Changes in the Expression of Genes Involved in Ethylene Signalling in Peach Fruits with Different Flesh Texture and Softening Patterns

Melting flesh (MF) and non-melting flesh (NMF) peaches show different texture and firmness and different ethylene levels. The MF phenotype is linked to the presence of high levels of an active ripening-related endopolygalacturonase (endoPG). In ’Oro A‘ the predicted amino acidic sequence of endoPG protein is very similar to that of MF ’Bolero‘ but the levels of the active endoPG protein and Pp-endoPG transcripts are very low, suggesting that expression of the Pp-endoPG gene could be transcriptionally regulated. Regulation of Pp-endoPG gene expression could be related to possible differences in ethylene perception/transduction in fruit flesh tissues. Fruit of two NMF (‘Oro A’ and ‘Andross’) and two MF (‘Bolero’ and ‘Springcrest’) peach cultivars were analyzed for levels of ethylene and of transcripts of a few genes involved in ethylene signalling. Ethylene levels were lower in MF than in NMF fruit; the levels of Pp-ERS1, Pp-ETR2 and Pp-CTR1 transcripts were lower in MF fruit, consistent with their suggested role of negative regulators of the ethylene response. The levels of transcripts of Pp-ERF1, which is involved in response induction, were higher in MF and well related to higher levels of Pp-endoPG transcripts. The Pp-endoPG gene is present as one allele (m) in ‘Oro A’ and as two alleles (m and M) in ‘Bolero’; sequence analysis of a 1970 bp sequence upstream of ATG of the Pp-endoPG-m allele showed presence of potential regulatory sequences associated with hormone responses. Preliminary results obtained by partial isolation and sequencing of the 124 bp sequence upstream of ATG of the Pp-endoPG-M allele of ‘Bolero’ showed deep differences compared to the Pp-endoPG-m allele. Work is now in progress to complete sequencing of this region of the ‘Bolero’ Pp-endoPG-M allele.