Single nucleotide polymorphisms in oil palm HOMOGENTISATE GERANYL-GERANYL TRANSFERASE promoter for species differentiation and TOCOTRIENOL improvement

Abstract

High level of variability in the palm oil vitamin E content was observed in the Elaeis guineensis and Elaeis oleifera germplasm materials. Homogentisate geranylgeranyl transferase (HGGT) is an important vitamin E biosynthetic enzyme that catalyzes the first committed step for tocotrienol biosynthesis. This study aimed to identify the SNPs in the promoter of oil palm HGGT that associate with the high vitamin E trait. Species-specific mismatch primer within ACGT promoter motif successfully differentiated E. guineensis from E. oleifera palms harboring ATGT. However, these primers could not differentiate the high from the low vitamin E palms in the Angolan and Tanzanian populations of E. guineensis. Sequence alignment showed the presence of a SNP (−454) that associate with high vitamin E Angolan (AH) and Tanzanian (TH) palms and two SNPs, −781 and − 113 unique to AH. Functional characterization to determine the roles of SNPs in influencing E. guineensis HGGT (EgHGGT) promoter activity was carried out by transient β-glucuronidase (GUS) reporter gene assay in mesocarp tissues for comparing activities of promoters from commercial E. guineensis (COM), AH, TH and a mutant derivative of COM (CM) produced by introducing the variant found in common in AH and TH. AH promoter gave significantly higher GUS activity than TH while COM and CM gave the lowest. We suggest that the CAAT-box unique to AH at the SNP (−113), a well-known proximal promoter element may enhance EgHGGT promoter activity resulting in the significantly higher α-tocotrienol content in AH, leading to the higher overall tocotrienol level.