Effect of elevated CO2 and O3 on phytohormone-mediated plant resistance to vector insects and insect-borne plant viruses

Climatic variations are becoming important limiting factors for agriculture productivity, as they not only directly affect the plant net primary productivity but can also modulate the outbreak of plant diseases and pests. Elevated CO2 and O3 are two important climatic factors that have been widely studied before. Elevated CO2 or O3 alters the host plant physiology and affects the vector insects and plant viruses via bottom-up effects of the host plants. Many studies have shown that elevated CO2 or O3 decreases the plant nitrogen content, which modulates the characteristics of vector insects. Recent evidence also reveals that hormone-dependent signaling pathways play a critical role in regulating the response of insects and plant viruses to elevated CO2 or O3. In the current review, we describe how elevated CO2 or O3 affects the vector insects and plant viruses by altering the SA and JA signaling pathways. We also discuss how changes in the feeding behavior of vector insects or the occurrence of plant viruses affects the interactions between vector insects and plant viruses under elevated CO2 or O3. We suggest that new insights into the upstream network that regulates hormone signaling and top-down effects of natural enemies would provide a comprehensive understanding of the complex interactions taking place under elevated CO2 or O3.