Pathogens have long been identified as one of the few major factors for the dramatic loss of crops. This could tightly link to the insufficient immune responses of the crop plants to prevent the infection of pathogens. In recent studies, global warming has worsened this scenario since the high temperature suppresses the plants’ ability to defeat pathogens, mainly by humping the activating broad-spectrum immunity marked by the reduced production of an immune indicator, Pathogenesis-related protein 1 (PR1). Recently, the function of PR1 in the plant immune system has been revealed as a precursor of a cytokine for activating immunity, the CAP-derived peptide 9 in Arabidopsis (AtCAPE9). The protease for releasing immune cytokine AtCAPE9 from PR1 has also been found to be a temperature-vulnerable process. In this study, we hypothesized and demonstrated that the plant immunity suppressed by an elevated temperature is due to the obstruction of the protease activity crucial for AtCAPE9 production. This work includes preliminary studies to design a heat stress treatment procedure for Arabidopsis leaf tissues. It reveals that treating AtCAPE9 could be the key to restoring heat-compromised plant immunity. Furthermore, this research holds a high potential for developing transgenic and non-transgenic approaches to cope with pathogen infection, improving crop yield under the warming globe.