Ethylene–a key arbitrator to plant–fungal symbiotic interactions?

Plant roots often form symbiotic interactions with soilborne fungi. The symbiotic structures formed during this interaction require a host of signalling molecules to set up a balanced and mutually beneficial interaction between both organisms. One hormone implicated in contributing to this process on behalf of the plant is ethylene. As a gas, ethylene serves as an effective signalling agent both within an organism and as a longer-distance signal between organisms, as it can diffuse through both air and soil. Ethylene is produced by plants as well as soilborne fungi that form a symbiotic relationship with plant roots. Ethylene has been shown to have an effect on root development in plants (Kaska et al., 1999) and to be released during the establishment of root–fungal symbiosis (Rupp et al., 1989). Although the exact role of ethylene during this process has not been fully elucidated, it can at times aid or inhibit the colonization by fungi. While ethylene has a role as a signalling agent in a number of different plant processes, it is commonly known as the ‘stress’ hormone released by the plant in order to recruit defences against both biotic and abiotic stressors