Publications by authors named "Eilon Shani"

30 Publications

  • Page 1 of 1

Transport mechanisms of plant hormones.

Curr Opin Plant Biol 2021 Jun 5;63:102055. Epub 2021 Jun 5.

School of Plant Sciences and Food Security, Tel Aviv University, Tel Aviv, 69978, Israel. Electronic address:

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. In recent years, multiple transporters have been identified for most of the plant hormones. Here we present an updated snapshot of the known transporters for the hormones abscisic acid, auxin, brassinosteroid, cytokinin, ethylene, gibberellin, jasmonic acid, salicylic acid, and strigolactone. We also describe new findings regarding hormone movement and elaborate on hormone substrate specificity and possible genetic redundancy in hormone transport and distribution. Finally, we discuss subcellular, cell-to-cell, and long-distance hormone movement and local hormone sinks that trigger or prevent hormone-mediated responses.
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http://dx.doi.org/10.1016/j.pbi.2021.102055DOI Listing
June 2021

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

Nat Commun 2021 03 12;12(1):1657. Epub 2021 Mar 12.

School of Plant Sciences and Food Security, Tel Aviv University, Tel Aviv, Israel.

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. Integration of these two features enables cutting-edge analysis of root development at single-cell resolution based on morphokinetic parameters under normal growth conditions and during cell-type-specific induction of auxin biosynthesis. We show directional auxin flow in the root and refine the contributions of key players in this process. In addition, we determine the quantitative kinetics of Arabidopsis root meristem skewing, which depends on local auxin gradients but does not require PIN2 and AUX1 auxin transporter activities. Beyond the mechanistic insights into root development, the tools developed here will enable biologists to study kinetics and morphology of various critical processes at the single cell-level in whole organisms.
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http://dx.doi.org/10.1038/s41467-021-21802-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7954861PMC
March 2021

The GORKY glycoalkaloid transporter is indispensable for preventing tomato bitterness.

Nat Plants 2021 04 11;7(4):468-480. Epub 2021 Mar 11.

Department of Plant and Environmental Sciences, Weizmann Institute of Science, Rehovot, Israel.

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. Here, we combined fine mapping with information from 150 resequenced genomes and genotyping a 650-tomato core collection to identify nine bitter-tasting accessions including the 'high tomatine' Peruvian landraces reported in the literature. These 'bitter' accessions contain a deletion in GORKY, a nitrate/peptide family transporter mediating α-tomatine subcellular localization during fruit ripening. GORKY exports α-tomatine and its derivatives from the vacuole to the cytosol and this facilitates the conversion of the entire α-tomatine pool to non-bitter forms, rendering the fruit palatable. Hence, GORKY activity was a notable innovation in the process of tomato fruit domestication and breeding.
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http://dx.doi.org/10.1038/s41477-021-00865-6DOI Listing
April 2021

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

Plant J 2021 May 3;106(4):928-941. Epub 2021 Apr 3.

The Key Laboratory of Plant Development and Environmental Adaptation Biology, Ministry of Education, School of Life Sciences, Shandong University, Qingdao, Shandong, China.

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. Enhancing auxin signaling in the epidermis, cortex, endodermis, pericycle or stele also caused reduced root growth, albeit to a lesser extent. Moreover, we established that root growth was inhibited by enhancement of auxin synthesis in specific cell types of the epidermis, cortex and endodermis, whereas increased auxin synthesis in the pericycle and stele had only minor effects on root growth. Our study thus establishes an association between cellular identity and cell type-specific auxin signaling that guides root growth and development.
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http://dx.doi.org/10.1111/tpj.15208DOI Listing
May 2021

Characterizing gibberellin flow using photocaged gibberellins.

Chem Sci 2019 Feb 20;10(5):1500-1505. Epub 2018 Nov 20.

School of Plant Sciences and Food Security , Faculty of Life Sciences , Tel Aviv University , Tel Aviv 69978 , Israel . Email:

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. By applying this platform to the endogenous bioactive gibberellin GA, we measure kinetic parameters of its flow, such as decay length and velocity, .
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http://dx.doi.org/10.1039/c8sc04528cDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6354844PMC
February 2019

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

J Exp Bot 2019 01;70(2):641-651

Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, USA.

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. Examples of validation approaches and essential controls are presented for two new amiRNA mutants that exhibit genetically redundant phenotypes and circumvent double mutant lethality. In a forward genetic screen for abscisic acid (ABA)-mediated inhibition of seed germination, amiRNAs that target combinations of known redundant ABA receptor and SnRK2 kinase genes were rapidly isolated, providing a strong proof of principle for this approach. A new ABA-insensitive amiRNA line that targets three avirulence-induced gene 2(-like) genes was isolated . A thermal imaging screen for plants with impaired stomatal opening in response to low CO2 exposure led to the isolation of a new amiRNA targeting two essential proteasomal subunits, PAB1 and PAB2. The seed library of 11000 T2 amiRNA lines (with 3000 lines in progress) generated here provides a new platform for forward genetic screens and has been made available to the Arabidopsis Biological Resource Center (ABRC). Optimized procedures for amiRNA screening and controls are described.
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http://dx.doi.org/10.1093/jxb/ery363DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6322574PMC
January 2019

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

Nat Commun 2018 10 11;9(1):4204. Epub 2018 Oct 11.

School of Plant Sciences and Food Security, Tel Aviv University, Tel Aviv, 69978, Israel.

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. Here, we overcome part of this functional redundancy via a transportome, multi-targeted forward-genetic screen using artificial-microRNAs (amiRNAs). We generate a library of 3000 plant lines expressing 1777 amiRNAs, designed to target closely homologous genes within subclades of transporter families and identify, genotype and quantitatively phenotype, 80 lines showing reproducible shoot growth phenotypes. Within this population, we discover and characterize a strong redundant role for the unstudied ABCB6 and ABCB20 genes in auxin transport and response. The unique multi-targeted lines generated in this study could serve as a genetic resource that is expected to reveal additional transporters.
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http://dx.doi.org/10.1038/s41467-018-06410-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6182007PMC
October 2018

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

Plant Cell 2018 06 9;30(6):1309-1321. Epub 2018 May 9.

School of Plant Sciences and Food Security, Tel Aviv University, Tel Aviv 69978, Israel

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. The KNOXI transcription factor SHOOT MERISTEMLESS (STM) is a well-characterized regulator of shoot apical meristem maintenance. loss-of-function mutants arrest shortly after germination; therefore, the knowledge on later roles of STM in later processes, including flower development, is limited. Here, we uncover a role for STM in the specification of flower meristem identity. Silencing in the () expression domain in the mutant background resulted in a leafy-flower phenotype, and an intermediate allele enhanced the flower meristem identity phenotype of Transcriptional profiling of perturbation suggested that STM activity affects multiple floral fate genes, among them the F-box protein-encoding gene (). In agreement with this notion, enhanced the floral fate phenotype, and ectopic expression rescued the leafy flowers in genetic backgrounds with compromised and activities. This work suggests a genetic mechanism that underlies the activity of in the specification of flower meristem identity.
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http://dx.doi.org/10.1105/tpc.18.00222DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6048794PMC
June 2018

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

J Mol Biol 2018 07 3;430(15):2184-2195. Epub 2018 Apr 3.

School of Plant Sciences and Food security, Tel Aviv University, Ramat Aviv, 69978, Israel. Electronic address:

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. In such cases, the reduced specificity of the CRISPR-Cas9 system, which may lead to the modification of genomic sites that are not identical to the sgRNA, can be harnessed for the simultaneous knockout of multiple homologous genes. We introduce CRISPys, an algorithm for the optimal design of sgRNAs that would potentially target multiple members of a given gene family. CRISPys first clusters all the potential targets in the input sequences into a hierarchical tree structure that specifies the similarity among them. Then, sgRNAs are proposed in the internal nodes of the tree by embedding mismatches where needed, such that the efficiency to edit the induced targets is maximized. We suggest several approaches for designing the optimal individual sgRNA and an approach to compute the optimal set of sgRNAs for cases when the experimental platform allows for more than one. The latter may optionally account for the homologous relationships among gene-family members. We further show that CRISPys outperforms simpler alignment-based techniques by in silico examination over all gene families in the Solanum lycopersicum genome.
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http://dx.doi.org/10.1016/j.jmb.2018.03.019DOI Listing
July 2018

Gibberellin Localization and Transport in Plants.

Trends Plant Sci 2018 05 9;23(5):410-421. Epub 2018 Mar 9.

School of Plant Sciences and Food Security, Tel Aviv University, Tel Aviv, Israel. Electronic address:

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. Here, we summarize recent findings from studies of GA movement and localization, and discuss the importance of GA intermediates in long- and short-distance movement. We further review recently identified Arabidopsis GA transporters and highlight their complex specialization and robust functional redundancy in GA transport activity.
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http://dx.doi.org/10.1016/j.tplants.2018.02.005DOI Listing
May 2018

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

Cell Rep 2018 01;22(5):1350-1363

The Key Laboratory of Plant Cell Engineering and Germplasm Innovation, Ministry of Education, College of Life Sciences, Shandong University, Jinan, 250100 Shandong, China. Electronic address:

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. ERF115, ERF114, and ERF109 mediate ROS signaling, in a PLT-independent manner, to control root stem cell niche maintenance and root growth through phytosulfokine (PSK) peptide hormones in Arabidopsis.
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http://dx.doi.org/10.1016/j.celrep.2017.12.105DOI Listing
January 2018

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

J Exp Bot 2017 04;68(9):2245-2257

School of Chemistry, The Sackler Faculty of Exact Sciences, and.

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. In this study, relaxation-based and advanced diffusion magnetic resonance imaging (MRI) methods including diffusion tensor (DTI), q-space diffusion imaging (QSI), and double-pulsed-field-gradient (d-PFG) MRI, at 14.1 T, were used to characterize the hypocotyl microstructure and the microstructural changes that occurred during the development of lateral adventitious roots in tomato. Better contrast was observed in relaxation-based MRI using higher in-plane resolution but this also resulted in a significant reduction in the signal-to-noise ratio of the T2-weighted MR images. Diffusion MRI revealed that water diffusion is highly anisotropic in the vascular cylinder. QSI and d-PGSE MRI showed that in the vascular cylinder some of the cells have sizes in the range of 6-10 μm. The MR images captured cell reorganization during adventitious root formation in the periphery of the primary vascular bundles, adjacent to the xylem pole that broke through the cortex and epidermis layers. This study demonstrates that MRI and diffusion MRI methods allow the non-invasive study of microstructural features of plants, and enable microstructural changes associated with adventitious root formation to be followed.
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http://dx.doi.org/10.1093/jxb/erx106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5447889PMC
April 2017

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

Curr Biol 2017 Feb 19;27(3):437-444. Epub 2017 Jan 19.

Section of Cell and Developmental Biology and Howard Hughes Medical Institute, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA. Electronic address:

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]. Furthermore, with a few exceptions, our knowledge of the factors that regulate Aux/IAA expression is limited [1, 5]. We hypothesize that transcriptional control of Aux/IAA genes plays a central role in the establishment of the auxin-signaling pathways that regulate organogenesis, growth, and environmental response. Here, we describe a screen for transcription factors (TFs) that regulate the Aux/IAA genes. We identify TFs from 38 families, including 26 members of the DREB/CBF family. Several DREB/CBF TFs directly promote transcription of the IAA5 and IAA19 genes in response to abiotic stress. Recessive mutations in these IAA genes result in decreased tolerance to stress conditions, demonstrating a role for auxin in abiotic stress. Our results demonstrate that stress pathways interact with the auxin gene regulatory network (GRN) through transcription of the Aux/IAA genes. We propose that the Aux/IAA genes function as hubs that integrate genetic and environmental information to achieve the appropriate developmental or physiological outcome.
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http://dx.doi.org/10.1016/j.cub.2016.12.016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5296222PMC
February 2017

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

Methods Mol Biol 2017 ;1497:91-97

Department of Molecular Biology and Ecology of Plants, Life Sciences Faculty, Tel-Aviv University, PO Box 39040, 6997801, Tel-Aviv, Israel.

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.
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http://dx.doi.org/10.1007/978-1-4939-6469-7_10DOI Listing
January 2018

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

J Exp Bot 2016 10 31;67(18):5495-5508. Epub 2016 Aug 31.

Department of Postharvest Science of Fresh Produce, The Volcani Center, ARO, Rishon LeZion, Israel

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. Detached buds were inhibited by exogenous application of naphthaleneacetic acid (NAA), whereas 6-benzyladenine (6-BA) and gibberellic acid (GA) induced bud burst and elongation, respectively. NAA, applied after 6-BA or GA, nullified the latters' growth-stimulating effect in both the AP and LTs. GA applied to the fifth-position LT was transported mainly to the tuber's AP. GA treatment also resulted in increased indole-3-acetic acid (IAA) concentration and cis-zeatin O-glucoside in the AP. In a tuber tissue strip that included two or three buds connected by the peripheral vascular system, treatment of a LT with GA affected only the AP side of the strip, suggesting that the AP is the strongest sink for GA, which induces its etiolated elongation. Dipping etiolated sprouts in labeled GA showed specific accumulation of the signal in the AP. Transcriptome analysis of GA's effect showed that genes related to the cell cycle, cell proliferation, and hormone transport are up-regulated in the AP as compared to the LT. Sink demand for metabolites is suggested to support AD in etiolated stem growth by inducing differential gene expression in the AP.
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http://dx.doi.org/10.1093/jxb/erw315DOI Listing
October 2016

The Arabidopsis NPF3 protein is a GA transporter.

Nat Commun 2016 May 3;7:11486. Epub 2016 May 3.

Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv 69978, Israel.

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. We show that the NPF3 transporter efficiently transports GA across cell membranes in vitro and GA-Fl in vivo. NPF3 is expressed in root endodermis and repressed by GA. NPF3 is targeted to the plasma membrane and subject to rapid BFA-dependent recycling. We show that abscisic acid (ABA), an antagonist of GA, is also transported by NPF3 in vitro. ABA promotes NPF3 expression and GA-Fl uptake in plants. On the basis of these results, we propose that GA distribution and activity in Arabidopsis is partly regulated by NPF3 acting as an influx carrier and that GA-ABA interaction may occur at the level of transport.
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http://dx.doi.org/10.1038/ncomms11486DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4857387PMC
May 2016

Auxin response under osmotic stress.

Plant Mol Biol 2016 Aug 6;91(6):661-72. Epub 2016 Apr 6.

Department of Molecular Biology and Ecology of Plants, Tel Aviv University, 69978, Tel Aviv, Israel.

The phytohormone auxin (indole-3-acetic acid, IAA) is a small organic molecule that coordinates many of the key processes in plant development and adaptive growth. Plants regulate the auxin response pathways at multiple levels including biosynthesis, metabolism, transport and perception. One of the most striking aspects of plant plasticity is the modulation of development in response to changing growth environments. In this review, we explore recent findings correlating auxin response-dependent growth and development with osmotic stresses. Studies of water deficit, dehydration, salt, and other osmotic stresses point towards direct and indirect molecular perturbations in the auxin pathway. Osmotic stress stimuli modulate auxin responses by affecting auxin biosynthesis (YUC, TAA1), transport (PIN), perception (TIR/AFB, Aux/IAA), and inactivation/conjugation (GH3, miR167, IAR3) to coordinate growth and patterning. In turn, stress-modulated auxin gradients drive physiological and developmental mechanisms such as stomata aperture, aquaporin and lateral root positioning. We conclude by arguing that auxin-mediated growth inhibition under abiotic stress conditions is one of the developmental and physiological strategies to acclimate to the changing environment.
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http://dx.doi.org/10.1007/s11103-016-0476-5DOI Listing
August 2016

TEMPRANILLO Reveals the Mesophyll as Crucial for Epidermal Trichome Formation.

Plant Physiol 2016 Mar 22;170(3):1624-39. Epub 2016 Jan 22.

Centre for Research in Agricultural Genomics, CSIC-IRTA-UAB-UB, Campus UAB, Bellaterra (Cerdanyola del Vallès) 08193 Barcelona, Spain (L.M.-H., A.E.A.-J., M.O., P.S.-L., S.P.); ICREA (Institució Catalana de Recerca i Estudis Avançats), Barcelona, Spain (S.P.); and Department of Molecular Biology and Ecology of Plants, Faculty of Life Sciences, Tel Aviv University, 39040, Tel Aviv, Israel (R.W., E.S.)

Plant trichomes are defensive specialized epidermal cells. In all accepted models, the epidermis is the layer involved in trichome formation, a process controlled by gibberellins (GAs) in Arabidopsis rosette leaves. Indeed, GA activates a genetic cascade in the epidermis for trichome initiation. Here we report that TEMPRANILLO (TEM) genes negatively control trichome initiation not only from the epidermis but also from the leaf layer underneath the epidermis, the mesophyll. Plants over-expressing or reducing TEM specifically in the mesophyll, display lower or higher trichome numbers, respectively. We surprisingly found that fluorescently labeled GA3 accumulates exclusively in the mesophyll of leaves, but not in the epidermis, and that TEM reduces its accumulation and the expression of several newly identified GA transporters. This strongly suggests that TEM plays an essential role, not only in GA biosynthesis, but also in regulating GA distribution in the mesophyll, which in turn directs epidermal trichome formation. Moreover, we show that TEM also acts as a link between GA and cytokinin signaling in the epidermis by negatively regulating downstream genes of both trichome formation pathways. Overall, these results call for a re-evaluation of the present theories of trichome formation as they reveal mesophyll essential during epidermal trichome initiation.
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http://dx.doi.org/10.1104/pp.15.01309DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4775113PMC
March 2016

The glucosinolate breakdown product indole-3-carbinol acts as an auxin antagonist in roots of Arabidopsis thaliana.

Plant J 2015 May 13;82(4):547-55. Epub 2015 Apr 13.

Molecular Biology and Ecology of Plants, Tel Aviv University, Ramat Aviv, 69978, Israel.

The glucosinolate breakdown product indole-3-carbinol functions in cruciferous vegetables as a protective agent against foraging insects. While the toxic and deterrent effects of glucosinolate breakdown on herbivores and pathogens have been studied extensively, the secondary responses that are induced in the plant by indole-3-carbinol remain relatively uninvestigated. Here we examined the hypothesis that indole-3-carbinol plays a role in influencing plant growth and development by manipulating auxin signaling. We show that indole-3-carbinol rapidly and reversibly inhibits root elongation in a dose-dependent manner, and that this inhibition is accompanied by a loss of auxin activity in the root meristem. A direct interaction between indole-3-carbinol and the auxin perception machinery was suggested, as application of indole-3-carbinol rescues auxin-induced root phenotypes. In vitro and yeast-based protein interaction studies showed that indole-3-carbinol perturbs the auxin-dependent interaction of Transport Inhibitor Response (TIR1) with auxin/3-indoleacetic acid (Aux/IAAs) proteins, further supporting the possibility that indole-3-carbinol acts as an auxin antagonist. The results indicate that chemicals whose production is induced by herbivory, such as indole-3-carbinol, function not only to repel herbivores, but also as signaling molecules that directly compete with auxin to fine tune plant growth and development.
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http://dx.doi.org/10.1111/tpj.12824DOI Listing
May 2015

A map of cell type-specific auxin responses.

Mol Syst Biol 2013 ;9:688

1] Biology Department, Center for Genomics and Systems Biology, New York University, New York, NY, USA [2] Department of Cell and Developmental Biology, UCSD, La Jolla, CA, USA.

In plants, changes in local auxin concentrations can trigger a range of developmental processes as distinct tissues respond differently to the same auxin stimulus. However, little is known about how auxin is interpreted by individual cell types. We performed a transcriptomic analysis of responses to auxin within four distinct tissues of the Arabidopsis thaliana root and demonstrate that different cell types show competence for discrete responses. The majority of auxin-responsive genes displayed a spatial bias in their induction or repression. The novel data set was used to examine how auxin influences tissue-specific transcriptional regulation of cell-identity markers. Additionally, the data were used in combination with spatial expression maps of the root to plot a transcriptomic auxin-response gradient across the apical and basal meristem. The readout revealed a strong correlation for thousands of genes between the relative response to auxin and expression along the longitudinal axis of the root. This data set and comparative analysis provide a transcriptome-level spatial breakdown of the response to auxin within an organ where this hormone mediates many aspects of development.
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http://dx.doi.org/10.1038/msb.2013.40DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3792342PMC
March 2014

BSKs are partially redundant positive regulators of brassinosteroid signaling in Arabidopsis.

Plant J 2013 Jun 15;74(6):905-19. Epub 2013 Apr 15.

Department of Molecular Biology and Ecology of Plants, Tel-Aviv University, Tel-Aviv, 69978, Israel.

Arabidopsis thaliana brassinosteroid signaling kinases (BSKs) constitute a receptor-like cytoplasmic kinase sub-family (RLCK-XII) with 12 members. Previous analysis demonstrated a positive role for BSK1 and BSK3 in the initial steps of brassinosteroid (BR) signal transduction. To investigate the function of BSKs in plant growth and BR signaling, we characterized T-DNA insertion lines for eight BSK genes (BSK1-BSK8) and multiple mutant combinations. Simultaneous elimination of three BSK genes caused alterations in growth and the BR response, and the most severe phenotypes were observed in the bsk3,4,7,8 quadruple and bsk3,4,6,7,8 pentuple mutants, which displayed reduced rosette size, leaf curling and enhanced leaf inclination. In addition, upon treatment with 24-epibrassinolide, these mutants showed reduced hypocotyl elongation, enhanced root growth and alteration in the expression of BR-responsive genes. Some mutant combinations also showed antagonistic interactions. In support of a redundant function in BR signaling, multiple BSKs interacted in vivo with the BR receptor BRI1, and served as its phosphorylation substrates in vitro. The BIN2 and BIL2 GSK3-like kinases, which are negative regulators of BR signaling, interacted in vivo with BSKs and phosphorylated them in vitro, probably at different sites to BRI1. This study demonstrates redundant biological functions for BSKs, and suggests the existence of a regulatory link between BSKs and GSK3-like kinases.
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http://dx.doi.org/10.1111/tpj.12175DOI Listing
June 2013

Gibberellins accumulate in the elongating endodermal cells of Arabidopsis root.

Proc Natl Acad Sci U S A 2013 Mar 4;110(12):4834-9. Epub 2013 Feb 4.

Section of Cell and Developmental Biology, University of California at San Diego, La Jolla, CA 92093, USA.

Plant hormones are small-molecule signaling compounds that are collectively involved in all aspects of plant growth and development. Unlike animals, plants actively regulate the spatial distribution of several of their hormones. For example, auxin transport results in the formation of auxin maxima that have a key role in developmental patterning. However, the spatial distribution of the other plant hormones, including gibberellic acid (GA), is largely unknown. To address this, we generated two bioactive fluorescent GA compounds and studied their distribution in Arabidopsis thaliana roots. The labeled GAs specifically accumulated in the endodermal cells of the root elongation zone. Pharmacological studies, along with examination of mutants affected in endodermal specification, indicate that GA accumulation is an active and highly regulated process. Our results strongly suggest the presence of an active GA transport mechanism that would represent an additional level of GA regulation.
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http://dx.doi.org/10.1073/pnas.1300436110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3606980PMC
March 2013

ENTIRE and GOBLET promote leaflet development in tomato by modulating auxin response.

Plant J 2012 Jun 31;70(6):903-15. Epub 2012 Mar 31.

The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture and The Otto Warburg Minerva Center for Agricultural Biotechnology, Hebrew University, P.O. Box 12, Rehovot 76100, Israel.

Compound leaves produce leaflets in a highly controlled yet flexible pattern. Here, we investigate the interaction between auxin, the putative auxin response inhibitor ENTIRE (E, SlIAA9) and the CUC transcription factor GOBLET (GOB) in compound-leaf development in tomato (Solanum lycopersicum). Auxin maxima, monitored by the auxin response sensor DR5, marked and preceded leaflet and lobe initiation. The DR5 signal increased, but maxima were partially retained in response to the external or internal elevation of auxin levels. E directly interacted with the auxin receptors SlTIR1 and SlAFB6. Furthermore, E was stabilized by a mutation in domain II of the protein and by the inhibition of auxin or proteasome activity, implying that E is subjected to auxin-mediated degradation. In e mutants the DR5 signal expanded to include the complete leaf margin, and leaf-specific overexpression of a stabilized form of E inhibited the DR5 signal and lamina expansion. Genetic manipulation of GOB activity altered the distribution of the DR5 signal, and the inhibition of auxin transport or activity suppressed the GOB overexpression phenotype, suggesting that auxin mediates GOB-regulated leaf patterning. Whereas leaves of single e or gob mutants developed only primary leaflets, the downregulation of both E and GOB resulted in the complete abolishment of leaflet initiation, and in a strong DR5 signal throughout the leaf margin. These results suggest that E and GOB modulate auxin response and leaflet morphogenesis via partly redundant pathways, and that proper leaflet initiation and separation requires distinct boundaries between regions of lamina growth and adjacent regions in which growth is inhibited.
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http://dx.doi.org/10.1111/j.1365-313X.2012.04939.xDOI Listing
June 2012

Gibberellin partly mediates LANCEOLATE activity in tomato.

Plant J 2011 Nov 30;68(4):571-82. Epub 2011 Aug 30.

The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture and the Otto Warburg Minerva Center for Agricultural Biotechnology, Hebrew University, Rehovot 76100, Israel.

Elaboration of a compound leaf shape depends on extended morphogenetic activity in developing leaves. In tomato (Solanum lycopersicum), the CIN-TCP transcription factor LANCEOLATE (LA) promotes leaf differentiation. LA is negatively regulated by miR319 during the early stages of leaf development, and decreased sensitivity of LA mRNA to miR319 recognition in the semi-dominant mutant La leads to prematurely increased LA expression, precocious leaf differentiation and a simpler and smaller leaf. Increased levels or responses of the plant hormone gibberellin (GA) in tomato leaves also led to a simplified leaf form. Here, we show that LA activity is mediated in part by GA. Expression of the SlGA20 oxidase1 (SlGA20ox1) gene, which encodes an enzyme in the GA biosynthesis pathway, is increased in gain-of-function La mutants and reduced in plants that over-express miR319. Conversely, the transcript levels of the GA deactivation gene SlGA2 oxidase4 (SlGA2ox4) are increased in plants over-expressing miR319. The miR319 over-expression phenotype is suppressed by exogenous GA application and by a mutation in the PROCERA (PRO) gene, which encodes an inhibitor of the GA response. SlGA2ox4 is expressed in initiating leaflets during early leaf development. Its expression expands as a result of miR319 over-expression, and its over-expression leads to increased leaf complexity. These results suggest that LA activity is partly mediated by positive regulation of the GA response, probably by regulation of GA levels.
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http://dx.doi.org/10.1111/j.1365-313X.2011.04716.xDOI Listing
November 2011

From organelle to organ: ZRIZI MATE-Type transporter is an organelle transporter that enhances organ initiation.

Plant Cell Physiol 2011 Mar 20;52(3):518-27. Epub 2011 Jan 20.

The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture and The Otto Warburg Minerva Center for Agricultural Biotechnology, Hebrew University, Rehovot 76100, Israel.

Plant architecture is a predictable but flexible trait. The timing and position of organ initiation from the shoot apical meristem (SAM) contribute to the final plant form. While much progress has been made recently in understanding how the site of leaf initiation is determined, the mechanism underlying the temporal interval between leaf primordia is still largely unknown. The Arabidopsis ZRIZI (ZRZ) gene belongs to a large gene family encoding multidrug and toxic compound extrusion (MATE) transporters. Unique among plant MATE transporters identified so far, ZRZ is localized to the membrane of a small organelle, possibly the mitochondria. Plants overexpressing ZRZ in initiating leaves are short, produce leaves much faster than wild-type plants and show enhanced growth of axillary buds. These results suggest that ZRZ is involved in communicating a leaf-borne signal that determines the rate of organ initiation.
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http://dx.doi.org/10.1093/pcp/pcr007DOI Listing
March 2011

Negative reciprocal interactions between gibberellin and cytokinin in tomato.

New Phytol 2011 May 18;190(3):609-17. Epub 2011 Jan 18.

Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.

• The hormones gibberellin (GA) and cytokinin (CK) exhibit antagonistic effects on various processes in many species. Previous studies in Arabidopsis have shown that GA inhibits CK signaling. Here, we have investigated the cross-talk between GA and CK in tomato (Solanum lycopersicum). • We altered the balance between GA and CK activities by exogenous applications and genetic manipulations, and tested an array of physiological and developmental responses. • GA and CK showed antagonistic effects on various developmental and molecular processes during tomato plant growth. GA inhibited all tested CK responses, including the induction of the CK primary response genes, type A Tomato Response Regulators (TRRs). CK also inhibited a subset of GA responses. In contrast with exogenous application of GA, the endogenous GA-independent GA signal generated by the loss of the DELLA gene PROCERA (PRO) did not repress CK-regulated processes, such as anthocyanin accumulation, TRR expression and leaf complexity. • Our results suggest a mutual antagonistic interaction between GA and CK in tomato. Although GA may inhibit early steps in the CK response pathway via a DELLA-independent pathway, CK appears to affect downstream branch(es) of the GA signaling pathway. The ratio between the two hormones, rather than their absolute levels, determines the final response.
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http://dx.doi.org/10.1111/j.1469-8137.2010.03616.xDOI Listing
May 2011

Cytokinin regulates compound leaf development in tomato.

Plant Cell 2010 Oct 19;22(10):3206-17. Epub 2010 Oct 19.

The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Hebrew University, Rehovot, Israel.

Leaf shape diversity relies on transient morphogenetic activity in leaf margins. However, how this morphogenetic capacity is maintained is still poorly understood. Here, we uncover a role for the hormone cytokinin (CK) in the regulation of morphogenetic activity of compound leaves in tomato (Solanum lycopersicum). Manipulation of CK levels led to alterations in leaf complexity and revealed a unique potential for prolonged growth and morphogenesis in tomato leaves. We further demonstrate that the effect of CK on leaf complexity depends on proper localization of auxin signaling. Genetic analysis showed that reduction of CK levels suppresses the effect of Knotted1 like homeobox (KNOXI) proteins on leaf shape and that CK can substitute for KNOXI activity at the leaf margin, suggesting that CK mediates the activity of KNOXI proteins in the regulation of leaf shape. These results imply that CK regulates flexible leaf patterning by dynamic interaction with additional hormones and transcription factors.
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http://dx.doi.org/10.1105/tpc.110.078253DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2990126PMC
October 2010

Stage-specific regulation of Solanum lycopersicum leaf maturation by class 1 KNOTTED1-LIKE HOMEOBOX proteins.

Plant Cell 2009 Oct 9;21(10):3078-92. Epub 2009 Oct 9.

Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Otto Warburg Minerva Center for Agricultural Biotechnology, Hebrew University, Rehovot 76100, Israel.

Class 1 KNOTTED1-LIKE HOMEOBOX (KNOXI) genes encode transcription factors that are expressed in the shoot apical meristem (SAM) and are essential for SAM maintenance. In some species with compound leaves, including tomato (Solanum lycopersicum), KNOXI genes are also expressed during leaf development and affect leaf morphology. To dissect the role of KNOXI proteins in leaf patterning, we expressed in tomato leaves a fusion of the tomato KNOXI gene Tkn2 with a sequence encoding a repressor domain, expected to repress common targets of tomato KNOXI proteins. This resulted in the formation of small, narrow, and simple leaves due to accelerated differentiation. Overexpression of the wild-type form of Tkn1 or Tkn2 in young leaves also resulted in narrow and simple leaves, but in this case, leaf development was blocked at the initiation stage. Expression of Tkn1 or Tkn2 during a series of spatial and temporal windows in leaf development identified leaf initiation and primary morphogenesis as specific developmental contexts at which the tomato leaf is responsive to KNOXI activity. Arabidopsis thaliana leaves responded to overexpression of Arabidopsis or tomato KNOXI genes during the morphogenetic stage but were largely insensitive to their overexpression during leaf initiation. These results imply that KNOXI proteins act at specific stages within the compound-leaf development program to delay maturation and enable leaflet formation, rather than set the compound leaf route.
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http://dx.doi.org/10.1105/tpc.109.068148DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2782295PMC
October 2009

The role of hormones in shoot apical meristem function.

Curr Opin Plant Biol 2006 Oct 28;9(5):484-9. Epub 2006 Jul 28.

The Robert H Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agriculture, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot, Israel.

Plant organs are produced in meristems in a continuous and predictable but nevertheless flexible manner. Phytohormones and transcription factors cooperate to balance meristem maintenance and organ production. Recent research has provided clues to the mechanisms underlying this cooperation. KNOTTED1-like homeobox (KNOX) and WUSCHEL (WUS) transcription factors facilitate high cytokinin activity in the shoot apical meristem (SAM), whereas high gibberellin and auxin activities promote the initiation of lateral organs at specific sites in the SAM flanks.
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http://dx.doi.org/10.1016/j.pbi.2006.07.008DOI Listing
October 2006

Arabidopsis KNOXI proteins activate cytokinin biosynthesis.

Curr Biol 2005 Sep;15(17):1566-71

The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, Food, and Environmental Quality Sciences, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel.

Plant architecture is shaped through the continuous formation of organs by meristems. Class I KNOTTED1-like homeobox (KNOXI) genes are expressed in the shoot apical meristem (SAM) and are required for SAM maintenance. KNOXI proteins and cytokinin, a plant hormone intimately associated with the regulation of cell division, share overlapping roles, such as meristem maintenance and repression of senescence, but their mechanistic and hierarchical relationship have yet to be defined. Here, we show that activation of three different KNOXI proteins using an inducible system resulted in a rapid increase in mRNA levels of the cytokinin biosynthesis gene isopentenyl transferase 7 (AtIPT7) and in the activation of ARR5, a cytokinin response factor. We further demonstrate a rapid and dramatic increase in cytokinin levels following activation of the KNOXI protein SHOOT MERISTEMLESS (STM). Application of exogenous cytokinin or expression of a cytokinin biosynthesis gene through the STM promoter partially rescued the stm mutant. We conclude that activation of cytokinin biosynthesis mediates KNOXI function in meristem maintenance. KNOXI proteins emerge as central regulators of hormone levels in plant meristems.
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http://dx.doi.org/10.1016/j.cub.2005.07.060DOI Listing
September 2005