Isolation and characterization of four ethylene perception elements and their expression during ripening in pears (Pyrus communis L.) with/without cold requirement

Pear (Pyrus communis L.) are climacteric fruit: their ripening is associated with a burst of autocatalytic ethylene production. Some late pear cultivars, such as Passe-Crassane (PC) require a long (80 d) chilling treatment before the fruit will produce autocatalytic ethylene and ripen. As the cold requirement is linked to the capacity to respond to ethylene (or its analogue, propylene), three pear cDNAs homologous to the Arabidopsis ethylene receptor genes At-ETR1, At-ERS1, and At-ETR2, designated Pc-ETR1a (AF386509), Pc-ERS1a (AF386515), and Pc-ETR5 (AF386511), respectively, have been isolated. A pear homologue of the Arabidopsis ethylene signal transduction pathway gene At-CTR1, called Pc-CTR1 (AF386508) has also been isolated. The search of the genomic sequences for Pc-ETR1a and Pc-ERS1a resulted in the isolation of four related genomic clones Pc-DETR1a (AF386525), Pc-DETR1b (AF386520), Pc-DERS1a (AF386517), and Pc-DERS1b (AF386522). Analysis of transcript levels for the four cDNAs in PC and pear fruit genotypes with little or no cold requirement revealed that Pc-ETR1a expression increased during chilling treatment, and Pc-ETR1a, Pc-ERS1a, Pc-ETR5, and Pc-CTR1 expression increased during fruit ripening and after ethylene treatment. Whether the differences in the ethylene response elements studied here are the cause or an effect of the cold requirement in PC fruit is discussed.