Auxin, a plant hormone, is also produced by certain bacteria, playing a significant role in microbial-plant interactions. Bacteria such as Agrobacterium and Pseudomonas can synthesize auxin (indole-3-acetic acid, IAA), which can interfere with plant development by disrupting auxin balance. IAA is also a signaling molecule in some microorganisms, facilitating reciprocal communication between microbes and plants. In Arabidopsis, auxin signaling is part of the plant's defense against phytopathogenic bacteria, with exogenous auxin enhancing susceptibility to pathogens. Bacteria produce IAA through various pathways, including the indole-3-acetamide (IAM) pathway and the indole-3-pyruvate (IPA) pathway. The IAM pathway involves tryptophan monooxygenase and IAM hydrolase, while the IPA pathway includes aminotransferase, decarboxylase, and dehydrogenase. Other pathways, such as the tryptamine and tryptophan side-chain oxidase pathways, also contribute to IAA synthesis. Some bacteria can produce IAA independently of tryptophan, though this is less well understood. IAA biosynthesis is regulated by environmental factors and genetic elements. For example, in Azospirillum brasilense, the ipdC gene is strictly regulated, with IAA production increasing during stationary phase. IAA also acts as a signal molecule in bacteria, influencing gene expression and virulence. In plant-pathogenic bacteria like Agrobacterium tumefaciens, IAA inhibits vir gene expression, indicating its role in plant transformation. In symbiotic bacteria such as Rhizobium, IAA production is involved in nodule formation and nitrogen fixation. Bacteria can also promote plant growth through IAA biosynthesis, along with other mechanisms like nitrogen fixation and ACC deaminase activity. Auxin signaling in plants is also linked to defense responses against pathogens, with exogenous auxin increasing susceptibility. Overall, auxin plays a crucial role in microbial-plant interactions, influencing both pathogenic and beneficial relationships. Understanding the regulation and function of IAA in bacteria is essential for advancing research in plant-microbe interactions and improving crop growth and yield.Auxin, a plant hormone, is also produced by certain bacteria, playing a significant role in microbial-plant interactions. Bacteria such as Agrobacterium and Pseudomonas can synthesize auxin (indole-3-acetic acid, IAA), which can interfere with plant development by disrupting auxin balance. IAA is also a signaling molecule in some microorganisms, facilitating reciprocal communication between microbes and plants. In Arabidopsis, auxin signaling is part of the plant's defense against phytopathogenic bacteria, with exogenous auxin enhancing susceptibility to pathogens. Bacteria produce IAA through various pathways, including the indole-3-acetamide (IAM) pathway and the indole-3-pyruvate (IPA) pathway. The IAM pathway involves tryptophan monooxygenase and IAM hydrolase, while the IPA pathway includes aminotransferase, decarboxylase, and dehydrogenase. Other pathways, such as the tryptamine and tryptophan side-chain oxidase pathways, also contribute to IAA synthesis. Some bacteria can produce IAA independently of tryptophan, though this is less well understood. IAA biosynthesis is regulated by environmental factors and genetic elements. For example, in Azospirillum brasilense, the ipdC gene is strictly regulated, with IAA production increasing during stationary phase. IAA also acts as a signal molecule in bacteria, influencing gene expression and virulence. In plant-pathogenic bacteria like Agrobacterium tumefaciens, IAA inhibits vir gene expression, indicating its role in plant transformation. In symbiotic bacteria such as Rhizobium, IAA production is involved in nodule formation and nitrogen fixation. Bacteria can also promote plant growth through IAA biosynthesis, along with other mechanisms like nitrogen fixation and ACC deaminase activity. Auxin signaling in plants is also linked to defense responses against pathogens, with exogenous auxin increasing susceptibility. Overall, auxin plays a crucial role in microbial-plant interactions, influencing both pathogenic and beneficial relationships. Understanding the regulation and function of IAA in bacteria is essential for advancing research in plant-microbe interactions and improving crop growth and yield.