Red light activates H2O2 signal involved in powdery mildew resistance in oriental melon seedlings

Abstract

Melon is one of the most important horticultural crops in Asia. Powdery mildew (PM) is frequently occurred in facility cultivation, which seriously affects its yield and fruit quality of melon. Light signal is the basis of plant growth and development, and appropriate red light (RL) plays an important role in regulating the resistance of plant pathogens. Reactive oxygen species (ROS) also have been shown to be participated in plant defence against pathogen infection. However, whether light is involved in PM resistance through ROS remains unclear. Here, we found that RL+PM treatment significantly enhanced the resistance of PM in melon seedlings, improved NADPH oxidase activity, upregulated respiratory burst oxidase homologue 1 (RBOHD) expression, and increased hydrogen peroxide (H2O2) level. Compared with the PM treatment alone, diphenylene iodonium (DPI)+PM treatment significantly enhanced the sensitivity to PM in melon seedlings and weakened the effect of RL-induced PM resistance. Further studies showed that silencing CmRBOHD significantly inhibited the RL-induced PM resistance by inhibiting H2O2 synthesis. In addition, CmWRKY50 could activate CmRBOHD expression by binding to the promoter of CmRBOHD. Taken together, the results suggest that RL can increase endogenous H2O2 levels and induce the initiation of defence through activation of CmWRKY50, and therefore, when plants are subjected to pathogen stress, higher H2O2 levels in the plants are beneficial for organizing the invasion of pathogens and enhancing powdery mildew resistance.