Differential expression of fatty acid desaturases in Mari and Shengeh olive cultivars during fruit development and ripening

To understand the molecular basis of the higher oleic/linoleic acid content in Mari and Koroneiki with respect to Shengeh and Arbequina olive cultivars, we have focused on analysis of fatty acids, as well as expression levels of OeSAD and three oleate desaturase genes during fruit development and ripening. The mesocarp oil content was determined using a Minispec NMR. Moreover, oleic and linoleic acid contents were recorded by GC. Quantitative real time PCR was used for gene expression analysis. Mari and Shengeh exhibited the highest and lowest levels of OeSAD gene expression, respectively, which corresponded fully to a change in the pattern of oleic acid and oil accumulation throughout mesocarp development. Regarding oleate desaturases, a decreasing pattern of OeFAD2-1 and OeFAD6 transcripts accompanied by an increasing trend of OeFAD2-2 expression during mesocarp development showed that, coinciding with oil accumulation, linoleic acid content is mainly determined by the OeFAD2-2 gene. In conclusion, the higher oleic/linoleic ratio in Mari and Koroneiki cultivars compared to Shengeh and Arbequina was due to much higher expression levels of OeSAD and lower expression levels of OeFAD2-2. Practical applications: Increasing the oleic to linoleic acid ratio has become one of the major goals for researchers in the area of plant lipid modification. To this end, understanding the mechanisms by which fatty acid composition is determined during olive fruit development and ripening would represent an important step toward the ultimate goal of regulating these processes in a directed and predictable manner. Relative expression of OeSAD gene (B) during mesocarp development and ripening of the high (Mari and Koroneiki) and low (Shengeh and Arbequina) oleic acid olive cultivars. The beginning of fruit ripening, corresponding to the appearance of pink-purple color, is marked by an arrow. Different letterings show that the results significantly different at P < 0.05. The bars represent the SD of the mean (DAFB, days after full bloom).

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