Body of Abstract: Fusaricidins A and B (FA and FB), isolated from endophytic bacteria Paenibacillus ottowii, belong to the class of lipodepsipeptides. Fusaricidins are active against a variety of fungi and bacteria. To assess the impact of FA and FB on plant growth and health, we conducted experiments on several plant species. The mixture of fusaricidins A and B (1:1 of FA and FB) did not exhibit a notable inhibition of germination of bentgrass (Agrostis stolonifera) or lettuce (Lactuca sativa) at various concentrations. However, it showed strong post-germination activity with IC50 of 0.9 µM. At the concentration of 8.2 µM, it strongly inhibited the growth of monocot Lemna paucicostata, a common duckweed, and Arabidopsis seedlings. The pure form of fusaricidin A displayed significant phytotoxicity against Arabidopsis with an IC50 of 2.8 µM. As part of the mode of action studies, we tested the chlorophyll fluorescence emitted from Arabidopsis leaves. The results indicated that photosynthesis may not be the primary target of the compound. However, electric conductivity tests indicated that it caused a plasma-membrane disintegration, most likely a result of the presence of a lipophilic β-hydroxy fatty acid chain in the compound structure. The RNA-seq data generated from the treatments with fusaricidin A revealed a strong induction of genes related to plant response to bacteria. The progress to-date on the transcriptome analysis will be presented.