Salicylic acid enhances the resistance of Neoporphyra haitanensis to pathogen Vibrio mediterranei 117-T6

The economically important seaweed Porphyra are often infected by various diseases during sea farming. As one of the most important phytohormones in disease resistance, the protective effect of salicylic acid (SA) on Neoporphyra haitanensis during Vibrio mediterranei 117-T6 infection was investigated by biochemical methods and transcriptomic profile analysis. The addition of exogenous SA at a moderate concentration alleviated disease caused by the pathogenic bacteria. SA enhanced the photosynthetic activity of thalli by upregulating genes of the photosynthetic system along with genes associated with carbon fixation. A moderate release of H2O2 stimulated by SA was observed, which may be due to the upregulation of the photorespiratory C2 cycle and the inhibition of catalase activity. SA treatment enhanced the activity and transcription of antioxidant enzymes in the glutathione-ascorbate (GSH-AsA) cycle involved in balancing the redox system. In addition, the levels of multiple carotenoids were increased in N. haitanensis thalli, and genes involved in their synthesis were upregulated. The results suggest that exogenous SA may enhance the defense of N. haitanensis against pathogen attack by the release of H2O2. However, to avoid oxidative stress, alga can establish redox balance by activating the GSH-AsA cycle and by regulating the generation of carotenoids. In summary, this study indicates that N. haitanensis may have evolved mechanisms to respond to SA stimulation and protect against invading pathogens. Our research can provide valuable information for the farming of healthy N. haitanensis.