A SNP variation in an expansin (EgExp4) gene affects height in oil palm

Oil palm (Elaeis guineensis Jacq.), an Aracaceae family plant, is utilized for both consumable and non-consumable products, including cooking oil, cosmetics and biodiesel production. Oil palm is a perennial tree with 25 years of optimal harvesting time and a height of up to 18 m. However, harvesting of oil palm fruit bunches with heights of more than 2-3 meters is challenging for oil palm farmers. Thus, understanding the genetic control of height would be beneficial for using gene-based markers to speed up oil palm breeding programs to select semi-dwarf oil palm varieties. This study aims to identify Insertion/Deletions (InDels) and single nucleotide polymorphisms (SNPs) of five height-related genes, including EgDELLA1, EgGRF1, EgGA20ox1, EgAPG1 and EgExp4, in short and tall oil palm groups by PacBio SMRT sequencing technology. Then, the SNP variation's association with height was validated in the Golden Tenera (GT) population. All targeted genes were successfully amplified by two rounds of PCR amplification with expected sizes that ranged from 2,516 to 3,015 base pair (bp), covering 5' UTR, gene sequences and 3' UTR from 20 short and 20 tall oil palm trees. As a result, 1,166, 909, 1,494, 387 and 5,384 full-length genomic DNA sequences were revealed by PacBio SMRT sequencing technology, from EgDELLA1, EgGRF1, EgGA20ox1, EgAPG1 and EgExp4 genes, respectively. Twelve variations, including eight InDels and four SNPs, were identified from EgDELLA1, EgGRF1, EgGA20ox1 and EgExp4. No variation was found for EgAPG1. After SNP through-put genotyping of 4 targeted SNP markers was done by PACE™ SNP genotyping, the association with height was determined in the GT population. Only the mEgExp4_SNP118 marker, designed from EgExp4 gene, was found to associate with height in 2 of 4 height-recordings, with p values of 0.0383 for height (HT)-1 and 0.0263 for HT-4. In conclusion, this marker is a potential gene-based marker that may be used in oil palm breeding programs for selecting semi-dwarf oil palm varieties in the near future.