Functional analysis of the Arabidopsis thaliana MUTE promoter reveals a regulatory region sufficient for stomatal-lineage expression.

Main Conclusion: The MUTE promoter contains a 175-bp region rich in Dof regulatory elements (AAAG) that is necessary and sufficient for initiation of transcription in meristemoids and the stomatal lineage. The molecular mechanism underlying the decision to divide or differentiate is a central question in developmental biology. During stomatal development, expression of the master regulator MUTE triggers the differentiation of meristemoids into stomata. In this study, we carried out MUTE promoter deletion analysis to define a regulatory region that promotes the initiation of expression in meristemoids. Expression constructs with truncated promoter fragments fused to β-glucuronidase (GUS) were developed. The full-length promoter and promoter truncations of at least 500 bp from the translational start site exhibited normal spatiotemporal expression patterns. Further truncation revealed a 175-bp promoter fragment that was necessary and sufficient for stomatal-lineage expression. Known cis-elements were identified and tested for functional relevance. Comparison of orthologous MUTE promoters suggested DNA binding with one finger (Dof) regulatory elements and novel motifs may be important for regulation. Our data highlight the complexity and combinatorial control of gene regulation and provides tools to further investigate the genetic control of stomatal development.