Characterization of Rhodopseudomonas palustris population dynamics on tobacco phyllosphere and induction of plant resistance to Tobacco mosaic virus infection

Although many biocontrol bacteria can be used to improve plant tolerance to stresses and to promote plant growth, the hostile environmental conditions on plant phyllosphere and the limited knowledge on bacterial colonization on plant phyllosphere minimized the beneficial effects produced by the biocontrol bacteria. Rhodopseudomonas palustris strain GJ-22 is known as a phyllosphere biocontrol agent. In this paper we described detailed processes of strain GJ-22 colony establishment at various colonization stages. We have shown that the preferable location sites of bacterial aggregates on leaf phyllosphere are grooves between plant epidermal cells. In this study, we categorized bacterial colonies into four phases. Analyses of expressions of plant defense-related genes showed that, starting from Phase III, bacterial cells in the Type 3 and Type 4 colonies started produce unidentified signals to induce host defense again Tobacco mosaic virus infection. To our knowledge, this is the first report focused on the colonization process of a phyllosphere biocontrol agent.