively regulated, especially in the first 24 h, resulting in increased levels of total phenolics, flavonoids and other secondary metabolites. Fruit inoculation experiments showed that WCA treatment significantly reduced the development of citrus green mold and sour rot while having no adverse effects on the edible quality of the tested citrus fruit. Our study confirms the potential role of WCA exposure in citrus to induce resistance through the phenylpropanoid pathway.