Prophage-Encoded Peroxidase in 'Candidatus Liberibacter asiaticus' Is a Secreted Effector That Suppresses Plant Defenses
Prophage-Encoded Peroxidase in 'Candidatus Liberibacter asiaticus' Is a Secreted Effector That Suppresses Plant Defenses
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DOI：
10.1094/mpmi-07-15-0145-r
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发表时间：
2015-12-01
影响因子：
3.5
通讯作者：
Gabriel, Dean W.
中科院分区：
文献类型：
--
作者：
Jain, Mukesh;Fleites, Laura A.;Gabriel, Dean W.
柑桔黄龙病是柑桔上的一种致死性病害，由木虱传播，引起柑桔黄龙病。致病性最强的。L. asiaticus的菌株携带两个几乎相同的前噬菌体，与菌株UF 506中的SC 1和SC 2相似。观察到SC2作为编码活性氧清除过氧化物酶（SC2_gp095）（一种预测的溶原性转换因子）的中等高拷贝切除质粒复制。SC2_gp095在长春花中的表达水平显著高于柑橘，在木虱中受到抑制。将SC2_gp095克隆到穿梭载体中，并转化到大肠杆菌和新月形韧皮部杆菌（Liberibacter crescens）中，所述新月形韧皮部杆菌是'Ca. L.亚洲人。转化湖Crescens细胞在琼脂平板上显示出20 - 25%的增强的对11202的抗性，47%的更高的酶活性，以及在液体培养物中的增强的生长。预测了SC2_gp095和L. crescens通过酶和Western印迹分析确认。SC2_gp095在植物中的瞬时表达导致RbohB的强烈转录下调，RbohB是植物中H2 O2介导的防御信号传导的关键守门人，这有助于解释在'Ca. L.亚洲种感染的柑橘卡L. asiaticus的过氧化物酶可能是一种分泌的、水平获得的效应物，其抑制宿主症状的发展，这是大多数生物营养型植物病原体使用的策略。
'Candidatus Liberibacter asiaticus' is transmitted by psyllids and causes huanglongbing (HLB), a lethal disease of citrus. Most pathogenic 'Ca. L. asiaticus' strains carry two nearly identical prophages similar to SC1 and SC2 in strain UF506. SC2 was observed to replicate as a moderately high-copy excision plasmid encoding a reactive oxygen species scavenging peroxidase (SC2_gp095), a predicted lysogenic conversion factor. SC2_gp095 was expressed at significantly higher levels in periwinkle than in citrus and was suppressed in psyllids. SC2_gp095 was cloned in a shuttle vector and transformed into Escherichia colt and Liberibacter crescens, a culturable proxy for 'Ca. L. asiaticus'. Transformed L. crescens cells showed 20 to 25% enhanced resistance to 11202 on agar plates, 47% greater enzymatic activity, and enhanced growth in liquid cultures. A nonclassical secretion potential was predicted for SC2_gp095 and secretion from L. crescens was confirmed by enzymatic and Western blot analyses. Transient expression of SC2_gp095 in planta resulted in strong transcriptional downregulation of RbohB, the key gatekeeper of the H2O2-mediated defense signaling in plants, helping explain the surprisingly long incubation period (years) before HLB symptoms appear in 'Ca. L. asiaticus' infected citrus. 'Ca. L. asiaticus' peroxidase is likely a secreted, horizontally acquired effector that suppresses host symptom development, a tactic used by most biotrophic plant pathogens.