Analysis of fatty acid compositions and differential gene expression in two Iranian olive cultivars during fruit ripening

Olive is one of the important oil-produce fruit species with long history of cultivation. Despite high economic importance of olive, the molecular mechanisms that are involved in the oil production were not investigated completely in this fruit crop. In this study, the trend of oil accumulation, its composition and the transcriptional profiles of two important olive cultivars of Iran (‘Mari’ and ‘Shenge’) was screened during different fruit developmental stages (60, 90, 120, 150 and 180 days after flowering [DAF]). These cultivars showed the same trend for oil accumulation but a quite different fatty acid composition during the growing season. According to results, 60–120 DAF was identified as the most critical stages for oil biosynthesis in these olive cultivars. A cDNA-AFLP procedure was employed to detect the transcripts with differential expression during the critical stages of fatty acid biosynthesis in the fruit mesocarp. Altogether 195 distinguished fragments were identified as the transcripts with differential expression in these cultivars during the stages that were mostly important for oil biosynthesis. Out of which, twenty high quality clear transcript-derived fragments (TDFs) were cloned, sequenced and subjected to homology search analysis in GenBank database. Based on the homology search results, the entire differentially expressed TDFs in current investigation were classified into four main categories including oil production, carbohydrate metabolism, defense responsive and signaling related transcripts. Altogether, the majority of TDFs that were involved in the fatty acid biosynthesis and carbohydrate metabolism had higher expression in ‘Mari’, the cultivar which is superior in oil percentage and its composition. The expression of these TDFs coincided with the critical stages of oil accumulation (60–120 DAF). On the contrary, most of the defense related TDFs had higher expression in ‘Shenge’, an olive cultivar which is highly tolerant to the environmental stresses but inferior in the oil percentage and its composition. In conclusion, our finding provided primary information about the molecular basis of oil production in olive mesocarp and revealed new insight into the mechanisms that may be involved in the stress resistance in this fruit crop and shed some light on the probable candidate transcripts that may contribute to these two processes.