Melatonin elevated Sclerotinia sclerotiorum resistance via modulation of ATP and glucosinolate biosynthesis in Brassica rapa ssp. pekinensis.

Sclerotinia stem rot is a common disease found in Brassica rapa that is caused by the necrotic plant pathogen Sclerotinia sclerotiorum. Melatonin (MT) has known biological activity and effectively relieved this type of Sclerotinia stem rot in B. rapa. To better understand the mechanisms behind MT-induced S. sclerotiorum resistance in B. rapa, we performed both proteomic and metabolomic analysis. Our results showed that during S. sclerotiorum infection, thiamine synthesis was activated and defended against it. In infected leaves, ribosomal synthesis-related proteins responded positively to MT treatment. Integrated proteomic and metabolomic analysis showed that amino acid metabolism was activated by MT treatment. After MT treatment, adenosine-triphosphate (ATP) content and the activity of antioxidant enzymes were both increased in B. rapa infected leaves. Cysteine synthase, sulfur transfer-related proteins, and glucosinolate (GS) were all increased after MT treatment in infected B. rapa leaves. Taken together, these results indicated that B. rapa leaves promoted thiamine formation to defend against S. sclerotiorum infection. Moreover, MT helped further induce antioxidant activation in B. rapa in an ATP-dependent manner and stimulating GS biosynthesis to well inhibit the S. sclerotiorum infection. SIGNIFICANCE: Melatonin (MT) has biological activity and effectively relieved the Sclerotinia stem rot of Brassica rapa caused by the necrotic plant pathogen Sclerotinia sclerotiorum. In order to reveal the molecular mechanisms of MT-induced S. sclerotiorum resistance in B. rapa, comprehensive proteomic and metabolomic analyses were conducted. The integration analysis of omic-data illustrated that the modulation of ATP and glucosinolate biosynthesis induced by MT administration helped to defend the infection of S. sclerotiorum in B. rapa. Our results will provide insights into MT-induced anti-fungal mechanism and therapeutic strategies to mitigate Sclerotinia stem rot of B. rapa, thereby increasing plant yield and decreasing economic losses.