The dynamics of molecular components that regulate aphid-plant interactions
Aphids are economically important insect pests, which feed on phloem sap using stylets. Aphids cause significant losses of crop yield, through draining plant resources and vectoring over 275 plant viruses. In plant-pathogen interactions, basal plant defense involving pathogen associated molecular pattern (PAMP) triggered immunity (PTI) and effector triggered immunity (ETI) effectively fends off the majority of plant pathogens. I aimed to discover whether these mechanisms are also involved in the plant response to aphids. I found that elicitors present within aphids can evoke PTI/ETI defense responses. In Arabidopsis thaliana, perception of aphid elicitors requires the Leucine-Rich Repeat Receptor- Like Kinase (LRR-RLK) BAK1, which is required for multiple PTI responses via interaction with other RLKs. I identified two RLKs which may detect aphid elicitors and provide specificity to aphid detection. Successful aphid colonization of plants is thought to involve the suppression of PTI and ETI via effectors, leading to effector-triggered susceptibility (ETS). I investigated a Myzus persicae effector, Mp10, and found that it was required for success on Arabidopsis and could block immune signalling. A plant target for Mp10 was identified via a yeast twohybrid screen. Further investigations suggest that the Mp10 target has previously unknown roles in immune receptor trafficking. Mp10 induces ETI-like responses when expressed in plants, which I found were not dependent upon Mp10 effector action or salicylic acid. A yeast two-hybrid screen of candidate aphid effectors revealed interactions with plant resistance proteins, which may play a role in the aphid-plant interaction. Aphid effector proteins were also found to interact with each other, suggesting a role in the regulation of effector action and delivery into plants. Taken together, the research described in this thesis has elucidated the roles of PTI, ETS and ETI in insect-plant interactions and identified specific plant and aphid proteins that are involved in these.
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