Effector
<scp>
C
Las0185
</scp>
targets methionine sulphoxide reductase
<scp>B1</scp>
of
Citrus sinensis
to promote multiplication of ‘
Candidatus
Liberibacter asiaticus’ via enhancing enzymatic activity of ascorbate peroxidase 1
Abstract
Citrus huanglongbing (HLB) has been causing enormous damage to the global citrus industry. As the main causal agent, ‘
Candidatus
Liberibacter asiaticus’ (
C
Las) delivers a set of effectors to modulate host responses, while the modes of action adopted remain largely unclear. Here, we demonstrated that CLIBASIA_00185 (
C
Las0185) could attenuate reactive oxygen species (ROS)‐mediated cell death in
Nicotiana benthamiana
. Transgenic expression of
C
Las0185 in
Citrus sinensis
‘Wanjincheng’ enhanced plant susceptibility to
C
Las. We found that methionine sulphoxide reductase B1 (CsMsrB1) was targeted by the effector, and its abundance was elevated in
CLas0185
‐transgenic citrus plants. Their interaction promoted
C
Las proliferation. We then determined that CsMsrB1 sustained redox state and enzymatic activity of ascorbate peroxidase 1 (CsAPX1) under oxidative stress. The latter reduced H
2
O
2
accumulation and was associated with host susceptibility to
C
Las infection. Consistently, citrus plants expressing
C
Las0185 and CsMsrB1 conferred enhanced APX activity and decreased H
2
O
2
content. Taken together, these findings revealed how
C
Las0185 benefits
C
Las colonization by targeting CsMsrB1, which facilitated the antioxidant activity and depressed ROS during pathogen infection.