Alpha-momorcharin, a RIP produced by bitter melon, enhances defense response in tobacco plants against diverse plant viruses and shows antifungal activity in vitro

Alpha-momorcharin (alpha-MMC) is type-1 ribosome inactivating proteins (RIPs) with molecular weight of 29 kDa and has lots of biological activity. Our recent study indicated that the alpha-MMC purified from seeds of Momordica charantia exhibited distinct antiviral and antifungal activity. Tobacco plants pre-treated with 0.5 mg/mL alpha-MMC 3 days before inoculation with various viruses showed less-severe symptom and less reactive oxygen species (ROS) accumulation compared to that inoculated with viruses only. Quantitative real-time PCR analysis revealed that the replication levels of viruses were lower in the plants treated with the alpha-MMC than control plants at 15 days post inoculation. Moreover, the coat protein expression of viruses was almost completely inhibited in plants which were treated with the alpha-MMC compared with control plants. Furthermore, the SA-responsive defense-related genes including non-expressor of pathogenesis-related genes 1 (NPR1), PR1, PR2 were up-regulated and activities of some antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) were increased after the alpha-MMC treatment. In addition, the alpha-MMC (500 mu g/mL) revealed remarkable antifungal effect against phytopathogenic fungi, in the growth inhibition range 50.35-67.21 %, along with their MIC values ranging from 100 to 500 mu g/mL. The alpha-MMC had also a strong detrimental effect on spore germination of all the tested plant pathogens along with concentration as well as time-dependent kinetic inhibition of Sclerotinia sclerotiorum. The alpha-MMC showed a remarkable antiviral and antifungal effect and hence could possibly be exploited in crop protection for controlling certain important plant diseases.