Characterization of two putative ethylene receptor genes expressed during peach fruit development and abscission

Two peach genes homologous to the Arabidopsis ethylene receptor genes ETR1 and ERS1, named Pp‐ETR1 and Pp‐ERS1 respectively, have been isolated and characterized. Pp‐ETR1 and Pp‐ERS1 are conserved in terms of exon numbers and intron positions, although the first and fifth introns of Pp‐ETR1 have an unusual length. In addition, two putative polyadenylation sites, that may cause an incomplete splicing at the 3′ terminus, are present in the fifth intron. A motif of 28 nt, which shows high homology with ethylene responsive elements found in promoters of genes up‐regulated by ethylene, is present in the promoter region of Pp‐ERS1. Expression analysis, carried out by quantitative RT‐PCR, was performed during fruit development and ripening, and leaf and fruitlet abscission. The level of Pp‐ETR1 transcripts remained unchanged in all the tissues and developmental stages examined, whereas Pp‐ERS1 mRNA abundance increased in ripening mesocarp, in leaf and fruitlet activated abscission zones, and following propylene application. 1‐methylcyclopropene (1‐MCP), an inhibitor of ethylene action, did not affect Pp‐ETR1 transcription, while it down‐regulated Pp‐ERS1. A rise in ethylene evolution, accompanied by an increase of Pp‐ERS1 transcript accumulation occurred within 24 h from the end of 1‐MCP treatment. These results indicate that Pp‐ERS1 might play a role in abscission and ripening.