Song_2022_Ecotoxicol.Environ.Saf_248_114296

Elevated atmospheric carbon dioxide (eCO(2)) concentrations can alter the carbon:nitrogen ratio and palatability of host plants for herbivorous insects, but rhizobacteria likely mitigate the alteration and influence physiological adaptation of insects. In this study, we conducted transcriptomic analysis of maize (Zea mays) response to Azotobacter chroococcum (AC) inoculation under eCO(2) conditions in contrast to ambient CO(2) (aCO(2)), and studied the effects of plant-defense change of maize under eCO(2) on the oriental armyworm, Mythimna separata. Results showed that there were 16, 14, 16 and 135 differentially expressed genes that were associated with plant-defense response in maize leaves between aCO(2)-CK and aCO(2)-AC, eCO(2)-CK and eCO(2)-AC, aCO(2)-CK and eCO(2)-CK, aCO(2)-AC and eCO(2)-AC, respectively. Moreover, A. chroococcum inoculation and eCO(2) influenced plant hormone signal transduction of maize. Interestingly, A. chroococcum inoculation significantly decreased the contents of JA (jasmonic acid) and JA-Ile (isoleucine conjugate of JA) in leaves, but eCO(2) markedly increased contents of JA-Ile, JA and SA (salicylic acid). Compared to aCO(2), eCO(2) significantly decreased activity of protective enzyme (catalase), and increased activities of digestive (lipase and protease), protective (peroxidase) and detoxifying enzymes (carboxylesterase, Mixed-functional oxidase and glutathione s-transferase), prolonged developmental time, and decreased survival rate and body weight of larvae (P<0.05). A. chroococcum inoculation significantly increased the activity of protective enzyme (catalase), and decreased the activities of detoxifying enzymes (carboxylesterase, glutathione s-transferase and mixed-functional oxidase), thus increased the growth rate and body weight of larvae in comparison with no-inoculation of A. chroococcum (P<0.05). The indices of M. separata were significantly correlated with the foliar contents of JA, JA-Ile and SA (|r| = 0.44-0.85, P<0.05), indicating that A. chroococcum inoculation altered the physiological adaptation of M. separata under eCO(2) by disturbing defense substances in maize. Our results in understanding effects of A. chroococcum inoculation on maize resistance to herbivorous insects will be valuable for agricultural pest control in the future at eCO(2) conditions.