Enhancer activation via TCP and HD-ZIP and repression by Dof transcription factors mediate giant cell-specific expression

Abstract

Proper cell-type identity relies on highly coordinated regulation of gene expression. Regulatory elements such as enhancers can produce cell type-specific expression patterns, but the mechanisms underlying specificity are not well understood. We previously identified an enhancer region capable of driving specific expression in giant cells, which are large, highly endoreduplicated cells in the Arabidopsis thaliana sepal epidermis. In this study, we use the giant cell enhancer as a model to understand the regulatory logic that promotes cell type-specific expression. Our dissection of the enhancer revealed that giant cell specificity is mediated primarily through the combination of two activators and one repressor. HD-ZIP and TCP transcription factors are involved in the activation of expression throughout the epidermis. High expression of HD-ZIP transcription factor genes in giant cells promoted higher expression driven by the enhancer in giant cells. Dof transcription factors repressed the activity of the enhancer such that only giant cells have higher expression levels driven by the enhancer. Thus, our data are consistent with a conceptual model whereby cell type-specific expression emerges from the combined activities of three transcription factor families activating and repressing expression in epidermal cells.

The transcription factor ATML1 maintains giant cell identity by inducing synthesis of its own long-chain fatty acid-containing ligands

“…We further tested whether, and to what extent, giant cells lose their identity and de-differentiate by examining the expression of molecular markers specific to giant and small cells ( 12 , 13 , 46 ). Live imaging of ATML1-OX inflorescences containing the giant and small cell markers treated with mock and 300 nM cafenstrole, revealed that in 300 nM cafenstrole, cells started to express the small cell marker basipetally from the sepal tip, compared with mock-treated sepals (Fig.…”

“…Accession Col-0 was used as the wild type accession throughout the experiments, except for in comparison to the cer1-1 , cer3-1 , cer6-2 , and cer6-2R mutants which are in the Landsberg erecta (L er ) background. The small cell (CS70134) and giant cell markers (pAR111) were previously described ( 12 , 46 ).…”

Making a giant: Uncovering gene regulation underlying the formation of giant cells in Arabidopsis sepals

“…Giant cells establish sepal curvature and are involved in plant defense ( Roeder et al 2012 ). In this issue of The Plant Cell , Lilan Hong, Byron Rusnak, Clint S. Ko, and colleagues ( Hong et al 2023 ) uncovered the regulatory mechanism driving cell-specific gene expression during giant cell formation in Arabidopsis sepals. In particular, they dissected the function of a 1 kilobase region previously shown to enhance gene expression in giant cells ( Roeder et al 2012 ).…”