Synthesis of novel N-(2-phenyl-3-pyridyl) thiadiazole/isothiazole carboxamide analogs as potent plant elicitors

BACKGROUND Plant elicitors are a class of plant protection agents that can stimulate plant immunity against phytopathogen without a potential resistance problem. In searching for novel plant elicitor candidates, a series of novel N-(2-phenyl-3-pyridyl) thiadiazole/isothiazole carboxamide analogs were designed and synthesized. RESULTS In vitro bioassay showed that all new compounds exhibited weak direct fungicidal activity. However, compounds 3b, 3g, 3n and 3o showed broad spectrum of in vivo activity against four plant fungi tested. In particularly, 3g showed 80% activity against Rhizoctonia solani in a glasshouse at a concentration of 1 mu g mL(-1). For induction activity of tobacco against tobacco mosaic virus (TMV), compounds 3c and 3v showed 67% and 68% inhibitory activity, respectively, which were superior to the positive controls ribavirin and ningnanmycin. Compound 3g showed moderate induction activity (41%). Reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis found that, 3g could up-regulate expression of genes that are related to reactive oxygen species (ROS), pathogenesis-related protein (PRP) and salicylic acid (SA) signalling. CONCLUSION These results indicated that 3g as an elicitor candidate might act on the SA signalling pathway. According to our findings, N-(2-phenyl-3-pyridyl) thiadiazole/isothiazole carboxamide analogs might be promising lead scaffolds as a novel plant elicitor for further investigation.

Automated summary

The plant elicitor candidate 3g was found to potentially act on the salicylic acid signaling pathway, as evidenced by up-regulation of genes related to reactive oxygen species, pathogenesis-related protein, and salicylic acid signaling. N-(2-phenyl-3-pyridyl) thiadiazole/isothiazole carboxamide analogs may serve as promising lead scaffolds for further investigation as novel plant elicitors.