The plant hormone ethylene regulates many aspects of growth and development. Loss-of-function mutations in ETHYLENE INSENSITIVE2 (EIN2) result in ethylene insensitivity in Arabidopsis, indicating an essential role of EIN2 in ethylene signaling. However, little is known about the role of EIN2 in species other than Arabidopsis. To gain a better understanding of EIN2, a petunia (Petunia 3 hybrida cv Mitchell Diploid [MD]) homolog of the Arabidopsis EIN2 gene (PhEIN2) was isolated, and the role of PhEIN2 was analyzed in a wide range of plant responses to ethylene, many that do not occur in Arabidopsis. PhEIN2 mRNA was present at varying levels in tissues examined, and the PhEIN2 expression decreased after ethylene treatment in petals. These results indicate that expression of PhEIN2 mRNA is spatially and temporally regulated in petunia during plant development. Transgenic petunia plants with reduced PhEIN2 expression were compared to wild-type MD and ethylene-insensitive petunia plants expressing the Arabidopsis etr1-1 gene for several physiological processes. Both PhEIN2 and etr1-1 transgenic plants exhibited significant delays in flower senescence and fruit ripening, inhibited adventitious root and seedling root hair formation, premature death, and increased hypocotyl length in seedling ethylene response assays compared to MD. Moderate or strong levels of reduction in ethylene sensitivity were achieved with expression of both etr1-1 and PhEIN2 transgenes, as measured by downstream expression of PhEIL1. These results demonstrate that PhEIN2 mediates ethylene signals in a wide range of physiological processes and also indicate the central role of EIN2 in ethylene signal transduction.The plant hormone ethylene is involved in a wide range of developmental processes in many plant species (Abeles et al., 1992). In Arabidopsis, ethylene signaling is mediated by a complex multicomponent pathway (Kieber, 1997;Guo and Ecker, 2004). ETR1, which encodes a His kinase with homology to bacterial two-component regulators, has been identified as an ethylene receptor (Chang et al., 1993). A total of five ethylene receptor genes have been cloned from Arabidopsis; ETR1, ETR2, ERS1, ERS2, and EIN4 (Hua et al., 1995Sakai et al., 1998). Analysis of loss-offunction mutations in multiple receptors has shown that the receptors are negative regulators of ethylene responses (Hua and Meyerowitz, 1998). The receptors are believed to act through CTR1, which is homologous to the Raf family of Ser/Thr kinases and negatively regulates ethylene signaling (Kieber et al., 1993;Huang et al., 2003). Multiple EIN3/EIL (EIN3-like) transcription factors have also been identified in Arabidopsis (Chao et al., 1997). The EIN3 family contains several proteins that bind an ethylene response element in the promoter of a downstream transcription factor, ERF1 (Solano et al., 1998).An additional component of the ethylene-signaling pathway, EIN2, was isolated from Arabidopsis (Alonso et al., 1999). EIN2 is a single-copy gene and is the only gene known in which loss...

No abstract