Regulatory Mechanisms Underlying Oil Palm Fruit Mesocarp Maturation, Ripening, and Functional Specialization in Lipid and Carotenoid Metabolism    

Abstract

Fruit provide essential nutrients and vitamins for the human diet. Not only is the lipid-rich fleshy mesocarp tissue of the oil palm (Elaeis guineensis) fruit the main source of edible oil for the world, but it is also the richest dietary source of provitamin A. This study examines the transcriptional basis of these two outstanding metabolic characters in the oil palm mesocarp. Morphological, cellular, biochemical, and hormonal features defined key phases of mesocarp development. A 454 pyrosequencingderived transcriptome was then assembled for the developmental phases preceding and during maturation and ripening, when high rates of lipid and carotenoid biosynthesis occur. A total of 2,629 contigs with differential representation revealed coordination of metabolic and regulatory components. Further analysis focused on the fatty acid and triacylglycerol assembly pathways and during carotenogenesis. Notably, a contig similar to the Arabidopsis (Arabidopsis thaliana) seed oil transcription factor WRINKLED1 was identified with a transcript profile coordinated with those of several fatty acid biosynthetic genes and the high rates of lipid accumulation, suggesting some common regulatory features between seeds and fruits. We also focused on transcriptional regulatory networks of the fruit, in particular those related to ethylene transcriptional and GLOBOSA/PISTILLATA-like proteins in the mesocarp and a central role for ethylene-coordinated transcriptional regulation of type VII ethylene response factors during ripening. Our results suggest that divergence has occurred in the regulatory components in this monocot fruit compared with those identified in the dicot tomato (Solanum lycopersicum) fleshy fruit model.

Compartmentation of Triacylglycerol Accumulation in Plants

“…Transcriptional profiling of oil palm mesocarp revealed Ͼ50-fold higher WRI1 expression levels compared with date palm mesocarp, a closely related species that contains no oil (13). Consistent with data in developing seeds (14), genes encoding machinery for FA biosynthesis and pyruvate supply are up-regulated substantially in oil palm (an average of Ͼ13-fold) (15). The direct precursor of carbon for FA synthesis is pyruvate in most oil-synthesizing tissues, and a plastidial pyruvate dehydrogenase (PDH) supplies acetyl-CoA for ACCase.…”

Quantitative trait loci (QTLs) analysis of palm oil fatty acid composition in an interspecific pseudo-backcross from Elaeis oleifera (H.B.K.) Cortés and oil palm (Elaeis guineensis Jacq.)

“…In our full-length Elaeis cDNA libraries, the number of distinct expressed copies for our five genes KAS I, KAS II, SAD, FATA, and FATB were in accordance with the cDNA data published in E. guineensis by Bourgis et al (2011) and Tranbarger et al (2011). They were proved as distinct by mapping (different loci and not allelic variants).…”

“…We used the Blast2GO pipeline (Götz et al 2008) to annotate the contigs with the Gene Ontology terms based on our BLAST results. Also, a BLAST analysis was performed with the E. guineensis cDNA libraries of Bourgis et al (2011) and Tranbarger et al (2011). We used the Prot4EST pipeline (Wasmuth and Blaxter 2004) to obtain a protein prediction from our contig sequences.…”

“…More recently, AlShanfari et al (2011) constructed a suppression subtractive hybridization (SSH) library to identify genes involved in fruit ripening in E. guineensis. Bourgis et al (2011) and Tranbarger et al (2011) notably analyzed the gene expression and regulatory mechanisms underlying the fatty acid biosynthesis during the oil palm fruit mesocarp maturation and ripening. Singh et al (2009) identified quantitative trait loci (QTLs) for fatty acid composition using 81 individuals of an Elaeis interspecific cross.…”

Using modern plant breeding to improve the nutritional and technological qualities of oil crops

“…In many ways transcriptome sequences can be much more useful than genome sequences because they only include the particular fraction of the tens of thousands of genes that are expressed under specific conditions. In the case of oil palm, the analysis of the fruit transcriptome during oil accumulation is already proving very useful in identifying key genes that may regulate this vital process (Bourgis et al, 2011;Dussert et al, 2013;Tranbarger et al, 2011).…”