Effectors from a Bacterial Vector-Borne Pathogen Exhibit Diverse Subcellular Localization, Expression Profiles and Manipulation of Plant Defense.

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Climate change is predicted to increase the prevalence of vector-borne disease due to expansion of insect populations. Candidatus Liberibacter solanacearum (CLso) is a phloem-limited pathogen associated with multiple economically important diseases in Solanaceous crops. Little is known about the strategies and pathogenicity factors CL so uses to colonize its vector and host. We determined the CLso effector repertoire by predicting SEC secreted proteins across four different CLso haplotypes, investigated effector localization in planta, and profiled effector expression in the vector and host. The localization of CLso effectors in Nicotiana revealed diverse eukaryotic subcellular targets. The majority of tested effectors were unable to suppress plant immune responses, indicating they possess unique activities. Expression profiling in tomato and the psyllid Bactericera cockerelli indicated CLso differentially interacts with its host and vector and can switch effector expression in response to these environments. This study reveals CLso effectors possess complex expression patterns, target diverse host organelles and the majority are unable to suppress host immune responses. A mechanistic understanding of CLso effector function will reveal novel targets and provide insight into phloem biology.