A prophage‐encoded effector from “Candidatus Liberibacter asiaticus” targets ASCORBATE PEROXIDASE6 in citrus to facilitate bacterial infection

Citrus huanglongbing (HLB), associated with the unculturable phloem-limited bacterium "Candidatus Liberibacter asiaticus" (CLas), is the most devastating disease in the citrus industry worldwide. However, the pathogenicity of CLas remains poorly understood. In this study, we show that AGH17488, a secreted protein encoded by the prophage region of the CLas genome, suppresses plant immunity via targeting the host ASCORBATE PEROXIDASE6 (APX6) protein in Nicotiana benthamiana and Citrus sinensis. The transient expression of AGH17488 reduced the chloroplast localization of APX6 and its enzyme activity, inhibited the accumulation of reactive oxygen species (H2 O2 and O2- ) and the lipid oxidation endproduct malondialdehyde in plants, and promoted the proliferation of Pseudomonas syringae pv. tomato DC3000 and Xanthomonas citri subsp. citri. This study reveals a novel mechanism underlying how CLas uses a prophage-encoded effector, AGH17488, to target a reactive oxygen species accumulation-related gene, APX6, in the host to facilitate its infection.