Proteomic analysis of Mn-induced resistance to powdery mildew in grapevine

Previous studies documented that metal hyperaccumulation armours plants with direct defences against pathogens. In the present study, it was found that high leaf Mn concentrations (<2500 µg g(-1)) induced grapevine resistance to powdery mildew [Uncinula necator (Schw.) Burr]. Manganese delayed pathogen spreading after powdery mildew (PM) inoculation, but did not directly inhibit pathogen growth on a long-term basis. It was postulated that the grapevine resistance resulted from the induction of protective mechanisms in planta. To test this hypothesis, the proteome profile was analysed by Difference Gel Electrophoresis (DIGE) methods to identify proteins that are putatively involved in pathogen resistance. A high Mn concentration caused little oxidative pressure in grapevine, but oxidative stress was deeply enhanced by PM stress. Except for a few proteins that were related to oxidative pressure and proteins specially regulated by Mn or PM, most of the detected proteins exhibited similar changes under excess Mn stress and under PM stress, suggesting that similar signalling processes mediate the responses to the two stresses. As well as PM stress, high leaf Mn concentration significantly enhanced salicylic acid concentration and increased the expression of proteins involved in ethylene and jasmonic acid synthesis. The proteins related to pathogen resistance were also enhanced by excess Mn, including a PR-like protein, an NBS-LRR analogue, and a JOSL protein, and this was accompanied by the increased activity of phenylalanine ammonia lyase. It was concluded that high leaf Mn concentration triggered protective mechanisms against pathogens in grapevine.