Submitted to: Journal of Plant Growth Regulation
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/26/2007
Publication Date: 6/1/2007
Citation: Barry, C., Giovannoni, J.J. 2007. Ethylene and Fruit Ripening. Journal of Plant Growth Regulation. 26:143-159. Interpretive Summary: Much of our knowledge concerning the mode of action of ethylene in plants has been generated from the use of the triple response screen in Arabidopsis to identify mutants that are either insensitive to ethylene or show enhanced ethylene responses in the absence of exogenous ethylene. The power of Arabidopsis molecular genetics has facilitated the rapid identification of many components of the signalling pathway from an initial mutant phenotype. Here we summarize ethylene signalling research in fruit crop species reviewing primarily research on tomato and how findings differ from the Arabidopsis model. In short, much of the basic ethylene response mechanisms defined in Arabidopsis operates in tomato and additional fruit species but the number and tissue/stage specificity of genes encoding specific ethylene signalling activities differ in comparison to Arabidopsis. In general, at least some crop plants appear to possess more specialized genetic systems encoding ethylene signal transduction components.
Technical Abstract: Experiments designed to down-regulate specific tomato ethylene receptor isoforms using antisense suppression have been reported for LeETR1, NR and LeETR4. Down-regulation of LeETR1 expression in transgenic plants did not alter fruit ripening but resulted in plants with shorter internodes and reduced rates of floral abscission. Down-regulation of NR expression in a wild-type background did not result in any dramatic phenotypes but did result in subtle changes indicative of slightly delayed fruit ripening. Elevated expression of LeETR4 was detected in the NR antisense lines suggesting that this receptor may compensate for loss of NR. Reduction of LeETR4 expression using an antisense transgene resulted in plants with enhanced ethylene sensitivity manifested through extreme epinasty, increased floral abscission, enhanced triple response and accelerated fruit ripening, confirming that LeETR4 acts as a negative regulator of ethylene responses in tomato. Interestingly these phenotypes could be complemented by over-expression of a NR transgene indicating that these two receptors are functionally redundant. Although studies of individual receptor function in tomato requires additional experimentation an obvious difference between the tomato and Arabidopsis systems is evident. Reduction of the receptor LeETR4 in transgenic plants leads to strong phenotypic effects throughout the plant whereas single loss of function mutants in receptors of Arabidopsis do not show dramatic phenotypic changes.