A Sec-dependent effector, CLIBASIA_04425, contributes to virulence in ' Liberibater asiaticus'.

Citrus Huanglongbing (HLB) is the most destructive citrus disease worldwide, mainly caused by ' Liberibacter asiaticus' (Las). It encodes a large number of Sec-dependent effectors that contribute to HLB progression. In this study, an elicitor triggering ROS burst and cell death in , CLIBASIA_04425 (Las4425), was identified. Of particular interest, its cell death-inducing activity is associated with its subcellular localization and the cytoplasmic receptor -induced kinase 1 (BIK1). Compared with Las infected psyllids, Las4425 showed higher expression level in planta. The transient expression of in . and its overexpression in enhanced plant susceptibility to pv. DC3000 Δ and Las, respectively. Furthermore, the salicylic acid (SA) level along with the expression of genes ///s in SA signal transduction was repressed in Las4425 transgenic citrus plants. Taken together, Las4425 is a virulence factor that promotes Las proliferation, likely by interfering with SA-mediated plant immunity. The results obtained facilitate our understanding of Las pathogenesis.