BDP-30, a systemic resistance inducer from Boerhaavia diffusa L., suppresses TMV infection, and displays homology with ribosome-inactivating proteins

Root extract of Boerhaavia diffusa L. induced systemic resistance in tobacco against Tobacco mosaic virus. A 30 kDa protein was isolated as the active component, called BDP-30 on the basis of the molecular weight and source plant. BDP-30, a glycoprotein, was found to be temperature and protease resistant. It was basic, possessing a pI greater than 9.0. In-gel proteolytic digestion of BDP-30 generated two peptides that possessed the amino acid sequence KLYDIPPLR and KVTLPYSGNYER by LC/MS/MS. Both peptides shared absolute sequence identity with trichosanthin, a ribosome-inactivating protein from Trichosanthes kirilowii, and a 78% and 100% homology respectively with an RIP from Bryonia dioica, bryodin. Further, effort was made to look at the fate of TMV in induced resistant Nicotiana tabacum cv. Xanthi, a systemic host of the virus, at specified days after inoculation in control and treated plants. TMV coat protein (CP) was detected by immunoblot 7 days post inoculation up to 21 days in the control set, but not in treated resistant plants. TMV RNA was detected by RT-PCR using TMV-CP specific primers. Resistant tobacco did not show presence of TMV RNA up to 21 days of inoculation. This suggests that BDP-30 may be suppressing TMV replication.