Moontag: An Improved Programmable Transcription Activator for Plants

CRISPR-Cas9 based transcriptional activators have been developed to induce gene expression in eukaryotic and prokaryotic organisms. The main advantages of CRISPR-Cas9 based systems is that they can achieve high levels of transcriptional activation and are very easy to program via pairing between the guide RNA and the DNA target strand. One of these CRISPR-Cas9 systems is SunTag, a second-generation system that activates transcription by recruiting multiple copies of an activation domain (AD) to its target promoters. SunTag has been tested in Arabidopsis showing to be a strong transcriptional activator. However, we found that in the monocot plant Setaria, SunTag was difficult to stably express in transgenic plants. To overcome this problem, we designed MoonTag, a novel activator that works on the same basic principle of SunTag, but whose components are well tolerated when stably expressed in transgenic plants. In Setaria, MoonTag is capable of inducing high levels of transcription of a reporter gene as well as of endogenous genes. More important, MoonTag components are expressed in transgenic plants to high levels without any deleterious effects. MoonTag is also able to efficiently activate genes in eudicotyledonous species such as Arabidopsis and tomato. We further increased the activation potential of MoonTag by replacing VP64, originally used in SunTag, by other ADs from plant origin. Thus, MoonTag represents a novel activator that could be used to regulate the transcription of endogenous genes in many plant species.