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An effector from 'Candidatus Liberibacter asiaticus' targets the armadillo (ARM) repeated protein of Citrus sinensis to inhibit salicylic acid-mediated host immunity

Yalin Mei1, 2*, Zaiyu Yang1, 2*, Shushe Zhang1, 2, Pan Shen1, 3, Changyong Zhou1, 2, Xuefeng Wang1, 2#

Integrative Science Center of Germplasm Creation in Western China (CHONGQING) Science City, Citrus Research Institute, Southwest University, Chongqing 400712, China

National Citrus Engineering Research Center, Citrus Research Institute, Southwest University, Chongqing 400712, China

College of food and Biology, Jingchu University of Technology, Jingmen 448000, China

 Highlights 

1.CsARM26 subsequently degrades CLas0185 through the 26S proteasome pathway but exhibits minimal impact on CLas0185 pathogenicity.

2.CsARM26 citrus plants suppressed the accumulation of free salicylic acid (SA) and the expression of SA-associated genes.

3.An ARM repeated protein plays a role in the immune response to the CLas–citrus interaction, establishing a foundation for further investigation of the molecular mechanisms of CLas infection.

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摘要  

柑橘黄龙病(HLB)已对全球柑橘产业造成了广泛损害。黄龙病传播范围广,尚无有效药物根治黄龙病,黄龙病的主要病原体亚洲韧皮部杆菌CLas)利用效应子来调节宿主的防御反应,但这些效应子的作用机制仍不清楚。本研究前期发现,柑橘转基因CLas0185能够促进HLB侵染,酵母双杂筛库发现潜在互作蛋白CsARM26, 并进一步利用利用酵母双杂 (Y2H)、烟草双分子荧光(BiFC)以及免疫共沉淀(Co-IP)技术证明,柑橘重复蛋白 CsARM26 在体内和体外均与 CLIBASIA_00185CLas0185)相互作用。为探究两者互作分子机制,在本氏烟草中瞬时共表达CLas0185CsARM26,利用蛋蛋白免疫印迹(WB)技术检测发现CLas0185 增加了 CsARM26 的丰度,而 CsARM26 能促进CLas蛋白降解。进一步发现,CsAMR26并不具有E3连接酶活性,表明CsARM26可能通过与相关E3连接酶互作促进CLas0185降解。此外,CLas0185 CsARM26 的瞬时共表达促进了柑橘黄溃疡病的侵染。转基因 CsARM26 柑橘植株抑制了游离水杨酸(SA)的积累以及与 SA 相关基因的表达,CsARM26转录组数据表明免疫相关基因显著下调,以及水杨酸相关通路受到显著影响。本研究结果表明,CsARM26蛋白参与了柑橘对 CLas 互作的免疫反应,为 CLas 感染的分子机制进一步研究提供了基础。



Abstract  

Citrus Huanglongbing (HLB) has caused extensive damage to the global citrus industry. 'Candidatus Liberibacter asiaticus' (CLas), the primary causal agent of HLB, utilizes effectors to modulate host defense responses, though the mechanisms of these effectors remain unclear. This study demonstrates that the Citrus ARM repeated protein CsARM26 interacted with CLIBASIA_00185 (CLas0185) in vivo and in vitro. CLas0185 enhanced the abundance of CsARM26, while CsARM26 destabilized the effector. Additionally, the transient co-expression of CLas0185 and CsARM26 facilitated infection by Xanthomonas citri subsp. citri. Moreover, transgenic CsARM26 citrus plants suppressed the accumulation of free salicylic acid (SA) and the expression of SA-associated genes. This study reveals that an ARM repeated protein plays a role in the immune response to the CLas–citrus interaction, establishing a foundation for further investigation of the molecular mechanisms of CLas infection.

Keywords:  Keywords: Huanglongbing, effector, SA, CsARM26  
Online: 15 November 2025  
Fund: 

This work was supported by the National Natural Sciences Foundation of China (U23A20196), National Key Research and Development Program of China (2021YFD1400800), Special Fund for Youth Team of Southwest University (SWU-XJLJ202310) and Innovation Research 2035 Pilot Plan of Southwest University (SWU-5331000008), Southwest University research and innovation project (SWUB 25096), Southwest University research and innovation project (SWUS24208).

About author:  #Correspondence Xuefeng Wang, E-mail: wangxuefeng@cric.cn; Yalin Mei, E-mail: 13872147844@163.com

Cite this article: 

Yalin Mei, Zaiyu Yang, Shushe Zhang, Pan Shen, Changyong Zhou, Xuefeng Wang. 2025. An effector from 'Candidatus Liberibacter asiaticus' targets the armadillo (ARM) repeated protein of Citrus sinensis to inhibit salicylic acid-mediated host immunity. Journal of Integrative Agriculture, Doi:10.1016/j.jia.2025.11.024

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