Strategy of tobacco plant against black shank and tobacco mosaic virus infection via induction of PR-1, PR-4 and PR-5 proteins assisted by medicinal plant extracts

The purpose of this study was to explore the induction strategy of PR proteins in the host plant to overcome black shank and tobacco mosaic virus (TMV) infections, assisted by a mixed plant extract composed of Sophora flavescens, Forsythia suspense and other medicinal plants. To accomplish this, greenhouse experiments were conducted in non-continuously and continuously cropped land. In both types of land, plants treated with the plant extract alone or in combination with fungicides successfully grew even when infected. The superoxide dismutase activity of tobacco plants treated with the plant extract was higher than that of the control plants (P < 0.05). A PR-4 protein was induced (P < 0.01) in response to a black shank infection in the presence of the plant extract by the up-regulation of six chitinase-encoding unigenes involved in carbohydrate metabolism, including amino sugar and nucleotide sugar metabolic pathways. Water course fraction of the mixed plant extract played a key role in PR-4 induction in the presence of black shank. In response to a TMV infection, the plant extract primarily induced PR-1 (P < 0.01) by up-regulating two unigenes involved in the development of plant-pathogen interactions and the membrane transport-plant hormone signal transduction pathway. The petroleum ether and normal butanol fractions contributed to PR-1 induction against TMV infection. The host plants used PR-5 as a synergetic protein by accumulating five osmotin encoding unigenes against black shank in continuously cropped soil and TMV in non-continuously cropped soil. The normal butanol fraction of the mixed plant extract was responsible for PR-5 up-regulation. In general, the synergetic effects of four polar fractions of the mixed plant extract, the interaction of the host plant and the mixed plant extract and the synergetic effects of the PR proteins of the host plant were the basis of an intelligent host plant strategy.