Abstract
Citrus huanglongbing (HLB), associated with the unculturable phloem‐limited bacterium “
Candidatus
Liberibacter asiaticus” (
C
Las), is the most devastating disease in the citrus industry worldwide. However, the pathogenicity of
C
Las remains poorly understood. In this study, we show that AGH17488, a secreted protein encoded by the prophage region of the
C
Las 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 (H
2
O
2
and O
2
−
) 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
C
Las uses a prophage‐encoded effector, AGH17488, to target a reactive oxygen species accumulation‐related gene,
APX6
, in the host to facilitate its infection.