5' Regulatory region of ubiquitin 2 gene from Porteresia coarctata makes efficient promoters for transgene expression in monocots and dicots.

KEY MESSAGE: Porteresia ubiquitin 5' regulatory region drives transgene expression in monocots and dicots. Ubiquitin promoters are promising candidates for constitutive transgene expression in plants. In this study, we isolated and characterized a novel 5' regulatory sequence of a ubiquitin gene from Porteresia coarctata, a stress-tolerant wild grass species. Through functional analysis in heterologous plant systems, we have demonstrated that full length (Port Ubi2.3) or truncated sequence (PD2) of the isolated regulatory fragment can drive constitutive expression of GUS in monocots and/or dicots. In silico analysis of Port Ubi2.3 has revealed the presence of a 640 bp core promoter region followed by two exons and two introns with numerous putative cis-acting sites scattered throughout the regulatory region. Transformation and expression studies of six different deletion constructs in rice, tobacco and sugarcane revealed that the proximal intron has an enhancing effect on the activity of the core promoter in both monocots and dicots, whereas, Port Ubi2.3 was able to render strong expression only in monocots. This regulatory sequence is quite distinct from the other reported ubiquitin promoters in structure and performs better in monocots compared to other commonly used promoters-maize Ubi1 and Cauliflower Mosaic Virus 35S.