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

doi:10.3389/fpls.2023.1224736

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

Front Plant Sci. 2023 Jul 24:14:1224736. doi: 10.3389/fpls.2023.1224736. eCollection 2023.

Authors

Shushe Zhang^{1

2}, Xuefeng Wang¹, Jun He¹, Song Zhang³, Tingchang Zhao², Shimin Fu¹, Changyong Zhou¹

Affiliations

¹ Citrus Research Institute, Southwest University/National Citrus Engineering Research Center, Chongqing, China.
² State Key Laboratory for Biology of Plant Diseases and Insect Pests, Chinese Academy of Agriculture Sciences, Institute of Plant Protection, Beijing, China.
³ Guangxi Citrus Breeding and Cultivation Engineering Technology Center Academy of Specialty Crops, Guangxi, Guilin, China.

Abstract

Citrus Huanglongbing (HLB) is the most destructive citrus disease worldwide, mainly caused by 'Candidatus Liberibacter asiaticus' (CLas). 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 (CLas4425), 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 CLas infected psyllids, CLas4425 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 ΔhopQ1-1 and CLas, respectively. Furthermore, the salicylic acid (SA) level along with the expression of genes NPR1/EDS1/NDR1/PRs in SA signal transduction was repressed in CLas4425 transgenic citrus plants. Taken together, CLas4425 is a virulence factor that promotes CLas proliferation, likely by interfering with SA-mediated plant immunity. The results obtained facilitate our understanding of CLas pathogenesis.

Keywords: CLas; CLas4425; Citrus Huanglongbing (HLB); cell death; effector; virulence factor.

Grants and funding

This research was partially supported by the National Key R&D Program of China (2021YFD1400800), the National Natural Sciences Foundation of China (31871925), and the Natural Sciences Foundation of Chongqing (cstc2020jcyj-msxmX1036).