Abstract
Climate change and the associated increase in atmospheric CO2 levels may affect the severity of plant diseases and threaten future crop yields. Here, we compared responses of the model plant Arabidopsis thaliana to leaf and root pathogens with hemi-biotrophic or necrotrophic infection strategies under pre-industrial, current, and future atmospheric CO2 conditions. Defenses against biotrophs are generally regulated by salicylic acid (SA) signaling, whereas jasmonic acid (JA) signaling controls defenses against necrotrophs. Under the CO2 conditions tested, basal expression of the JA-responsive marker gene PDF1.2 increased at increasing CO2 concentrations. The SA-responsive marker genes ICS1 and FRK1 showed an opposite behavior, being lower expressed under high CO2 and higher expressed under low CO2, respectively. Accordingly, plants showed enhanced resistance to the necrotrophic leaf pathogen Botrytis cinerea under high CO2, while resistance to the hemi-biotrophic leaf pathogen Pseudomonas syringae pv. tomato was reduced. The opposite was true for plants grown under low CO2. Disease severity caused by the soil-borne pathogens Fusarium oxysporum f.sp. raphani and Rhizoctonia solani was similar under all CO2 conditions tested. Collectively, our results stress the notion that atmospheric CO2 impacts the balance between SA- and JA-dependent defenses and concomitant resistance against foliar (hemi)biotrophic and necrotrophic pathogens. The direction of the CO2-mediated effects on SA- and JA-mediated defenses varies between reported studies, suggesting that the defense output is influenced by environmental context. These findings highlight that a wider dynamic range of climate change parameters should be studied simultaneously to harness plant traits for the development of future climate-resilient crops.
Highlights
Climate change due to increasing CO2 levels in the Earth’s atmosphere may affect interactions between plants and their attackers resulting in significant effects on crop yields in agriculture
To investigate whether the activity of the jasmonic acid (JA) or salicylic acid (SA) pathways is altered under different atmospheric CO2 conditions in Arabidopsis plants, we analyzed the expression of genes that are responsive to these two hormones in plants that had grown at three atmospheric CO2 concentrations
The FLG22-INDUCED RECEPTOR-LIKE KINASE1 (FRK1) gene was higher expressed at low atmospheric CO2 levels (Fig. 1c) and ISOCHORISMATE SYNTHASE1 (ICS1) expression was reduced under the high CO2 condition (Fig. 1d)
Summary
Climate change due to increasing CO2 levels in the Earth’s atmosphere may affect interactions between plants and their attackers resulting in significant effects on crop yields in agriculture. Plants are exposed to a wide array of pathogenic microbes. It is only since one and a half centuries that microbes have been recognized as causal agents of plant diseases. Plant pathogens are typically distinguished by their infection strategy. To defend themselves against pathogenic invaders, plants have developed a sophisticated defense system that recognizes pathogen-associated molecules and subsequently activate downstream defense cascades. The mutually antagonistic phytohormones salicylic acid (SA) and jasmonic acid (JA) are crucial for the regulation of the plant immune signaling network (Pieterse et al 2009), in which the SA pathway typically regulates defenses against biotrophic pathogens, whereas JA is effective against necrotrophic pathogens and insect herbivores
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