Abstract
BackgroundThe oil yield trait of oil palm is expected to involve multiple genes, environmental influences and interactions. Many of the underlying mechanisms that contribute to oil yield are still poorly understood. In this study, we used a microarray approach to study the gene expression profiles of mesocarp tissue at different developmental stages, comparing genetically related high- and low- oil yielding palms to identify genes that contributed to the higher oil-yielding palm and might contribute to the wider genetic improvement of oil palm breeding populations.ResultsA total of 3412 (2001 annotated) gene candidates were found to be significantly differentially expressed between high- and low-yielding palms at at least one of the different stages of mesocarp development evaluated. Gene Ontologies (GO) enrichment analysis identified 28 significantly enriched GO terms, including regulation of transcription, fatty acid biosynthesis and metabolic processes. These differentially expressed genes comprise several transcription factors, such as, bHLH, Dof zinc finger proteins and MADS box proteins. Several genes involved in glycolysis, TCA, and fatty acid biosynthesis pathways were also found up-regulated in high-yielding oil palm, among them; pyruvate dehydrogenase E1 component Subunit Beta (PDH), ATP-citrate lyase, β- ketoacyl-ACP synthases I (KAS I), β- ketoacyl-ACP synthases III (KAS III) and ketoacyl-ACP reductase (KAR). Sucrose metabolism-related genes such as Invertase, Sucrose Synthase 2 and Sucrose Phosphatase 2 were found to be down-regulated in high-yielding oil palms, compared to the lower yield palms.ConclusionsOur findings indicate that a higher carbon flux (channeled through down-regulation of the Sucrose Synthase 2 pathway) was being utilized by up-regulated genes involved in glycolysis, TCA and fatty acid biosynthesis leading to enhanced oil production in the high-yielding oil palm. These findings are an important stepping stone to understand the processes that lead to production of high-yielding oil palms and have implications for breeding to maximize oil production.
Highlights
The oil yield trait of oil palm is expected to involve multiple genes, environmental influences and interactions
They found that the high oil content in oil palm mesocarp is associated with higher transcript levels of enzymes involved in fatty acid biosynthesis, as might be expected, as well as key enzymes from the plastidial carbon metabolism, compared to the gene expression in developing fruits of date palm
Due to sampling palms from the open field and the lack of an applied treatment beyond the natural oil production differences observed, all differentially expressed candidates became statistically insignificant for all the time points analyzed when False Discovery Rate (FDR) was applied (8 samples of HY, 8 samples from LY for 12-20 weeks after pollination (WAP), 6 samples from HY and 7 samples from LY for 22 WAP)
Summary
The oil yield trait of oil palm is expected to involve multiple genes, environmental influences and interactions. Bourgis et al compared the transcriptome and metabolites of oil palm and date palm mesocarp to investigate the mechanistic differences that lead to oil and sugar accumulation, respectively [7] They found that the high oil content in oil palm mesocarp is associated with higher transcript levels of enzymes involved in fatty acid biosynthesis, as might be expected, as well as key enzymes from the plastidial carbon metabolism, compared to the gene expression in developing fruits of date palm. Lauric acid predominates in the endosperm, while palmitic and oleic acid are the main components of oil found in the mesocarp This is of great interest to the palm oil industry as different types of fatty acid have their own applications. Lauric acid is widely used in soap and the cosmetic industry, while mesocarp oil rich in oleic acid is preferable for cooking purposes
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