The antitoxin EndoAI is a TA system component that directly inhibits EndoA activity in vitro. The targeted activation of a TA system represents a potentially novel antimicrobial or antiviral strategy. However, whether the antitoxin functions alone and can induce plant disease resistance remain unknown. An endoAI was previously identified in the genome of Paenibacillus terrae NK3-4. It underwent a bioinformatics analysis, cloned and expressed in Escherichia coli. Then the functions of EndoAI inducing plant resistance to diseases as an elicitor were evaluated. The results showed that, EndoAI is a stable, alkaline, and hydrophilic protein, with a J-shaped three-dimensional structure in the absence of a ligand. It was clustered on the same branch with an antitoxin from Paenibacillus polymyxa SC2. Ectopically expressed EndoAI triggered a reactive oxygen species burst and a positive hypersensitive response (HR) in tobacco leaves. Moreover, 2 μmol EndoAI induced HR activity in tomato leaf, and it remained active after a 15-min exposure at 4–50 °C, and pH 6–8. Additionally, EndoAI induced plant systemic resistance against Alternaria alternata and tobacco mosaic virus, and the up-regulated transcription of PR genes, including PR1a, PR1b, PR5, PDF1.2, COL1, NPR1, and PAL. These results imply that EndoAI may enhance the disease resistance of tobacco by promoting a series of early defense responses and up-regulating PR gene expression. These findings are relevant for future investigations on the mechanism underlying the EndoAI–plant interaction that leads to enhanced disease resistance. Furthermore, the endoAI may be useful for developing effective biocontrol agents to protect plants from diseases.

中文翻译：

---

抗毒素 EndoAI 作为蛋白质诱导剂可诱导烟草抗病性

抗毒素 EndoAI 是一种 TA 系统组件，可在体外直接抑制 EndoA 活性。TA 系统的靶向激活代表了一种潜在的新型抗菌或抗病毒策略。然而，抗毒素是否单独起作用并能诱导植物抗病性仍然未知。先前在土芽孢杆菌 NK3-4 的基因组中发现了一种内源 AI。它经过生物信息学分析，在大肠杆菌中克隆和表达。然后评估了 EndoAI 作为诱导物诱导植物抗病性的功能。结果表明，EndoAI是一种稳定的、碱性的、亲水的蛋白质，在没有配体的情况下呈J形三维结构。它与来自多粘类芽孢杆菌 SC2 的抗毒素聚集在同一分支上。异位表达的 EndoAI 触发了烟叶中活性氧的爆发和阳性超敏反应 (HR)。此外，2 μmol EndoAI 在番茄叶中诱导 HR 活性，并且在 4–50 °C 和 pH 6–8 下暴露 15 分钟后仍保持活性。此外，EndoAI 诱导植物对链格孢和烟草花叶病毒的系统抗性，并上调 PR 基因的转录，包括 PR1a、PR1b、PR5、PDF1.2、COL1、NPR1 和 PAL。这些结果意味着 EndoAI 可能通过促进一系列早期防御反应和上调 PR 基因表达来增强烟草的抗病性。这些发现与未来对 EndoAI 与植物相互作用导致抗病性增强的机制的研究有关。此外，