EIN3

EIN3, short for ETHYLENE INSENSITIVE3, is a plant transcription factor that serves as a central regulator of the ethylene signaling pathway. It belongs to the EIN3-like (EIL) family of transcription factors found in many angiosperms, including Arabidopsis thaliana. EIN3 proteins accumulate in the nucleus in response to ethylene and activate transcription of ethylene-responsive genes.

In the canonical ethylene signaling model, ethylene binding to its receptors suppresses CTR1 kinase activity, allowing a signal that stabilizes the C-terminal domain of EIN2. The EIN2 C-terminus then promotes stabilization and accumulation of EIN3 and its close relatives EIL1 by inhibiting the F-box proteins EBF1 and EBF2, which normally target EIN3 for proteasomal degradation. Once stabilized, EIN3 binds to target promoters, including the ERF1 gene and other Ethylene Response Factor (ERF) genes, to initiate transcription programs that drive physiological responses such as the classical triple response in light-grown seedlings, as well as leaf senescence, fruit ripening, and defense reactions.

EIN3 proteins contain a conserved EIN3 DNA-binding domain that enables recognition of ethylene-responsive elements in target promoters. The activity of EIN3 is modulated at multiple levels, including proteasomal turnover, interactions with EIL proteins, and cross talk with other signaling pathways.

Loss-of-function mutations in EIN3 typically result in reduced ethylene sensitivity, while ectopic stabilization can enhance ethylene responses. Because of their conserved role and redundancy within the EIL family, multiple EIN3-like factors can partially compensate for each other to regulate ethylene responses across plant species.