An Ethylene-Binding Protein, AzoETR1, in <i>Azospirillum brasilense</i> Sp7

Ethylene is an important phytohormone produced by higher plants where it plays numerous roles in growth and development and in mediating responses to many environmental factors. The genome sequence of the soil alphaproteobacterium A. brasilense suggests that it encodes a homolog of an ethylene-binding protein (AzoETR1), similar to that found in plants. AzoETR1 also possesses a conserved histidine kinase domain with the azoETR1 gene encoded upstream of a putative response regulator. Therefore, this ethylene binding protein may be part of a two-component signal transduction pathway. Recombinant expression of the ethylene-binding domain of AzoETR1 in Pichia pastoris followed by an in vitro ethylene binding experiment confirmed ethylene binding, which suggests that this domain in A. brasilense could bind gaseous ethylene. Our current goal is to identify the role of ethylene sensing in the life cycle of A. brasilense. Given that A. brasilense colonizes the rhizosphere, we are testing the hypothesis that binding of ethylene to AzoETR1 modulates plant-microbe interactions in the rhizosphere. We focused on motility and growth because ethylene perception is implicated in modulating motility and chemotaxis in another bacterial species. In the cyanobacteria, Synechocystis, ethylene is implicated in phototaxis. Our objective is to expand on the known functions for ethylene by uncovering new information on the effects ethylene has on soil-dwelling bacteria.