1. Introduction
Oil palm is one of the most productive oil crops with average oil yields of 4.2 tons of oil per hectare annually in Malaysia compared to other major world oil crops such as rapeseed and soybean with 1.2 and 0.4 tons per hectare, respectively [1,2]. Oil palm mesocarp tissue can accumulate up to 90% of its dry weight as oil at maturity, the highest known level of accumulation in the plant kingdom [3,4]. With the increase in global vegetable oil consumption, yield-related traits are the key target for plant breeders. Due to its economic importance, extensive research has focused on deciphering the underlying mechanisms and pathways influencing the efficient oil production machinery in the oil palm mesocarp tissue [3,4,5,6,7,8].
Recently, high throughput approaches, including transcriptome sequencing and microarray analysis, have been adopted to study trait-related pathways and provide an in-depth knowledge of the underlying mechanisms involved in oil production, drought, disease tolerance, and tissue development among others. These approaches have been adopted in both plants and animals [4,6,9,10,11,12,13,14,15]. Microarrays have been widely used due to their efficiency for analyzing global patterns of expression in a single experiment [16]. Currently, microarray analysis is still cheaper than comparative analysis methods using transcriptome sequencing (e.g., RNAseq), especially when large numbers of samples are being evaluated. However, commercially available and well annotated microarrays for plants are limited to several model and major crop species. Due to this limited availability, one approach has been to cross-hybridize RNA samples on microarrays from other plant species [17,18]. The success of cross-hybridization microarray experiments relies largely on the hybridization efficiency of the target genome to the cross-species probe sequences. The accuracy of gene expression measurements will also depend on the evolutionary distance between the target and the microarray design plant species, as well as the relative rate of evolution within the classes of genes under evaluation.