A conserved mechanism determines the activity of two pivotal transcription factors that control epidermal cell differentiation in Arabidopsis thaliana

Abstract

The surface of plants is covered by the epidermis, which protects the plant’s body from the external environment and mediates inter-cell layer signaling to regulate plant development. Therefore, the manifestation of epidermal traits at a precise location is a prerequisite for their normal growth and development. In Arabidopsis thaliana, class IV homeodomain-leucine zipper transcription factors PROTODERMAL FACTOR2 (PDF2) and ARABIDOPSIS THALIANA MERISTEM LAYER1 (ATML1) play redundant roles in epidermal cell differentiation. Nevertheless, several pieces of evidence suggest that the activity and/or function of PDF2 and ATML1 are regulated differently. The role of the steroidogenic acute regulatory protein-related lipid transfer (START) domain of ATML1 in restricting this protein’s activity has been demonstrated; however, whether this lipid-dependent mechanism regulates PDF2 expression is unknown. In this study, we demonstrated that the START domains of PDF2 and ATML1, regulate protein turnover in a position-dependent manner and affect the dimeric proteins. Our results show that a conserved mechanism provides the basis for the functional redundancy of PDF2 and ATML1 in epidermal cell differentiation and that an unidentified regulatory layer specific to PDF2 or ATML1 is responsible for the difference in the activity and/or function of PDF2 and ATML1.

Quantitative Modeling of the Short-Term Response to Nitrogen Availability that Coordinates Early Events in Lateral Root Initiation

“…LBD13 regulates the number of emerged lateral roots per cm primary root (Figure 5C); ERF107 regulates lateral root length (Figure 4C) and PDF2 has been shown to function in lateral root development prior to emergence. 47,48…”

“…We modeled LBD13 expression in a time-dependent manner based on the single cell expression data. In addition, we included the homodimerization of PDF2 48 , which led to a better fit of the model to the expression dynamics of its downstream target ERF107 as observed in the cell-type specific single cell expression data. When modeling a FFL, the two regulators, here LBD13 and PDF2, can act through an OR gate or an AND gate, where only LBD13 or PDF2 would need to be expressed to activate ERF107; or where both TFs need to be expressed to activate ERF107, respectively.…”

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

“…Our findings suggest that the transcription factor ATML1 plays a key role in this feedback loop by activating the biosynthesis of (V)LCFAs, which are incorporated into lipid ligands of ATML1. Previous research has suggested that START domains in ATML1 and related HD-ZIP transcription factors bind to (V)LCFA-containing lipids ( 32 , 33 ). Using AlphaFold protein structure prediction, we found that ATML1 contains two adjacent START domains, not just one as previously thought.…”

“…Phospholipids and sphingolipids, such as PC, and ceramide (Cer), are among the primary ligands for the START domain that are thought to be common to plant and animal systems (25,(29)(30)(31). Recent studies in plants showed that the START domain of ATML1 can bind to ceramides and restrict its expression to the epidermis (32,33). The START domains in PDF2 and PHABULOSA (PHB, a class III HD-ZIP) bind to the phospholipids lysophosphatidylcholine (LysoPC) and PC, respectively, to regulate target gene transcription (29,30).…”

HD-ZIP Transcription Factors and Brassinosteroid Signaling Play a Role in Capitulum Patterning in Chrysanthemum

“…However, PDF2 and its close homolog ARABIDOPSIS THALIANA MERISTEM LAYER1 (ATML1) are also redundantly regulating epidermal cell differentiation in Arabidopsis [53][54][55]. The epidermal cell layer is the outermost cell layer of most tissues, usually covered with a cuticle and acting as a defensive layer against biotic and abiotic threats [56]. The downregulation of PDF2/ATML1-like genes in both mutants may thus also explain the strong overrepresentation of the GO term 'cutin biosynthesis' in both RNA-seq experiments.…”