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In tomato roots, the exodermis forms a genetically distinct polar lignin cap (PLC) barrier from the Casparian strip. SlSCZ and SlEXO1 repress PLC deposition in inner layers. The PLC cannot fully compensate for the CS as a mineral ion barrier.

In an Arabidopsis model, repression of cytokinin in the root meristem produces a distinct population of xylem-pole endodermal cells, which resist suberization to become passage cells that enable transport across the otherwise-impermeable endodermis.

By comparing signalling of two receptor pathways in the same cell-type, the study describes maintenance of signalling specificity at a single-cell level and the role of MAPK networks in this process.

CRISPR activation enables multiplexed, cell-type-specific and stable gene expression in plants. Houbaert et al. successfully reprogrammed gene expression in the root endodermis and restored flavonoid production in mutants, displaying the power of this synthetic biology tool.

This study demonstrates that cryo nanoscale secondary ion mass spectrometry (CryoNanoSIMS) enables direct multi-elemental imaging at subcellular resolution of macro- and micronutrients or trace elements in plants and may provide insights into the in vivo roles of many transporters.

Plants evolved powerful mechanisms to fight against pathogenic microorganisms. So how can they accept and even favour the presence of growth-promoting fungi or bacteria? Here, the authors show that helpful commensal bacteria can suppress part of the plant innate immune system.

Suberin is a complex hydrophobic biopolymer in the cell wall of various plant cell types, including the young root endodermis. Here, the authors identified two sets of auxin-regulated enzymes that mediate suberin biosynthesis and remodelling in the differentiated root endodermis in Arabidopsis.

Suberizing plant cells export suberin monomers outside of the cell to form a hydrophobic barrier. Here the authors propose a role for extracellular vesiculo-tubular structures in the deposition of suberin monomers.

Casparian strips are extracellular diffusion barriers in plant roots. Here, Barbosa et al. provide evidence that CASP proteins shape Casparian strips by displacing vesicle tethering factors and organizing cell wall formation

A new screen for Arabidopsis defective in Casparian strip formation identifies EXO70A1 as a central player. This subunit of the exocyst complex is needed for correct ring-like CASP1 localization, but its role is uncoupled from secretion.

The Casparian strip (CS) is a hydrophobic endodermal barrier isolating the cortex from the vasculature in the roots. A visual genetic screen identifies SCHENGEN1, a novel receptor-like kinase crucial for the integrity and positioning of the CS.

The closest homologue of GNOM in Arabidopsis thaliana, GNOM-LIKE1 (GNL1) performs the regulation of endoplasmic reticulum–Golgi transport in plants.

GNL1 localizes to and acts primarily at Golgi stacks, regulating COPI-coated vesicle formation. GNOM can functionally substitute for GNL1, but not vice versa. Hence the ARF–GEFs of the GBF1 class perform a conserved role in the endoplasmic reticulum–Golgi trafficking which is done by GNOM and GNL1 in plants

Microorganism-associated molecular patterns such as flagellin lead to suppression of root iron acquisition through localized degradation of the systemic iron-deficiency signalling peptide Iron Man 1 in Arabidopsis thaliana.

Plant roots can respond to the environment by modifying cell type development. Here, the molecular pathways controlling root exodermal suberin are defined, as is its role in drought response. Modulating exodermal suberin levels can be a target for improved plant environmental resilience.

The NOPE1 gene is required for arbuscular mycorrhizal symbiosis in maize. The causal gene is now identified using rice. It is the first identified GlcNAc transporter in plants, needed for presymbiotic fungal reprogramming.

Defects in the Casparian strip, a fine band of lignin that seals root endodermal cells and plays roles in nutrient homeostasis, activate a signaling pathway leading to over-lignification. Here, the authors show that this process leads to the deposition of compensatory lignin that is chemically distinct from Casparian strip lignin.

How can cells differentiate into different types? Here, the authors identify the minimal requirement (the SHR transcription factor and the CIF2 peptide) in Arabidopsis roots to transform an epidermis cell into an endodermis cell.

Lateral root development is dependent on precise control of the distribution of the plant hormone auxin. Here Chen et al. propose the transcription factors ARF7 and FLP participate in a feed forward motif to mediate expression of the auxin transporter PIN3and consequently regulate lateral root development.

Ubiquitination of cargo proteins regulates endocytosis in yeast and mammalian cells, however the extent to which this applies to plants is less clear. Martins et al. show that both internalization and vacuolar targetting of the Arabidopsisbrassinosteroid receptor BRI1 are regulated by ubiquitination.

Here the authors discuss the use of synthetic communities, or SynComs, in plant–microbiome research and propose steps to develop community standards that will support future research.

Jürgens and colleagues show that the ARF GEFs GNOM and GNL2 have essential roles in polarized cell growth of root hairs and pollen, respectively. Their findings support an important function for endosomal recycling, rather than polarized secretion, in the targeted delivery of proteins necessary for polar tip growth.

The polar transport of the plant hormone auxin is dependent on the localization of its efflux carriers called PINs, but the mechanism mediating polarity of PIN proteins within cells remains unclear. This study suggests a two-step mechanism generating PIN polarity. PINs are first targeted to the plasma membrane in a non-polar manner, and polarity is established in subsequent step involving internalization and recycling. Interference with endocytosis results in the loss of PIN polarity leading to a perturbation in auxin gradients.