Expression and characterization of putative endo-PG genes in peach genotypes with different patterns of fruit softening

In ripe peach fruits firmness of the flesh is an important quality parameter affecting the shelf-life and market destination of the product. The Melting Flesh (M) locus controls firmness of ripe fruits and has been proposed to encode the enzyme endo-polygalacturonase (endo-PG). Data reported in the literature about Non Melting flesh (NMF) fruits indicate that the lack of endo-PG protein expression is correlated to a partial or total deletion of the gene. Our results on a few genotypes grown in Italy indicate that, as compared to Melting flesh (MF) fruits, NMF fruits show a lower expression/activity of an endo-PG protein accompanied by lower contents in endo-PG mRNA suggesting that the differences between the two phenotypes could be controlled at the transcriptional level. Two endo-PG cDNA clones, corresponding to the full ORFs, were isolated from the different (MF/NMF) fruits and sequenced. Comparison of the sequences showed the presence of 5 SNPs. One of them allowed us to establish the allelic configuration at the M locus, which is respectively heterozygous (+/-) for MF and homozygous (-/-) for NMF fruits. Possible differences at the level of gene promoters are under investigation.