Investigating the Regulation of Indole-3-Acetic Acid Production By the Plant Associated Microbe <i>Pantoea</i> sp. YR343

The auxin indole-3-acetic acid (IAA) plays a central role in plant growth and development and many plant-associated microbes produce IAA. Several IAA biosynthetic pathways have been identified in microbes which use the precursor tryptophan. Pantoea sp. YR343, which was isolated from the Populus deltoides rhizosphere, is a robust plant root colonizer that produces IAA. Using genomic and metabolomics analyses, we predicted that the indole-3-pyruvate (IPA) pathway is the major pathway in Pantoea sp. YR343 for IAA production. To better understand IAA biosynthesis and the effects of IAA exposure on cell physiology, we performed proteomics on Pantoea sp. YR343 grown in the presence of tryptophan or IAA. These data indicate that indole-3-pyruvate decarboxylase, a major enzyme in the IPA pathway, is upregulated in the presence of both tryptophan and IAA. Moreover, exposure to IAA induced changes in the proteome, including upregulation of proteins predicted to function in carbohydrate and amino acid transport and EPS biosynthesis. Finally, we constructed a mutant in which the ipdC gene was disrupted. The ΔipdC mutant showed a significant decrease in IAA production, but was still able to efficiently colonize poplar, suggesting that microbial IAA production is not required for initiation of plant association.