A single cis-element that controls cell-type specific expression in Arabidopsis

In multicellular organisms the specification of distinct tissues within organs allows compartmentation of complex processes. However, the mechanisms that allow gene expression to be restricted to such tissues are poorly understood. To better understand this process, we focused on bundle sheath expression of the gene encoding the MYB76 transcription factor in Arabidopsis thaliana. Functional and computational analyses were combined to identify a seven-nucleotide motif within a DNaseI hypersensitive site in the MYB76 promoter that is necessary and sufficient to direct gene expression to bundle sheath cells. Thus, combining information from DNaseI hypersensitivity assays with classical truncation analysis allowed the rapid identification of a single cis-element that governs cell type-specificity. This motif is conserved in the Brassicaceae, acts to positively regulate gene expression, and is recognised in planta by two DREB transcription factors. In contrast to previous studies, these data indicate that the patterning of gene expression to specific cell types can be mediated by relatively simple interactions between cis-elements and transcription factors. Moreover, as the element in the MYB76 promoter is short and can be oligomerized to tune expression levels it is well-suited for use in synthetic biology applications that require tissue specific expression in plants.