Debaryomyces nepalensis enhances suberin deposition in citrus fruit wound by facilitating the synthesis of cinnamic acid and its derivatives

Mechanical damage to citrus fruit is inevitable when picking, transporting, storing, and marketing. Previous studies have shown that citrus fruit have the ability to wound healing. Suberin is the signature substance for wound healing. This study investigates the effect of Debaryomyces nepalensis treatment on promoting citrus fruit wound healing and its mechanism. The effect of D. nepalensis was assessed through the examination of changes in suberin content at the wounds of citrus fruit treated with D. nepalensis using an ortho-fluorescent microscopy, as well as the occurrence of green mold in fruit treated with D. nepalensis. Wound samples treated with D. nepalensis for 3 d and those healed naturally over the same period were analyzed through transcriptome and metabolome evaluations. Results showed significant suberin accumulation in treated wounds compared to natural healing. D. nepalensis notably improved the healing process and reduced green mold disease incidence and lesion diameter. Additionally, D. nepalensis activated the phenylpropane biosynthesis pathway, which led to the upregulation of 34 genes, including COMT, HCT, CAD, and PAL. Consequently, this activation also resulted in a significant increase in the content of phenolic acids, including cinnamic acid and its derivatives, caffeic acid and chlorogenic acid. Moreover, the exogenous application of these phenolic acids further promoted wound healing and reduced green mold incidence. In conclusion, D. nepalensis activates the phenylpropane biosynthesis pathway, enhances the expression of crucial genes like COMT, and increases the content of substances such as caffeic acid to facilitate wound healing in citrus fruit.