ISOLATION OF AN OIL PALM CONSTITUTIVE PROMOTER DERIVED FROM UBIQUITIN EXTENSION PROTEIN (uep2) GENE

Constitutive promoters are essential component in genetic engineering. The promoters are usually derived from genes that are constitutively expressed or function as housekeeping genes. In this study, the ubiquitin extension protein (uep2) gene was identified as a constitutively expressed gene in oil palm. The 5' region of the oil palm uep2 gene was isolated and the promoter truncation analysis was performed. The full length of uep2 (uep2a) and its truncation derivatives (uep2b and uep2c) were linked to beta-glucuronidase (gus) reporter gene. The strength and the activity of the uep2 promoter were transiently evaluated in various oil palm tissues and tobacco leaves. Histochemical GUS analysis showed that the activity of truncated uep2b promoter was higher than the full length promoter and uep2c derivative in most tissues tested. Result also showed that uep2b was capable of directing the expression of GUS in all tissues with the high activity detected in oil palm embryoid, green leaves, and tobacco leaves. The full length of uep2 (uep2a) promoter also exhibited the ability to direct the expression of GUS in all tissues with the high activity detected in the plantlet stem. By contrast, although the uep2c showed high activity in young leaves and embryoid, a significant decrease of GUS expression was seen in green tissues. These results indicated that the region between position -1096 and -3237 is essential for constitutive transcriptional regulation as deletion of the region resulted in a significant decrease in the promoter activity. Though maize ubi1 and CaMV35S promoters showed a relatively higher activity than uep2, the uep2 has the ability to induce the constitutive GUS expression in all tissues tested. These results showed that 5' flanking region of uep2 gene is active in oil palm and tobacco, suggesting that the promoter could be used as an alternative promoter for driving constitutive expression of transgenes in oil palm and other plants.