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.

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Root stem cell niche (SCN) consists of a quiescent center (QC) and surrounding stem cells. Disrupted symplastic communication leads to loss of stemness in the whole SCN. Several SCN regulators were reported to move between cells for SCN maintenance. However, single mutant of these regulators is insufficient to abolish QC stemness despite the high differentiation rate in surrounding stem cells. To dissect the mechanism behind such distinct stemness in SCN, we combined the mis‐expression strategy with pWOX5:icals3m system in which QC is symplastically isolated. We found the starch accumulation in QC could be synergistically repressed by WUSCHEL‐RELATED HOMEOBOX 5 (WOX5), SHORT‐ROOT (SHR), SCARCROW (SCR), and PLETHORA (PLT). Like PLTs, other core regulators also exhibited dimorphic functions by inhibiting differentiation at a higher dose while promoting cell division at a low protein level. Being located in the center of the intersected expression zones, QC cells receive the highest level of core regulators, forming the most robust stemness within SCN. WUSCHEL‐RELATED HOMEOBOX 5 was sufficient to activate PLT1/2 expression, contributing to the QC‐enriched PLTs. Our results provide experimental evidence supporting the long‐standing hypothesis that the combination of spatial expression, synergistic function and dosage effect of core regulators result in spatially distinct stemness in SCN.

The stem cell niche (SCN) is critical in maintaining continuous postembryonic growth of the plant root. During their growth in soil, plant roots are often challenged by various biotic or abiotic stresses, resulting in damage to the SCN. This can be repaired by the reconstruction of a functional SCN. Previous studies examining the SCN’s reconstruction often introduce physical damage including laser ablation or surgical excision. In this study, we performed a time-course observation of the SCN reconstruction in pWOX5:icals3m roots, an inducible system that causes non-invasive SCN differentiation upon induction of estradiol on Arabidopsis (Arabidopsis thaliana) root. We found a stage-dependent reconstruction of SCN in pWOX5:icals3m roots, with division-driven anatomic reorganization in the early stage of the SCN recovery, and cell fate specification of new SCN in later stages. During the recovery of the SCN, the local accumulation of auxin was coincident with the cell division pattern, exhibiting a spatial shift in the root tip. In the early stage, division mostly occurred in the neighboring stele to the SCN position, while division in endodermal layers seemed to contribute more in the later stages, when the SCN was specified. The precise re-positioning of SCN seemed to be determined by mutual antagonism between auxin and cytokinin, a conserved mechanism that also regulates damage-induced root regeneration. Our results thus provide time-course information about the reconstruction of SCN in intact Arabidopsis roots, which highlights the stage-dependent re-patterning in response to differentiated quiescent center.

Roots are the main organs through which plants absorb water and nutrients. As the key phytohormone involved in root growth, auxin functions in plant environmental responses by modulating auxin synthesis, distribution and polar transport. The Arabidopsis thaliana trehalose-6-phosphate phosphatase gene AtTPPI can improve root architecture, and tppi1 mutants have significantly shortened primary roots. However, the mechanism underlying the short roots of the tppi1 mutant and the upstream signaling pathway and downstream genes regulated by AtTPPI are unclear. Here, we demonstrated that the AtTPPI gene could promote auxin accumulation in AtTPPI-overexpressing plants. By comparing the transcriptomic data of tppi1 and wild-type roots, we found several upregulations of auxin-related genes, including GH3.3, GH3.9 and GH3.12, may play an important role in the AtTPPI gene-mediated auxin transport signaling pathway, ultimately leading to changes in auxin content and primary root length. Moreover, increased AtTPPI expression can regulate primary root growth and lateral root elongation under different concentration of nitrate conditions. Overall, constitutive expression of AtTPPI increased auxin contents and improved lateral root elongation, constituting a new method for improving the nitrogen utilization efficiency of plants.