"Candidatus Liberibacter asiaticus" Secretes Nonclassically Secreted Proteins That Suppress Host Hypersensitive Cell Death and Induce Expression of Plant Pathogenesis-Related Proteins
"Candidatus Liberibacter asiaticus" Secretes Nonclassically Secreted Proteins That Suppress Host Hypersensitive Cell Death and Induce Expression of Plant Pathogenesis-Related Proteins
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DOI：
10.1128/aem.00019-21
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发表时间：
2021-04-01
影响因子：
4.4
通讯作者：
Li, Weimin
中科院分区：
文献类型：
--
作者：
Du, Peixiu;Zhang, Chao;Li, Weimin
虽然新出现的证据表明，细菌胞外出口许多细胞质蛋白被称为非经典分泌蛋白（ncSecPs）为自己的利益，在细胞外环境中的ncSecPs的机制和功能意义仍然难以捉摸。“亚洲柑桔黄龙病菌”（CLas）是一种引起黄龙病（HLB）的苛养革兰氏阴性细菌，黄龙病是全球最具破坏性的柑橘疾病。在这项研究中，使用SecretomeP程序加上大肠杆菌碱性磷酸酶测定，我们确定了27个ncSecPs从CLas基因组。此外，我们证明，其中10个表现出显着更高水平的基因表达在柑橘比木虱宿主，特别是抑制过敏反应（IR）为基础的细胞死亡和H2 O2的过度积累，在烟草本塞姆亚纳，表明其对早期植物防御相反的影响。然而，这些蛋白质也显着增强了病程相关蛋白1（PR-1），PR 2和PR-5，植物防御机制的重要组成部分的基因表达。另外的实验揭示了这些PR基因，特别是PR-1和PR-5的表达增加，可以负调节基于HR的细胞死亡发展和H2 O2积累。值得注意的是，CLas感染清楚地诱导PR-1，PR-2，和PR-5的基因表达在两个HLB耐受和HLB敏感的柑橘植物物种。考虑到这些数据，我们假设，CLas已经演变成一个阿森纳的ncSecPs的功能合作压倒早期植物防御诱导宿主PR genes.IMPORTANCE在这项研究中，我们提出了一个相结合的计算和实验方法，允许一个快速和有效的识别ncSecPs从细菌，特别是不可培养的细菌，如CLas。同时，该研究确定了许多CLas ncSecPs抑制基于HR的细胞死亡，从而表明细菌ncSecPs在细胞外环境中的新作用。更重要的是，发现这些ncSecPs可能通过利用宿主PR蛋白来抑制细胞死亡。这些数据为理解CLas的发病机制提供了新的线索，也提出了植物病原体操纵宿主细胞机制以建立感染的新途径。
Although emerging evidence indicates that bacteria extracellularly export many cytoplasmic proteins referred to as nonclassically secreted proteins (ncSecPs) for their own benefit, the mechanisms and functional significance of the ncSecPs in the extracellular milieu remain elusive. "Candidatus Liberibacter asiaticus" (CLas) is a fastidious Gram-negative bacterium that causes Huanglongbing (HLB), the most devastating citrus disease globally. In this study, using the SecretomeP program coupled with an Escherichia coli alkaline phosphatase assay, we identified 27 ncSecPs from the CLas genome. Further, we demonstrated that 10 of these exhibited significantly higher levels of gene expression in citrus than in psyllid hosts and particularly suppressed hypersensitive response (I-IR)-based cell death and H2O2 overaccumulation in Nicotiana benthamiana, indicating their opposing effects on early plant defenses. However, these proteins also dramatically enhanced the gene expression of pathogenesis-related 1 protein (PR-1), PR2, and PR-5, essential components of plant defense mechanisms. Additional experiments disclosed that the increased expression of these PR genes, in particular PR-1 and PR-5, could negatively regulate HR-based cell death development and H2O2 accumulation. Remarkably, CLas infection clearly induced gene expression of PR-1, PR-2, and PR-5 in both HLB-tolerant and HLB-susceptible species of citrus plants. Taking together these data, we hypothesized that CLas has evolved an arsenal of ncSecPs that function cooperatively to overwhelm the early plant defenses by inducing host PR genes.IMPORTANCE In this study, we present a combined computational and experimental methodology that allows a rapid and efficient identification of the ncSecPs from bacteria, in particular unculturable bacteria like CLas. Meanwhile, the study determined that a number of CLas ncSecPs suppressed HR-based cell death and thus indicated a novel role for the bacterial ncSecPs in the extracellular milieu. More importantly, these ncSecPs were found to suppress cell death presumably by utilizing host PR proteins. The data overall provide a novel clue to understand the CLas pathogenesis and also suggest a new way by which phytopathogens manipulate host cellular machinery to establish infection.