A Sec-dependent effector, CLIBASIA_04425, contributes to virulence in ‘Candidatus Liberibater asiaticus’
Shushe Zhang, Xuefeng Wang, Jun He, Song Zhang, Tingchang Zhao, Shimin Fu, Changyong Zhou
Abstract
Citrus Huanglongbing (HLB) is the most destructive citrus disease worldwide, mainly caused by ‘ Candidatus Liberibacter asiaticus’ ( C 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 Nicotiana benthamiana , CLIBASIA_04425 ( C Las4425), was identified. Of particular interest, its cell death-inducing activity is associated with its subcellular localization and the cytoplasmic receptor Botrytis -induced kinase 1 (BIK1). Compared with C Las infected psyllids, C Las4425 showed higher expression level in planta. The transient expression of CLas4425 in N . benthamiana and its overexpression in Citrus sinensis enhanced plant susceptibility to Pseudomonas syringae pv. tomato DC3000 Δ hopQ1-1 and C Las, respectively. Furthermore, the salicylic acid (SA) level along with the expression of genes NPR1 / EDS1 / NDR1 / PR s in SA signal transduction was repressed in C Las4425 transgenic citrus plants. Taken together, C Las4425 is a virulence factor that promotes C Las proliferation, likely by interfering with SA-mediated plant immunity. The results obtained facilitate our understanding of C Las pathogenesis.