Fig. 8.

Response mechanism of ginseng to rusty root symptoms. “?” means not validated; The solid arrows indicate the direct action and the dotted arrows indicate the indirect action. Environmental stress induces oxidative stress, which activates the ETI system and stimulates the synthesis of SA, MeJA, and ABA in ginseng tissues. SA and MeJA induce the accumulation of phenolic, alkaloid, and alcohol metabolites. SA and MeJA also induce lipid and fatty acid metabolism and enhance membrane stability against stress. The production of antioxidant enzymes such as CAT and SOD and the peroxisome regulation affect ROS accumulation in tissues. Meanwhile, DEGs in PTI and ETI in ginseng epidermal tissues may promote PR proteins' production and hypersensitive responses against external stresses. The activation of the phenylpropanoid biosynthesis pathway enhances the production of phenolic metabolites on the one hand. It may increase the accumulation of lignin and promote the cell wall's reinforcement on the other hand. The reinforcement of the cell wall and the enhancement of membrane stability together constitute a physical defense in ginseng tissues