Characterization of the peach homologue of the ethylene receptor, PpETR1, reveals some unusual features regarding transcript processing

Abstract.

To identify which processes in peach, Prunus persica [L.] Batsch., 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 potentially 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 within 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 substantial increase in expression of the unspliced mRNA in pre-climacteric fruit. Variations in PpETR1 transcript abundance in wounding experiments indicate that the properly spliced and unspliced versions have different accumulation patterns in fruit, whereas both are essentially constitutive in leaves. These observations indicate that changes in ethylene sensitivity may occur during wounding in fruit.