Olive (Olea europaea) cv.Chondrolia Chalkidikis: Control vs NaCl-treated

A comparative transcriptomics approach was used as a tool to unravel gene regulatory networks underlying salinity response in olive trees by simulating as much as possible olive growing conditions in the field. Specifically, we investigated the genotype-dependent differences in the transcriptome response of two olive cultivars, a salt tolerant and a salt sensitive. A 135 day long comparative salinity experiment was conducted using one year old trees exposed to NaCl stress for 90 days followed by 45 days of post-stress period. Total RNA was extracted from the root samples after 15, 45 and 90 days of NaCl-treated and un-treated olive trees as well as after 15 and 45 days of post-treatment period and used for microarray hybridizations using a loop design. Hierarchical clustering of differentially expressed transcripts revealed two major, distinct clusters for each cultivar. Despite the limited number of probe set, transcriptional regulatory networks were constructed for the salt-tolerant and salt-sensitive cultivar. The comparison of the salt responsive transcriptional regulatory networks in olive with those reported for Arabidopsis suggests that a tree species might respond in a similar to Arabidopsis way at the transcriptome level under salinity stress. Five experimental time-points were analyzed: 15days stress, 45days stress, 90days stress, 15days post-stress and 45days post-stress. In each timepoint treated and untreated (control) samples were obtained. Dye swap hybridizations and 4 biological replicates were performed for each treatment/timepoint in a loop design experimental setup. Each sample included three spot replicates.