Elevated CO2 increases the abundance of the peach aphid on Arabidopsis by reducing jasmonic acid defenses.

Rising atmospheric CO2 concentrations can affect the induced defense of plants against herbivory by chewing insects, but little is known about whether elevated CO2 can change the inducible defense of plants against herbivory by aphids, which are phloem-sucking rather than tissue-chewing insects. Interactions between the green peach aphid Myzus persicae and four isogenic Arabidopsis thaliana genotypes including wild type and three induced defense pathway deficient mutants were examined under ambient and elevated CO2. Our data showed that elevated CO2 increased the population abundance of peach aphid when reared on wild type and SA-deficient mutant plants. Regardless of aphid infestation, elevated CO2 decreased the jasmonic acid (JA) but increased the salicylic acid (SA) level in wild-type plants. In addition, elevated CO2 increased SA level in SA-deficient mutant while did not change the JA level in JA-deficient mutant. Pathway enrichment analysis based on high-throughput transcriptome sequencing suggested that CO2 level, aphid infestation, and their interactions (respectively) altered plant defense pathways. Furthermore, qPCR results showed that elevated CO2 up-regulated the expression of SA-dependent defense genes but down-regulated the expression of JA/ethylene-dependent defense genes in wild-type plants infested by aphids. The current study indicated that elevated CO2 tended to enhance the ineffective defense-SA signaling pathway and to reduce the effective defense-JA signaling pathway against aphids, which resulted in increased aphid numbers. Crown