Groundnut bud necrosis virus (GBNV), a member of the genus Tospovirus, has an extensive host range and is associated with necrosis disease of chilli (Capsicum annuum L.), which is a major threat to commercial production. Plant growth promoting rhizobacteria (PGPR) have been investigated for their antiviral activity in several crops and for their potential use in viral disease management. However, the microbial mechanisms associated with PGPR in triggered immunity against plant viruses have rarely been studied. To understand the innate immune responses activated by Bacillus spp. against GBNV, we studied microbe-associated molecular pattern (MAMP) triggered immunity (MTI) in chilli using transient expression of the flagellin gene of Bacillus amyloliquefaciens CRN9 from Agrobacterium clones, which also induced the expression of EAS1 gene transcripts coding for epi-aristolochene synthase, which is responsible for the accumulation of capsidiol phytoalexin. In addition, the transcript levels of WRKY33 transcription factor and salicylic acid (SA)-responsive defense genes such as NPR1, PAL, PO and SAR8.2 were increased. Jasmonate (JA)-responsive genes, viz., PDF, and LOX genes, were also upregulated in chilli plants challenged with GBNV. Further analysis revealed significant induction of these genes in chilli plants treated with B. amyloliquefaciens CRN9 and benzothiadiazole (BTH). The transcript levels of defense response genes and pathogenesis-related proteins were significantly higher in plants treated with Bacillus and BTH and remained significantly higher at 72 h post-inoculation and compared to the inoculated control. The plants treated with flagellin using the agrodrench method and exogenous treatment with B. amyloliquefaciens and BTH showed resistance to GBNV upon mechanical inoculation and a reduced virus titre which was confirmed by qPCR assays. Thus, transient expression of flagellin, a MAMP molecule from B. amyloliquefaciens CRN9, is able to trigger innate immunity and restrain virus growth in chilli via induced systemic resistance (ISR) activated by both the SA and JA/ET signalling pathways.

中文翻译：

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解淀粉芽孢杆菌的鞭毛蛋白可作为辣椒（Capsicum annuum L.）花生芽坏死病毒的抗性诱导剂。

花生芽坏死病毒(GBNV)是Tospovirus属的一员，宿主范围广泛，与辣椒坏死病有关，是商业生产的主要威胁。人们已经研究了促进植物根际细菌（PGPR）在多种作物中的抗病毒活性及其在病毒性疾病管理中的潜在用途。然而，与 PGPR 触发植物病毒免疫相关的微生物机制却很少被研究。了解芽孢杆菌属激活的先天免疫反应。针对GBNV，我们利用农杆菌克隆中解淀粉芽孢杆菌CRN9的鞭毛蛋白基因的瞬时表达，研究了辣椒中微生物相关分子模式（MAMP）触发的免疫（MTI），该基因还诱导了编码表马兜铃烯合酶的EAS1基因转录本的表达，负责辣椒素植物抗毒素的积累。此外，WRKY33转录因子和水杨酸（SA）反应性防御基因（例如NPR1、PAL、PO和SAR8.2）的转录水平增加。茉莉酸 (JA) 响应基因，即 PDF 和 LOX 基因，在接受 GBNV 攻击的辣椒植物中也上调。进一步的分析表明，用解淀粉芽孢杆菌 CRN9 和苯并噻二唑 (BTH) 处理的辣椒植物中这些基因得到显着诱导。与接种对照相比，用芽孢杆菌和 BTH 处理的植物中防御反应基因和发病机制相关蛋白的转录水平显着较高，并且在接种后 72 小时仍显着较高。使用 agrodrench 方法用鞭毛蛋白处理以及用解淀粉芽孢杆菌和 BTH 进行外源处理的植物在机械接种后表现出对 GBNV 的抗性，并通过 qPCR 测定证实了病毒滴度降低。因此，鞭毛蛋白（来自解淀粉芽孢杆菌 CRN9 的 MAMP 分子）的瞬时表达能够触发先天免疫，并通过 SA 和 JA/ET 信号通路激活的诱导系统抗性 (ISR) 抑制辣椒中的病毒生长。