Low Temperature Conditioning Reduced the Chilling Injury by Regulating Expression of the Dehydrin Genes in Postharvest Huangguan Pear (Pyrus bretschneideri Rehd. cv. Huangguan)

'Huangguan' pear (Pyrus bretschneideri Rehd. cv. Huangguan) fruit is sensitive to chilling injury (CI), which exhibits peel browning spots (PBS) during cold storage. Dehydrin (DHN) is considered to be related to cold tolerance in plants, but its function in postharvest pear fruit during storage remains unclear. In this study, six PbDHNs (PbDHN1-6) genes were identified and characterized, and the PbDHN proteins were sorted into YnKn, SKn and YnSKn according to the major conserved motifs related to the number and location of K-segments, S-segments, and Y-segments. In addition, there were five cold-responsive related cis-acting elements in the promoter region of the PbDHNs. The analysis of fruit quality suggested that compared with a storage temperature at 20 degrees C, a storage temperature of 0 degrees C results in CI in 'Huangguan' pear fruit, while a storage temperature of 10 degrees C and low temperature conditioning (LTC) alleviates the CI. Moreover, gene expression results indicated that the six PbDHNs were markedly enhanced at low temperatures, especially at 0 degrees C. The transcripts of PbDHN1, PbDHN4, PbDHN5 and PbDHN6 were also increased in the fruit stored at 10 degrees C, but they were lower than that at 0 degrees C except PbDHN5. Compared with low temperature storage at 0 degrees C, LTC treatment significantly depressed the expression of PbDHN1, PbDHN2, PbDHN3, PbDHN4, and PbDHN6, while enhanced the mRNA amount of PbDHN5. In conclusion, PbDHN1, PbDHN4, PbDHN5, and PbDHN6 were closely related to the CI, and LTC lowered the CI by down-regulating the expression of PbDHN1, PbDHN4, and PbDHN6 and by up-regulating PbDHN5 in 'Huangguan' pear fruit.