Submitted to: Plant Signaling and Behavior
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/16/2013
Publication Date: 5/2/2013
Publication URL: http://handle.nal.usda.gov/10113/56699
Citation: Cooper, B. 2013. Separation anxiety: An analysis of ethylene-induced cleavage of EIN2. Plant Signaling and Behavior. 8(7):e24721-1-e24721-5. Interpretive Summary: Ethylene is an important gas that induces fruit ripening and plant development. Ethylene influences plant proteins that act as switches that turn off and on the molecular processes that lead to ripening and development. Qiao et al. recently reported in the journal Science the discovery of the biochemistry that regulates the molecular switches for ethylene signaling. It appears, however, based on the evidence in the Qiao et al. report and evidence performed independently at other research labs that Qiao et al. misinterpreted some data and that some, but not all, of their conclusions may be incorrect. The purpose of this research report is to notify other scientists of this potential discrepancy and to encourage Qiao et al. to substantiate their claims. Debating the meaning of results is a common, natural part of scientific discovery and discourse and leads to new experiments and findings that bolster or overturn claims. Therefore, this report is most likely to influence scientists at universities, government agencies and companies who are studying fruit ripening and plant development and who are trying to use up-to-date knowledge to better control these processes in order to produce higher quality fruits and vegetables.
Technical Abstract: Since the discovery of the CTR1 protein kinase and the endoplasmic reticulum (ER)-localized EIN2 protein nearly 20 y ago, plant biologists have wondered how these proteins respectively serve as negative and positive regulators of ethylene-mediated signal transduction in plants. Now with the publication of four studies, it can be concluded that in the absence of ethylene (ET) in Arabidopsis thaliana, CTR1 phosphorylates EIN2 thereby inactivating ET signal transduction, while in the presence of ET, CTR1 no longer phosphorylates EIN2 and the cytosolic C-terminus of EIN2 is released from the ER to translocate to the nucleus to promote gene transcription. Chen et al. (2011) showed that EIN2 is differentially phosphorylated at amino acids (a.a.) S645 and S924 after ET treatment. Ju et al. (2012) then proved that CTR1 phosphorylates EIN2 at those positions and that the lack of phosphorylation at S645 and S924 leads to the translocation of an EIN2 C-terminus peptide. Wen et al. (2012) and Qiao et al. (2012) also demonstrated ET-induced translocation of an EIN2 C-terminus peptide, while Qiao et al. (2012) proved that EIN2 has a nuclear localization signal sequence required for translocation, confirmed phosphorylation at S645 and said that proteolytic cleavage occurs at S645 in absence of phosphorylation there. Despite the revelation of this elegant switch, there are contradictory indications for specific cleavage at EIN2 S645. This article investigates the data and concludes that EIN2 may be cleaved at alternative positions.