SYSTEMIC ANTIVIRAL RESISTANCE INDUCED IN PAPAYA BY CAP34 A RESISTANCE INDUCING PROTEIN FROM CLERODENDRUM ACULEATUM IS ASSOCIATED WITH A PROTEINACEOUS VIRUS INHIBITORY ACTIVITY
A. Srivastava, S. Srivastava, V. Prasad
Proteins from non-host higher plants are known to induce systemic resistance in plants against virus infections in susceptible plants. CAP-34 is one such known protein with molecular mass 34 kDa, isolated from Clerodendrum aculeatum. CAP-34 was also shown to be acting against Papaya ringspot virus (PRSV) in papaya by imposing a possible check on PRSV replication. Since the induced resistance was systemic, efforts were made to identify host components that could be involved in it. In the process, a virus inhibitory activity was observed concomitantly with the development of resistance. This paper reports the time- course of the virus inhibitory activity and purification to electrophoretic homogeneity of a proteinaceous virus inhibitory agent (VIA), and the determination of some of its biochemical characteristics. This VIA, denoted CP-VIA-34 based on the host where it came from (Carica papaya), and was determined to be a basic protein that inactivated Tobacco mosaic virus (TMV) ex vivo when bioassayed on Nicotiana tabacum cv Samsun NN. CP-VIA-34 had a molecular mass of 34 kDa, was thermostable and resistant to proteinase K. It did not exhibit protease (tested separately on BSA, and purified TMV), DNase and RNase activities. The paper discusses the characteristics of the CP-VIA-34, and its relevance in relation to some other known plant defence proteins such as the ribosome-inactivating proteins, inhibitor of virus replication, antiviral factor, and the PR-proteins.