Protein-protein and DNA-protein interactions mediate induction of defense genes by fruit extract of Azadirachta indica A. Juss. in Solanum lycopersicum L.

KEY MESSAGE: The present work demonstrates that induction of defense-related genes in tomato by neem extract was mediated by protein-protein and DNA-protein interactions. The induction of elicitor-mediated defense responses in plants is known, but the molecular mechanisms underlying its induction are not well studied. In the present study, third node leaf from the base of aseptically raised tomato plants was treated with aqueous fruit extracts of Azadirachta indica A. Juss. (neem). Samples were collected from the treated node at 24-h intervals for up to 96 h and analyzed for the gene expression of phenylalanine ammonia lyase (PAL), Peroxidase (POX) and Polyphenol Oxidase (PPO), β-actin (standard). Samples were collected from elicitor-induced node at 5-min interval up to 70 min for analysis of protein-protein and DNA-protein interactions. The results demonstrated the induction of expression of PAL, POX and PPO due to the treatment whereas no change was observed in the expression of β-actin. There was disappearance of lower molecular weight proteins which cross-linked with other proteins to form complexes. MALDI-TOF MS analysis revealed the interaction of mitogen-activated protein kinases (MAPK). The analysis of proteins interacted with DNA after induction by neem extract indicated the involvement of WRKY transcriptional factors. Neem-elicited defense responses could possibly due to interaction of proteins with other proteins and transcription factors with DNA which might be crucial in enhancing the expression of defense-related genes (PAL, POX and PPO).