A diffusible small-RNA-based Turing system dynamically coordinates organ polarity.

The formation of a flat and thin leaf presents a developmentally challenging problem, requiring intricate regulation of adaxial-abaxial (top-bottom) polarity. The patterning principles controlling the spatial arrangement of these domains during organ growth have remained unclear. Here we show that this regulation in Arabidopsis thaliana is achieved by an organ-autonomous Turing reaction-diffusion system centred on mobile small RNAs.

microRNA165 and 166 modulate response of the Arabidopsis root apical meristem to salt stress.

In plants, developmental plasticity allows for the modulation of organ growth in response to environmental cues. Being in contact with soil, roots are the first organ that responds to various types of soil abiotic stress such as high salt concentration. In the root, developmental plasticity relies on changes in the activity of the apical meristem, the region at the tip of the root where a set of self-renewing undifferentiated stem cells sustain growth.

Computational modeling and quantitative physiology reveal central parameters for brassinosteroid-regulated early cell physiological processes linked to elongation growth of the root.

Brassinosteroids (BR) are key hormonal regulators of plant development. However, whereas the individual components of BR perception and signaling are well characterized experimentally, the question of how they can act and whether they are sufficient to carry out the critical function of cellular elongation remains open. Here, we combined computational modeling with quantitative cell physiology to understand the dynamics of the plasma membrane (PM)-localized BR response pathway during the initiation of cellular responses in the epidermis of the root tip that are be linked to cell elongation.

Spatiotemporal Developmental Trajectories in the Arabidopsis Root Revealed Using High-Throughput Single-Cell RNA Sequencing.

High-throughput single-cell RNA sequencing (scRNA-seq) is becoming a cornerstone of developmental research, providing unprecedented power in understanding dynamic processes. Here, we present a high-resolution scRNA-seq expression atlas of the Arabidopsis root composed of thousands of independently profiled cells. This atlas provides detailed spatiotemporal information, identifying defining expression features for all major cell types, including the scarce cells of the quiescent center.

A Role for the F-Box Protein HAWAIIAN SKIRT in Plant microRNA Function.

As regulators of gene expression in multicellular organisms, microRNAs (miRNAs) are crucial for growth and development. Although a plethora of factors involved in their biogenesis and action in Arabidopsis () has been described, these processes and their fine-tuning are not fully understood. Here, we used plants expressing an artificial miRNA target mimic (MIM) to screen for negative regulators of miR156.

Positional information by differential endocytosis splits auxin response to drive Arabidopsis root meristem growth.

In the Arabidopsis root meristem, polar auxin transport creates a transcriptional auxin response gradient that peaks at the stem cell niche and gradually decreases as stem cell daughters divide and differentiate [1-3]. The amplitude and extent of this gradient are essential for both stem cell maintenance and root meristem growth [4, 5]. To investigate why expression of some auxin-responsive genes, such as the essential root meristem growth regulator BREVIS RADIX (BRX) [6], deviates from this gradient, we combined experimental and computational approaches.

Cytokinin-facilitated proteolysis of ARABIDOPSIS RESPONSE REGULATOR 2 attenuates signaling output in two-component circuitry.

Cytokinins propagate signals via multiple phosphorelays in a mechanism similar to bacterial two-component systems. In Arabidopsis, signal outputs are determined by the activation state of transcription factors termed type-B Arabidopsis response regulators (ARRs); however, their regulatory mechanisms are largely unknown. In this study, we demonstrate that the proteolysis of ARR2, a type-B ARR, modulates cytokinin signaling outputs.

Spatio-temporal sequence of cross-regulatory events in root meristem growth.

A central question in developmental biology is how multicellular organisms coordinate cell division and differentiation to determine organ size. In Arabidopsis roots, this balance is controlled by cytokinin-induced expression of SHORT HYPOCOTYL 2 (SHY2) in the so-called transition zone of the meristem, where SHY2 negatively regulates auxin response factors (ARFs) by protein-protein interaction. The resulting down-regulation of PIN-FORMED (PIN) auxin efflux carriers is considered the key event in promoting differentiation of meristematic cells.

BRX promotes Arabidopsis shoot growth.

• BREVIS RADIX (BRX) has been identified through a loss-of-function allele in the Umkirch-1 accession in a natural variation screen for Arabidopsis root growth vigor. Physiological and gene expression analyses have suggested that BRX is rate limiting for auxin-responsive gene expression by mediating cross-talk with the brassinosteroid pathway, as impaired root growth and reduced auxin perception of brx can be (partially) rescued by external brassinosteroid application. • Using genetic tools, we show that brx mutants also display significantly reduced cotyledon and leaf growth.

Dynamic, auxin-responsive plasma membrane-to-nucleus movement of Arabidopsis BRX.

In Arabidopsis, interplay between nuclear auxin perception and trans-cellular polar auxin transport determines the transcriptional auxin response. In brevis radix (brx) mutants, this response is impaired, probably indirectly because of disturbed crosstalk between the auxin and brassinosteroid pathways. Here we provide evidence that BRX protein is plasma membrane-associated, but translocates to the nucleus upon auxin treatment to modulate cellular growth, possibly in conjunction with NGATHA class B3 domain-type transcription factors.

Cytokinins determine Arabidopsis root-meristem size by controlling cell differentiation.

Plant postembryonic development takes place in the meristems, where stem cells self-renew and produce daughter cells that differentiate and give rise to different organ structures. For the maintenance of meristems, the rate of differentiation of daughter cells must equal the generation of new cells: How this is achieved is a central question in plant development. In the Arabidopsis root meristem, stem cells surround a small group of organizing cells, the quiescent center.