Identification of woolliness response genes in peach fruit after post-harvest treatments

Abstract

Woolliness is a physiological disorder of peaches and nectarines that becomes apparent when fruit are ripened after prolonged periods of cold storage. This disorder is of commercial importance since shipping of peaches to distant markets and storage before selling require low temperature. However, knowledge about the molecular basis of peach woolliness is still incomplete. To address this issue, a nylon macroarray containing 847 non-redundant expressed sequence tags (ESTs) from a ripe peach fruit cDNA library was developed and used. Gene expression changes of peach fruit (Prunus persica cv. O'Henry) ripened for 7 d at 21 degrees C (juicy fruit) were compared with those of fruit stored for 15 d at 4 degrees C and then ripened for 7 d at 21 degrees C (woolly fruit). A total of 106 genes were found to be differentially expressed between juicy and woolly fruit. Data analysis indicated that the activity of most of these genes (>90%) was repressed in the woolly fruit. In cold-stored peaches (cv. O'Henry), the expression level of selected genes (cobra, endopolygalacturonase, cinnamoyl-CoA-reductase, and rab11) was lower than in the juicy fruit, and it remained low in woolly peaches after ripening, a pattern that was conserved in woolly fruit from two other commercial cultivars (cv. Flamekist and cv. Elegant Lady). In addition, the results of this study indicate that molecular changes during fruit woolliness involve changes in the expression of genes associated with cell wall metabolism and endomembrane trafficking. Overall, the results reported here provide an initial characterization of the transcriptome activity of peach fruit under different post-harvest treatments.

Fig. 1.

Gene expression analyses after post-harvest treatments and in fruit from different cultivars. Four genes (cob, endoPG, CCR, and rab11) whose expression levels were decreased in woolly fruit, according to the macroarray data, were assayed by qPCR using cDNAs from different post-harvest treatments and cultivars. For peaches cv. O'Henry (O), the following samples were analysed: (c1) ripened and juicy fruit; (c2) cold-stored, non-ripened fruit; and (c3) cold-stored, ripened, and woolly. For peaches cv. Elegant Lady (E) and cv. Flamekist (F), samples from: (c1) ripened and juicy fruit and (c3) cold-stored, ripened, and woolly fruit were assayed. For each gene, the relative abundance of mRNA was normalized towards tubulin in the corresponding samples. The results are presented as a percentage of the highest value of relative abundance. Different letters between each treatment represent significant differences at P < 0.05 by LSD test.