Functional analysis of peach ACC-oxidase promoters in transgenic tomato and in ripening peach fruit.

To investigate the transcriptional regulation of two 1-aminocyclopropane-1-carboxylate (ACC) oxidase (ACO) genes of peach, chimeric fusions between β-glucuronidase (GUS) reporter gene, and Pp-ACO1 and Pp-ACO2 promoters have been constructed and introduced in tomato (cv Microtom). Pp-ACO1 promoter is able to induce in transgenic tomato plants the same pattern of expression observed in peach. In fact, Pp-ACO1-GUS activity was localized in leaf blade, ovary, leaf and fruit abscission zones and pericarp, and it is up-regulated by propylene and wounding. A gradient of transcript accumulation has been observed in ripening fruit tissues: in tomato it decreased moving from the inner to the outer pericarp, while in peach the opposite occurred. This different behavior could be related to the fruit type (berry vs. drupe). In order to identify cis-acting element involved in ethylene induction of Pp-ACO1, portions of its promoter fused with the GUS gene have been constructed and used in peach fruit transient activity assay. The deletion analysis has shown that a region located between -716 and -346 bp, containing an ethylene-responsive element (ERE), is responsible for the higher stimulation by the gas. In addition, two auxin-responsive elements (AUXre), probably responsible for the auxin suppression of the propylene induction of Pp-ACO1 gene expression, are present upstream from EREs. Pp-ACO2 promoter is able to drive the expression in vascular bundles of immature and ripe fruit, senescent leaf blade, and in fruit and leaf abscission zones. In peach, Pp-ACO2 mRNA is detected only in immature fruit, epicotyl and root of seedling. This discrepancy might be imputed to a lesser stability and translation of Pp-ACO2 mRNA in comparison to that of chimeric one