Transcriptional regulation of oil synthesis and fatty acid desaturation in olive fruit under elevated growth temperature

Ambient temperature during olive fruit growth modulates oil content and fatty acid composition. However, the mechanisms behind their regulation are not completely understood. In this work, the transcriptional regulation of oil synthesis and fatty acid desaturation were evaluated by manipulating air temperature in the field. Three-year-old trees of cultivars 'Arbequina' and 'Coratina' were placed in open-top chambers (OTC) where control or elevated air temperatures were applied early in the oil accumulation phase, and fruits were sampled after 10 or 36 days of exposure. Upon elevated temperature, the oil content in 'Coratina' mesocarp tissue decreased less than in 'Arbequina' compared to their respective controls. However, the oleic acid content of 'Coratina' was more sensitive to temperature. The cultivar-dependent responses were mainly explained by differential gene expression. In 'Arbequina', the downregulation of genes involved in triacylglycerol biosynthesis (OeDGAT1-2, OeDGAT2, OePDAT1-1, and OePDAT1-2), upon elevated temperature explains the decrease in oil content, whereas the downregulation of the fatty acid desaturases genes (OeSAD1, OeSAD3, OeFAD2-1, OeFAD2-2, and OeFAD2-5) decreased the oleic/linoleic ratio. In contrast, in 'Coratina', OePDAT1-2 downregulation explains the fluctuation in oil content, but the increased expression of three members of the OeFAD2 gene family was responsible for the oleic/linoleic ratio. This knowledge contributes to developing an integrated strategy for olive production under high temperatures, and the analysis of the expression of key genes could be used as a selection criterion in genetic improvement programs for the adaptation of olive cultivars to global warming.