Highlights in gibberellin research: A tale of the dwarf and the slender.

It has been almost a century since biologically active gibberellin (GA) was isolated. Here, we give a historical overview of the early efforts in establishing the GA biosynthesis and catabolism pathway, characterizing the enzymes for GA metabolism, and elucidating their corresponding genes. We then highlight more recent studies that have identified the GA receptors and early GA signaling components (DELLA repressors and F-box activators), determined the molecular mechanism of DELLA-mediated transcription reprograming, and revealed how DELLAs integrate multiple signaling pathways to regulate plant vegetative and reproductive development in response to internal and external cues.

Cytokinin activity - transport and homeostasis at the whole plant, cell, and subcellular levels.

Cytokinins (CKs) are important plant hormones that regulate a variety of biological processes implicated in plant development and stress responses. Here, we summarize the most recent advances in discovering and characterizing the membrane transporters involved in long- and short-distance translocation of CKs and their significance in CK signal activity. We highlight the discovery of PUP7 and PUP21 tonoplast-localized transporters and propose potential mechanisms for CK subcellular homeostasis.

Gibberellin and abscisic acid transporters facilitate endodermal suberin formation in Arabidopsis.

The plant hormone gibberellin (GA) regulates multiple developmental processes. It accumulates in the root elongating endodermis, but how it moves into this cell file and the significance of this accumulation are unclear. Here we identify three NITRATE TRANSPORTER1/PEPTIDE TRANSPORTER (NPF) transporters required for GA and abscisic acid (ABA) translocation.

Multi-Knock-a multi-targeted genome-scale CRISPR toolbox to overcome functional redundancy in plants.

Plant genomes are characterized by large and complex gene families that often result in similar and partially overlapping functions. This genetic redundancy severely hampers current efforts to uncover novel phenotypes, delaying basic genetic research and breeding programmes. Here we describe the development and validation of Multi-Knock, a genome-scale clustered regularly interspaced short palindromic repeat toolbox that overcomes functional redundancy in Arabidopsis by simultaneously targeting multiple gene-family members, thus identifying genetically hidden components.

Plant Hormone Transport and Localization: Signaling Molecules on the Move.

Plant hormones are a group of small signaling molecules produced by plants at very low concentrations that have the ability to move and function at distal sites. Hormone homeostasis is critical to balance plant growth and development and is regulated at multiple levels, including hormone biosynthesis, catabolism, perception, and transduction. In addition, plants move hormones over short and long distances to regulate various developmental processes and responses to environmental factors.

ABCB-mediated shootward auxin transport feeds into the root clock.

Although strongly influenced by environmental conditions, lateral root (LR) positioning along the primary root appears to follow obediently an internal spacing mechanism dictated by auxin oscillations that prepattern the primary root, referred to as the root clock. Surprisingly, none of the hitherto characterized PIN- and ABCB-type auxin transporters seem to be involved in this LR prepatterning mechanism. Here, we characterize ABCB15, 16, 17, 18, and 22 (ABCB15-22) as novel auxin-transporting ABCBs.

Hydraulic flux-responsive hormone redistribution determines root branching.

Plant roots exhibit plasticity in their branching patterns to forage efficiently for heterogeneously distributed resources, such as soil water. The xerobranching response represses lateral root formation when roots lose contact with water. Here, we show that xerobranching is regulated by radial movement of the phloem-derived hormone abscisic acid, which disrupts intercellular communication between inner and outer cell layers through plasmodesmata.

ABA homeostasis and long-distance translocation are redundantly regulated by ABCG ABA importers.

The effects of abscisic acid (ABA) on plant growth, development, and response to the environment depend on local ABA concentrations. Here, we show that in , ABA homeostasis is regulated by two previously unknown ABA transporters. Adenosine triphosphate–binding cassette subfamily G member 17 (ABCG17) and ABCG18 are localized to the plasma membranes of leaf mesophyll and cortex cells to redundantly promote ABA import, leading to conjugated inactive ABA sinks, thus restricting stomatal closure.

Transport mechanisms of plant hormones.

Plant growth, development, and response to the environment are mediated by a group of small signaling molecules named hormones. Plants regulate hormone response pathways at multiple levels, including biosynthesis, metabolism, perception, and signaling. In addition, plants exhibit the unique ability to spatially control hormone distribution.

Cell kinetics of auxin transport and activity in Arabidopsis root growth and skewing.

Auxin is a key regulator of plant growth and development. Local auxin biosynthesis and intercellular transport generates regional gradients in the root that are instructive for processes such as specification of developmental zones that maintain root growth and tropic responses. Here we present a toolbox to study auxin-mediated root development that features: (i) the ability to control auxin synthesis with high spatio-temporal resolution and (ii) single-cell nucleus tracking and morphokinetic analysis infrastructure.

The GORKY glycoalkaloid transporter is indispensable for preventing tomato bitterness.

Fruit taste is determined by sugars, acids and in some species, bitter chemicals. Attraction of seed-dispersing organisms in nature and breeding for consumer preferences requires reduced fruit bitterness. A key metabolic shift during ripening prevents tomato fruit bitterness by eliminating α-tomatine, a renowned defence-associated Solanum alkaloid.

Cell-type action specificity of auxin on Arabidopsis root growth.

The plant hormone auxin plays a critical role in root growth and development; however, the contributions or specific roles of cell-type auxin signals in root growth and development are not well understood. Here, we mapped tissue and cell types that are important for auxin-mediated root growth and development by manipulating the local response and synthesis of auxin. Repressing auxin signaling in the epidermis, cortex, endodermis, pericycle or stele strongly inhibited root growth, with the largest effect observed in the endodermis.

Characterizing gibberellin flow using photocaged gibberellins.

Gibberellins (GAs) are ubiquitous plant hormones that coordinate central developmental and adaptive growth processes in plants. Accurate movement of GAs throughout the plant from their sources to their destination sites is emerging to be a highly regulated and directed process. We report on the development of novel photocaged gibberellins that, in combination with a genetically encoded GA-response marker, provide a unique platform to study GA movement at high-resolution, in real time and in living, intact plants.

A seed resource for screening functionally redundant genes and isolation of new mutants impaired in CO2 and ABA responses.

The identification of homologous genes with functional overlap in forward genetic screens is severely limited. Here, we report the generation of over 14000 artificial microRNA (amiRNA)-expressing plants that enable screens of the functionally redundant gene space in Arabidopsis. A protocol was developed for isolating robust and reproducible amiRNA mutants.

A transportome-scale amiRNA-based screen identifies redundant roles of Arabidopsis ABCB6 and ABCB20 in auxin transport.

Transport of signaling molecules is of major importance for regulating plant growth, development, and responses to the environment. A prime example is the spatial-distribution of auxin, which is regulated via transporters to govern developmental patterning. A critical limitation in our ability to identify transporters by forward genetic screens is their potential functional redundancy.

The KNOXI Transcription Factor SHOOT MERISTEMLESS Regulates Floral Fate in Arabidopsis.

Plants have evolved a unique and conserved developmental program that enables the conversion of leaves into floral organs. Elegant genetic and molecular work has identified key regulators of flower meristem identity. However, further understanding of flower meristem specification has been hampered by redundancy and by pleiotropic effects.

CRISPys: Optimal sgRNA Design for Editing Multiple Members of a Gene Family Using the CRISPR System.

The development of the CRISPR-Cas9 system in recent years has made eukaryotic genome editing, and specifically gene knockout for reverse genetics, a simple and effective task. The system is directed to a genomic target site by a programmed single-guide RNA (sgRNA) that base-pairs with it, subsequently leading to site-specific modifications. However, many gene families in eukaryotic genomes exhibit partially overlapping functions, and thus, the knockout of one gene might be concealed by the function of the other.

Gibberellin Localization and Transport in Plants.

Distribution patterns and finely-tuned concentration gradients of plant hormones govern plant growth and development. Gibberellin (GA) is a plant hormone regulating key processes in plants; many of them are of significant agricultural importance, such as seed germination, root and shoot elongation, flowering, and fruit patterning. Although studies have demonstrated that GA movement is essential for multiple developmental aspects, how GAs are transported throughout the plant and where exactly they accumulate remain largely unknown.

PHB3 Maintains Root Stem Cell Niche Identity through ROS-Responsive AP2/ERF Transcription Factors in Arabidopsis.

The root stem cell niche, which is composed of four mitotically inactive quiescent center (QC) cells and the surrounding actively divided stem cells in Arabidopsis, is critical for growth and root development. Here, we demonstrate that the Arabidopsis prohibitin protein PHB3 is required for the maintenance of root stem cell niche identity by both inhibiting proliferative processes in the QC and stimulating cell division in the proximal meristem (PM). PHB3 coordinates cell division and differentiation in the root apical meristem by restricting the spatial expression of ethylene response factor (ERF) transcription factors 115, 114, and 109.

Studying microstructure and microstructural changes in plant tissues by advanced diffusion magnetic resonance imaging techniques.

As sessile organisms, plants must respond to the environment by adjusting their growth and development. Most of the plant body is formed post-embryonically by continuous activity of apical and lateral meristems. The development of lateral adventitious roots is a complex process, and therefore the development of methods that can visualize, non-invasively, the plant microstructure and organ initiation that occur during growth and development is of paramount importance.

Plant Stress Tolerance Requires Auxin-Sensitive Aux/IAA Transcriptional Repressors.

The Aux/IAA proteins are auxin-sensitive repressors that mediate diverse physiological and developmental processes in plants [1, 2]. There are 29 Aux/IAA genes in Arabidopsis that exhibit unique but partially overlapping patterns of expression [3]. Although some studies have suggested that individual Aux/IAA genes have specialized function, genetic analyses of the family have been limited by the scarcity of loss-of-function phenotypes [4].

Highlighting Gibberellins Accumulation Sites in Arabidopsis thaliana Root Using Fluorescently Labeled Gibberellins.

The physical location of plant hormones is an important factor in maintaining their proper metabolism, perception, and mediated developmental responses. Thus, unveiling plant hormones dynamics at the molecule's level is essential for a comprehensive, detailed understanding of both their functions and the regulative mechanisms they are subjected to. Here, we describe the use of fluorescently labeled, bioactive gibberellins (GAs) to highlight the dynamic distribution and accumulation sites of bioactive GAs in Arabidopsis thaliana roots by confocal microscopy.

Stronger sink demand for metabolites supports dominance of the apical bud in etiolated growth.

The potato tuber is a swollen underground stem that can sprout under dark conditions. Sprouting initiates in the tuber apical bud (AP), while lateral buds (LTs) are repressed by apical dominance (AD). Under conditions of lost AD, removal of tuber LTs showed that they partially inhibit AP growth only at the AD stage.

The Arabidopsis NPF3 protein is a GA transporter.

Gibberellins (GAs) are plant hormones that promote a wide range of developmental processes. While GA signalling is well understood, little is known about how GA is transported or how GA distribution is regulated. Here we utilize fluorescently labelled GAs (GA-Fl) to screen for Arabidopsis mutants deficient in GA transport.