Expression analysis of five tobacco EIN3 family members in relation to tissue-specific ethylene responses

Ethylene induces different sets of genes in different tissues and at different stages of development. To investigate whether these differential responses are caused by differential expression of members of the EIN3 family transcription factors, five tobacco family members were isolated. They can be divided into three subgroups, which is probably due to the amphidiploid nature of tobacco. In phylogenetic analysis, each of the subgroups clustered with one of the three tomato EIL proteins and all NtEILs proved to be most homologous to Arabidopsis EIN3 and EIL1. Although organ-specific ethylene responses have been observed before, northern blot analysis showed that all NtEILs were expressed in all organs. To study differential NtEIL expression at the cellular level, in situ hybridization was used on the tobacco ovary. It was found that different ovary tissues displayed variable ethylene-induced expression of two ethylene-responsive marker genes. By contrast, no differences were found in expression level or tissue-specificity for any of the NtEILs in the ovary, before or after ethylene treatment. This indicates that the organ and tissue-specific ethylene responses are not caused by differential expression of NtEIL family members. These results support a model in which the developmental signals that regulate the tissue-specific responses are integrated with the ethylene signal downstream of a common primary ethylene-signalling pathway.