Ethylene-regulated gene expression in tomato fruit: characterization of novel ethylene-responsive and ripening-related genes isolated by differentialdisplay

Differential display was used to isolate early ethylene-regulated-genes fro m late immature green tomato fruit in order to obtain a broader understandi ng of the molecular basis by which ethylene coordinates the ripening proces s. Nineteen novel ethylene-responsive (ER) cDNA clones were isolated that f ell into three classes: (i) ethylene up-regulated (ii) ethylene downregulat ed, and (iii) transiently induced. Expression analysis revealed that ethyle ne-dependent changes in mRNA accumulation occurred rapidly (15 min) for mos t of the ER clones. The predicted proteins encoded by the ER genes are puta tively involved in processes as diverse as primary metabolism, hormone sign alling and stress responses. Although a number of the isolated ER clones co rrespond to genes already documented in other species, their responsiveness to ethylene is described here for the first time. Among the ER clones shar ing high homology with regulatory genes, ER43, a putative GTP-binding prote in, and ER50, a CTR1-like clone, are potentially involved in signal transdu ction. ER24 is homologous to the multiprotein bridging factor MBF1 involved in transcriptional activation, and finally, two clones are homologous to g enes involved in post-transcriptional regulation: ER49, a putative translat ional elongation factor, and ER68, a mRNA helicase-like gene. Six ER clones correspond to as yet unidentified genes. The expression studies indicated that all the ER genes are ripening-regulated, and, depending on the clone, show changes in transcript accumulation either at the breaker, turning, or red stage. Analysis of transcript accumulation in different organs indicate d a strong bias towards expression in the fruit for many of the clones. The potential roles for some of the ER clones in propagating the ethylene resp onse and regulating fruit ripening are discussed.