There are several advantages to using constitutive promoters in expression vectors used in plant biotechnology, such as:
- High level of production of proteins used to select transgenic cells or plants;
- High level of expression of reporter proteins or scorable markers, allowing easy detection and quantification;
- High level of production of a transcription factor that is part of a regulatory transcription system;
- Production of compounds that requires ubiquitous activity in the plant; and
- Production of compounds that are required during all stages of plant development
The first constitutive promoters used for the expression of transgenes in plants were isolated from plant pathogens.
The search for other constitutive promoters has continued, especially to identify control regions that are able to drive expression of transgenes in monocots. In some monocots such as cereals, it has been found that sequences present in 5′ untranslated transcribed regions (e.g., introns) of certain structural genes are essential for efficient gene expression. Thus, promoters that work well in dicots, which lack introns, do not generally work well in monocots. For this reason, regulatory sequences from monocots have also been identified and cloned into vectors for control of transgene expression. The following constitutive promoters are among the most widely used nowadays and are the ones analyzed in this report.