Aphid, a specialized phloem sap-feeding insect, is one of the major pests of a number of economic important crops, including soybean, cotton, and maize. Aphid can have devastating effects on the crop production by limiting plant growth, as well as serving as vectors for disease. Therefore, research on identification of plant resistance mechanisms to aphid is important for crop improvement. Here, I have developed a system consisting of Arabidopsis thaliana and green peach aphids (Myzus persicae) to study plant-aphid interaction. In my research project, the role of BIK1 was investigated in Arabidopsis infested with the green peach aphid. Loss of BIK1 function adversely impacted aphid settling, feeding and reproduction. Relative to wild-type plants, bik1 displayed higher aphid-induced H2O2 accumulation and more severe lesions, resembling a hypersensitive response (HR) against pathogens. Basal as well as induced salicylic acid and ethylene accumulation were in in the bik1 mutant. Intriguingly, elevated salicylic acid levels did not contribute to the HR-like symptoms or to the heightened aphid resistance associated with the bik1 mutant. Elevated ethylene levels in bik1 accounted for an initial, short-term repellence. Introducing a loss-of-function mutation in the aphid resistance and senescence-promoting gene PHYTOALEXIN DEFICIENT4 (PAD4) into the bik1 background blocked both aphid resistance and HR-like symptoms, indicating bik1-mediated resistance to aphids is PAD4-dependent. Taken together, Arabidopsis BIK1 confers susceptibility to aphid infestation through its suppression of PAD4 expression. Furthermore, the results underscore the role of ROS and cell death in plant defense against phloem sap-feeding insects.
