High transgene expression levels in sugarcane ( Saccharum officinarum L.) driven by the rice ubiquitin promoter RUBQ2

Discovery and evaluation of new regulatory elements are urgently needed for future improvements in transgene expression in sugarcane. The rice polyubiquitin promoter RUBQ2 was fused to the β-glucuronidase (GUS) reporter gene and expression levels were monitored after particle bombardment and Agrobacterium-mediated transformation. DNA constructs containing RUBQ2 promoter produced higher levels of transient GUS expression by particle bombardment in calli and leaves compared with control constructs containing the Cauliflower Mosaic Virus 35S (CaMV 35S) promoter or the maize polyubiquitin Ubi-1 promoter. Similarly, the RUBQ2 promoter produced higher levels of transient GUS expression in calli than the Ubi-1 promoter via Agrobacterium-mediated transformation using strains LABA4404 and AGL1. Use of Agrobacterium strain LBA4404 resulted in a 7-fold increase in transient gene expression over strain AGL1. Stably transformed plants were produced via particle bombardment, and stable GUS expression levels by RUBQ2 were increased 1.6-fold over those by Ubi-1, while no GUS expression was detected in the transgenic plants with CaMV 35S promoter. Southern blotting analysis revealed stable, multi-copy GUS gene integration into the sugarcane genome via particle bombardment. Results from this study indicate that RUBQ2 can serve as a new regulatory element to provide high levels of transgene expression in sugarcane.