Biochemical and genetic mechanisms used by plant growth-promoting bacteria

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The term "plant growth-promoting bacteria" describes soil bacteria that are involved in a beneficial association with plants (often with the roots). These bacteria use a variety of mechanisms to facilitate plant growth. However, in order to make the use of plant growth-promoting bacteria in agriculture, horticulture and environmental cleanup, more efficacious, predictable and reproducible, it is necessary to first understand the fundamental genetic and biochemical mechanisms that govern the relationship between these organisms and plants. In this regard, one of the major mechanisms used by plant growth-promoting bacteria involves the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase which cleaves the compound ACC, the immediate precursor of the phytohormone ethylene in all higher plants. Plant growth-promoting bacterial strains that contain ACC deaminase provide a wide range of different plant species with a significant level of protection from the damage caused by various environmental stresses including phytopathogens, flooding, heavy metals, drought, temperature extremes, the presence of organic environmental contaminants, and high salt. In the work that is proposed here: the details of how plant growth-promoting bacteria and plants impact one another's gene expression will be elaborated; some of the details of how symbiotic bacteria with ACC deaminase function will be investigated; and efforts will be made to understand how plant growth-promoting bacteria that bind only to a plant's roots differ from those that colonize the interior of the plant in their promotion of plant growth.