Effects of Freezing Stress on the Expression of Fatty Acid Desaturase (FAD2, FAD6 and FAD7) and Beta-Glucosidase (BGLC) Genes in Tolerant and Sensitive Olive Cultivars

In this study, the effect of freezing stress on expression of fatty acid desaturases (FAD2-2, FAD6 and FAD7) and beta-glucosidase (BGLC) genes was investigated in freezing- tolerant (“Fishomi”) and sensitive (“Zard”) olive (Olea europaea L.) cultivars. The olive cultivars were exposed to freezing stress (–10°C) at three different times points (1, 4 and 8 h), followed by a recovery stage. The degree of cell membrane damage was determined by measurement of leaves ion leakage of two olive cultivars both at freezing and recovery condition. The results indicated that ion leakage of cv. “Fishomi” was significantly lower than cv. “Zard” when exposed to the freezing stress and recovery condition. Furthermore, BGLC gene expression level in cv. “Zard” significantly suppressed 8 h after freezing stress. At the recovery period, its expression increased about three-fold at cv. “Fishomi”. However, it was suppressed in cv. “Zard” at recovery period. FAD genes expression pattern in cv. “Fishomi” was different from that in cv. “Zard”. FAD2 expression level in cv. “Fishomi” initially increased at the first 1 h and 4 h of freezing stress time and thereafter, decreased to control level over 8 h. Following recovery period, FAD2 gene expression level in cv. “Fishomi” increased up 5-fold. While, no expression detected in “Zard” at any time point or recovery period. The expression of FAD6 and FAD7 genes showed similar patterns at both cultivars. FAD6 and FAD7 genes expression significantly up-regulated 5- and 4.5-fold, respectively, following recovery period in “Fishomi”. Overall, the results suggested that FADs and BGLC could be involved in the increasing of freezing tolerance in olive cultivars, particularly in plants recovery from freezing stress.