Ethylene is involved in the regulation of many growth and developmental processes in plants. Signaling pathways of the hormone are activated by five receptors, which are localized in membranes of endoplasmic reticulum and are similar to bacterial two-component histidine kinases. In the air, ethylene receptors activate CTR1 protein, which is a negative regulator (repressor) of nuclear protein--EIN2. In turn, EIN2 is an activator of transcriptional factors cascade responsible for the regulation of the expression of ethylene response genes. The level of EIN3, as well as other elements of ethylene signal transduction pathway, is subjected to complicated regulations on transcriptional and posttranslational levels, in which other internal and environmental factors are involved.