Antitoxin EndoAI can induce disease resistance in tobacco as a protein elicitor

Abstract

Abstract Background 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. Results 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. Conclusions 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. Graphical Abstract