ETHYLENE RECEPTOR EXPRESSION IS REGULATED DURING FRUIT RIPENING, FLOWER SENESCENCE AND ABSCISSION

Using the Arabidopsis ethylene receptor ETR1 as a probe, we have isola ted a tomato homologue (tETR) from a ripening cDNA library. The predic ted amino acid sequence is 70% identical to ETR1 and homologous to a v ariety of bacterial two component response regulators over the histidi ne kinase domain. Sequencing of four separate cDNAs indicates that tET R lacks the carboxyl terminal response domain and is identical to that encoded by the tomato Never ripe gene. Ribonuclease protection showed tETR mRNA was undetectable in unripe fruit or pre-senescent flowers, increased in abundance during the early stages of ripening, flower sen escence, and in abscission zones, and was greatly reduced in fruit of ripening mutants deficient in ethylene synthesis or response. These re sults suggest that changes in ethylene sensitivity are mediated by mod ulation of receptor levels during development.