A bulk segregant gene expression analysis of a peach population reveals components of the underlying mechanism of the fruit cold response

Abstract

Peach fruits subjected for long periods of cold storage are primed to develop chilling injury once fruits are shelf ripened at room temperature. Very little is known about the molecular changes occurring in fruits during cold exposure. To get some insight into this process a transcript profiling analyses was performed on fruits from a PopDG population segregating for chilling injury CI responses. A bulked segregant gene expression analysis based on groups of fruits showing extreme CI responses indicated that the transcriptome of peach fruits was modified already during cold storage consistently with eventual CI development. Most peach cold-responsive genes have orthologs in Arabidopsis that participate in cold acclimation and other stresses responses, while some of them showed expression patterns that differs in fruits according to their susceptibility to develop mealiness. Members of ICE1, CBF1/3 and HOS9 regulons seem to have a prominent role in differential cold responses between low and high sensitive fruits. In high sensitive fruits, an alternative cold response program is detected. This program is probably associated with dehydration/osmotic stress and regulated by ABA, auxins and ethylene. In addition, the observation that tolerant siblings showed a series of genes encoding for stress protective activities with higher expression both at harvest and during cold treatment, suggests that preprogrammed mechanisms could shape fruit ability to tolerate postharvest cold-induced stress. A number of genes differentially expressed were validated and extended to individual genotypes by medium-throughput RT-qPCR. Analyses presented here provide a global view of the responses of peach fruits to cold storage and highlights new peach genes that probably play important roles in the tolerance/sensitivity to cold storage. Our results provide a roadmap for further experiments and would help to develop new postharvest protocols and gene directed breeding strategies to better cope with chilling injury.