The Casparian strip in the root endodermis forms an apoplastic barrier between vascular tissues and outer ground tissues to enforce selective absorption of water and nutrients. Because of its cell-type specificity, the presence of a Casparian strip is used as a marker for a functional endodermis. Here, we examine the minimal regulators required for reprograming non-endodermal cells to build a functional Casparian strip. We demonstrate that the transcription factor SHORT-ROOT (SHR) serves as a master regulator and promotes Casparian strip formation through two independent activities: inducing the expression of essential Casparian strip enzymes via MYB36 and directing the subcellular localization of Casparian strip formation via SCARECROW (SCR). However, this hierarchical signaling cascade still needs SHR-independent small peptides, derived from the stele, to eventually build a functional Casparian strip in non-endodermal cells. Our study provides a synthetic approach to induce Casparian-strip-containing endodermis using a minimal network of regulators and reveals the deployment of both apoplastic and symplastic communication in the promotion of a specific cell fate.

Summary In Arabidopsis , the initiation and proliferation of stomatal lineage cells is controlled by SPEECHLESS ( SPCH ). Phosphorylation of SPCH at the post‐translational level has been reported to regulate stomatal development. Here we report that IDD 16 acts as a negative regulator for stomatal initiation by directly regulating SPCH transcription. In Arabidopsis , IDD 16 overexpression decreased abaxial stomatal density in a dose‐dependent manner. Time course analysis revealed that the initiation of stomatal precursor cells in the IDD 16 ‐ OE plants was severely inhibited. Consistent with these findings, the transcription of SPCH was greatly repressed in the IDD 16 ‐ OE plants. In contrast, IDD 16‐ RNA i transgenic line resulted in enhanced stomatal density, suggesting that IDD 16 is an intrinsic regulator of stomatal development. Ch IP analysis indicated that IDD 16 could directly bind to the SPCH promoter. Furthermore, Arabidopsis plants overexpressing IDD 16 exhibited significantly increased drought tolerance and higher integrated water use efficiency ( WUE ) due to reduction in leaf transpiration. Collectively, our results established that IDD 16 negatively regulates stomatal initiation via trans‐repression of SPCH , and thus provide a practical tool for increasing plant WUE through the manipulation of IDD 16 expression.