4. Conclusions 
Due to the economic importance of oil palm (Elaeis guineensis), many studies have been carried out to evaluate the expression profiles of FA and TAG assembly genes in the mesocarp. Limited sequence data exists in public databases, with only recently published details on mesocarp gene expression in oil palm by Tranbarger et al. [6], Bourgis et al. [4], Dussert et al. [5] and Singh et al. [8]. In the present study, we sampled the same palms at different stages of fruit development to reduce biological variation, with all palms being sibling or half-siblings. By developing a mesocarp oil palm microarray, we demonstrate an alternative to the study of gene expression profile in oil palm mesocarp through sequencing. 
This study reports the first development of a 105K (3 × 60 bp probe per isotig) oligonucleotide microarray for oil palm mesocarp gene expression studies. This microarray is an important tool to capture overall gene expression changes in oil palm mesocarp tissue throughout its developmental and maturation stages. The oil palm mesocarp gene expression array was found to be far superior to the Agilent Arabidopsis and rice gene expression array, in terms of signal produced and dynamic signal range. The signals produced using the same RNA samples were generally greater with the probes of the oil palm mesocarp microarray compared to probes of Arabidopsis and rice microarray, as would be expected, despite a likely functional conservation of genes involved in oil biosynthesis between species. Our qPCR validation of the results from the oil palm microarray show good correlation with most of the cases studied and this adds weight to the robustness of this microarray in future oil palm research. Within oil palm expression, the trends of targeted FA genes that were revealed using the microarray show reasonable similarity when compared to published, transcriptome sequencing studies, although some differences were noted. We believe the use of this oil palm mesocarp microarray provides opportunities to further understand the biological changes in the mesocarp tissue during development, especially transcriptional changes during oil development in different germplasm. It can also be used to identify the key regulators and genes that drive the genetic improvement of yield in oil palm. The lower cost of the array approach potentially allows larger populations with more biological replicates to be analyzed and, given the highly heterozygous and heterogeneous nature of oil palm, this is an important consideration.
Figure 7  Expression trend comparison between microarray and qPCR of selected gene candidates throughout mesocarp development.