EIN2 and EIN3 in Ethylene Signalling

Ethylene was the first plant hormone for which a receptor-dependent signalling pathway was established. The signal transduction pathway is framed around genetically identified factors encompassing membrane receptors through to intra-cellular regulators and then nuclear transcription factors. Recently, the cellular and biochemical connections among these genetic factors have been characterized to reveal a complex and intertwined signalling scheme. For ethylene signalling, the short-lived ETHYLENE INSENSITIVE2 (EIN2) and ETHYLENE INSENSITIVE3 (EIN3) proteins play central roles, and so regulation of the turnover of these proteins by specific E3 ligases serves as a key regulatory step in the pathway. Two antagonistic mitogen-activated protein kinase (MAPK) cascades that modify EIN3 appear to mediate intra-cellular signalling frommembrane receptors to nuclear transcription factors. The identification of further genomic and genetic components and elucidation of their cellular and biochemical roles in EIN2 and EIN3 regulation are thus required to complete the whole ethylene signal transduction pathway. Such a comprehensive understanding of ethylene signal transduction will provide useful information for the selection of genes that can enhance plant adaptations to unfavourable environmental conditions and so secure food production and plant-based renewable bio-energy for human society.