Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 16, 2002
Publication Date: June 11, 2002
Citation: Bassett, C.L., Artlip, T.S., Callahan, A.M. Characterization of the peach homologue of the ethylene receptor ppetr1, reveals some unusual features regarding transcript processing. Planta 215:679-688, 2002. Interpretive Summary: A major problem for the grocer and consumer is to maintain fruit quality against the continuous natural progression of fruit from ripe to overripe to decayed. Damage to the fruit before it reaches the store also affects quality, since wounds and bruises are not only unsightly, but also provide an ideal environment for decay-causing microbes. Interestingly, both problems are associated with the gaseous plant hormone, ethylene. This hormone not only causes accelerated 'aging' of fruit, but is also produced at wound sites. Response to ethylene at wound sites may lead to increased discoloration and 'mushiness' which detract from the overall quality of the fruit. A plant cannot respond to ethylene unless it produces receptor proteins. We have isolated the gene encoding one of these receptor proteins, called ETR1, from peach and followed its expression in developing fruit and in wounded tissues. One of the unique discoveries made was that three different, but related versions of the receptor protein could be synthesized from this single gene. We also showed that expression of ETR1 in wounded peach fruit was very different from expression in wounded leaves. Our results suggest that modification of this gene could be used to decrease the rate of peach fruit ripening and reduce some of the damage occurring at wound sites. Such manipulation could lead to better quality fruit available for the consumer and a reduction in the amount of dollars lost after harvesting due to aging and/or wounding of fruit.
Technical Abstract: To identify which processes in peach, Prunus persica, are associated with changes in ethylene perception, we cloned and characterized a peach homologue of the gene encoding the ethylene receptor, ETR1. A fragment of the peach gene, PpETR1, obtained via PCR using degenerate primers against peach genomic DNA was used to screen a cDNA library made from ripening fruit. The resulting cDNA and subsequent 3' RACE clones indicate that the PpETR1 coding region is highly similar to other ETR1 homologues. However, the mRNA undergoes unusual alternative splicing that results in three different mature transcripts. Use of an alternative 3' splice site to remove the last intron in PpETR1a results in a polypeptide that is missing three amino acids from the receiver-like domain. Retention of the terminal intron occurs in PpETR1b which, if translated, would result in a truncated protein lacking a receiver-like domain. Fruit from three cultivars with substantially different ripening times were examined from 7 to 130 days after bloom using RT-PCR to characterize expression of the intron-retaining and fully spliced mRNAs. There were only slight differences in the abundance of these mRNAs among cultivars during fruit development; however, one of the slow ripening cultivars showed a significant increase in expression of the unspliced mRNA in pre-climacteric fruit. Variations in PpETR1 transcript abundance in wounding experiments with leaves and fruit indicate that the properly spliced and unspliced versions show opposite accumulation patterns in the two tissues. In contrast to previous reports, the fully spliced form in peach appears to accumulate in wounded fruit.