Salicylic acid and jasmonic acid in elevated CO2-induced plant defense response to pathogens

Plants respond to elevated CO2 (eCO2) via a variety of signaling pathways that often rely on plant hormones. In particular, phytohormone salicylic acid (SA) and jasmonic acid (JA) play a key role in plant defense against diverse pathogens at eCO2. eCO2 affects the synthesis and signaling of SA and/or JA and variations in SA and JA signaling lead to variations in plant defense responses to pathogens. In general, eCO2 promotes SA signaling and represses the JA pathway, and thus diseases caused by biotrophic and hemibiotrophic pathogens are typically suppressed, while the incidence and severity of diseases caused by necrotrophic fungal pathogens are enhanced under eCO2 conditions. Moreover, eCO2-induced modulation of antagonism between SA and JA leads to altered plant immunity to different pathogens. Notably, research in this area has often yielded contradictory findings and these responses vary depending on plant species, growth conditions, photoperiod, and fertilizer management. In this review, we focus on the recent advances in SA, and JA signaling pathways in plant defense and their involvement in plant immune responses to pathogens under eCO2. Since atmospheric CO2 will continue to increase, it is crucial to further explore how eCO2 may alter plant defense and host-pathogen interactions in the context of climate change in both natural as well as agricultural ecosystems.