Elevated CO2 alters soybean physiology and defense responses, and has disparate effects on susceptibility to diverse microbial pathogens

Summary Increasing atmospheric CO 2 levels have a variety of effects that can influence plant responses to microbial pathogens. However, these responses are varied, and it is challenging to predict how elevated CO 2 ( e CO 2 ) will affect a particular plant-pathogen interaction. We investigated how e CO 2 may influence disease development and responses to diverse pathogens in the major oilseed crop, soybean ( Glycine max [L.] Merr.). Soybeans grown in ambient CO 2 ( a CO 2 , 419 parts per million (ppm)) or in e CO 2 (550 ppm) were challenged with bacterial, viral, fungal, and oomycete pathogens, and disease, pathogen growth, gene expression and molecular plant defense responses were quantified. In e CO 2 , plants were less susceptible to Pseudomonas syringae pv. glycinea ( Psg ) but more susceptible to bean pod mottle virus, soybean mosaic virus, and Fusarium virguliforme . Susceptibility to Pythium sylvaticum was unchanged, although a greater loss in biomass occurred in e CO 2 . Reduced susceptibility to Psg was associated with enhanced defense responses. Increased susceptibility to the viruses was associated with reduced expression of antiviral defenses. This work provides a foundation for understanding of how future e CO 2 levels may impact molecular responses to pathogen challenge in soybean and demonstrates that agents infecting both shoots and roots are of potential concern in future climatic conditions.