Pokeweed (Phytolacca americana L.) antiviral protein inhibits Zucchini yellow mosaic virus infection in a dose-dependent manner in squash plants

Abstract

Pokeweed antiviral protein (PAP) of Phytolacca americana L. (pokeweed) is a single-chain ribosome-inactivating protein(RIP) characterized by its ability to depurinate plant ribosomes. Here, we isolated, cloned, and expressed the ribosome inactivatingprotein (RIP) gene, designated as pokeweed antiviral protein type 1 (PAP I), from the summer leaves of pokeweed collected fromthe Black Sea region (Turkey). Our findings presented here provide direct evidence that exogenous application of PAP I causesconcentration-dependent inhibition of Zucchini yellow mosaic virus (ZYMV) infection on squash plants. Squash plants were exposedto PAP I protein with and without DMSO for four consecutive days. Regular spraying of approximately 30 kDa recombinant PAP I at2 µg mL–1 concentration prevented treated plants from mechanical virus infection. PAP I showed antiviral activity in 9 plants out of 15inoculated plants. Remarkably, simultaneous application of PAP, DMSO, and ZYMV did not prevent virus infection, suggesting thatPAP did not have any effect on viral RNA. In the absence of ZYMV the purified peptide was not cytotoxic for squash plants, although areduction of plant size, possibly caused by host ribosome depurination, was observed.