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Carol A. Peterson - One of the best experts on this subject based on the ideXlab platform.
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soybean root suberin anatomical distribution chemical composition and relationship to partial resistance to phytophthora sojae
Plant Physiology, 2007Co-Authors: Raymond Thomas, Carol A. Peterson, Xingxiao Fang, Kosala Ranathunge, Terry R Anderson, Mark A BernardsAbstract:Soybean (Glycine max L. Merr.) is a versatile and important agronomic crop grown worldwide. Each year millions of dollars of potential yield revenues are lost due to a root rot disease caused by the oomycete Phytophthora sojae (Kaufmann & Gerdemann). Since the root is the primary site of infection by this organism, we undertook an examination of the physicochemical barriers in soybean root, namely, the suberized walls of the epidermis and Endodermis, to establish whether or not preformed suberin (i.e. naturally present in noninfected plants) could have a role in partial resistance to P. sojae. Herein we describe the anatomical distribution and chemical composition of soybean root suberin as well as its relationship to partial resistance to P. sojae. Soybean roots contain a state I Endodermis (Casparian bands only) within the first 80 mm of the root tip, and a state II Endodermis (Casparian bands and some cells with suberin lamellae) in more proximal regions. A state III Endodermis (with thick, cellulosic, tertiary walls) was not present within the 200-mm-long roots examined. An exodermis was also absent, but some walls of the epidermal and neighboring cortical cells were suberized. Chemically, soybean root suberin resembles a typical suberin, and consists of waxes, fatty acids, ω-hydroxy acids, α,ω-diacids, primary alcohols, and guaiacyl- and syringyl-substituted phenolics. Total suberin analysis of isolated soybean epidermis/outer cortex and Endodermis tissues demonstrated (1) significantly higher amounts in the Endodermis compared to the epidermis/outer cortex, (2) increased amounts in the Endodermis as the root matured from state I to state II, (3) increased amounts in the epidermis/outer cortex along the axis of the root, and (4) significantly higher amounts in tissues isolated from a cultivar (‘Conrad’) with a high degree of partial resistance to P. sojae compared with a susceptible line (OX760-6). This latter correlation was extended by an analysis of nine independent and 32 recombinant inbred lines (derived from a ‘Conrad’ × OX760-6 cross) ranging in partial resistance to P. sojae: Strong negative correlations (−0.89 and −0.72, respectively) were observed between the amount of the aliphatic component of root suberin and plant mortality in P. sojae-infested fields.
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current insights into the development structure and chemistry of the Endodermis and exodermis of roots
Botany, 2003Co-Authors: Carol A. PetersonAbstract:The Endodermis and exodermis are the inner- and outermost cortical layers, respectively, of a root. Both are characterized by the development of Casparian bands in their anticlinal walls. Endodermal Casparian bands normally appear within 10 mm of the root tip, while exodermal Casparian bands are typically deposited farther from the tip. All Casparian bands contain the biopolymers lignin and suberin, allowing the Endodermis and exodermis to serve as filtration sites for the passive movement of ions between the soil solution and the stele. Later in development, suberin lamellae are frequently deposited as secondary walls, which will reduce the transmembrane transport of ions and water. In some species, tertiary walls are also formed; their main function is postulated to be mechanical support of the root. Recent research with fluorescence and electron microscopy has revealed some important details of development and structure of these wall modifications. Further, chemical analyses of enzymatically isolated w...
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root Endodermis and exodermis structure function and responses to the environment
Journal of Plant Growth Regulation, 2002Co-Authors: Daryl E Enstone, Carol A. PetersonAbstract:Roots of virtually all vascular plants have an Endodermis with a Casparian band, and the majority of angiosperm roots tested also have an exodermis with a Casparian band. Both the Endodermis and exodermis may develop suberin lamellae and thick, tertiary walls. Each of these wall modifications has its own function(s). The endodermal Casparian band prevents the unimpeded movement of apoplastic substances into the stele and also prevents the backflow of ions that have moved into the stele symplastically and then were released into its apoplast. In roots with a mature exodermis, the barrier to apoplastic inflow of ions occurs near the root surface, but prevention of backflow of ions from the stele remains a function of the Endodermis. The suberin lamellae protect against pathogen invasion and possibly root drying during times of stress. Tertiary walls of the Endodermis and exodermis are believed to function in mechanical support of the root, but this idea remains to be tested. During stress, root growth rates decline, and the Endodermis and exodermis develop closer to the root tip. In two cases, stress is known to induce the formation of an exodermis, and in several other cases to accelerate the development of both the exodermis and Endodermis. The responses of the Endodermis and exodermis to drought, exposure to moist air, flooding, salinity, ion deficiency, acidity, and mechanical impedance are discussed.
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development of cell wall modifications in the Endodermis and exodermis of allium cepa roots
Botany, 2001Co-Authors: Carol A. PetersonAbstract:The cytological events of wall modification in the Endodermis and exodermis of Allium cepa L. roots were examined with fluorescence and transmission electron microscopy. In the Endodermis, Casparian bands, suberin lamellae, and tertiary walls developed in succession. At the site of the future Casparian band, the plasma membrane was bound to the wall before deposition of detectable hydrophobic components in the radial wall. Suberin lamellae were deposited on the inner faces of the primary walls, first along the outer tangential walls and then the inner tangential walls. On both walls, segments of the lamellae were formed earlier in primary pit fields than at nonprimary pit field regions. Suberin lamellae then extended to the radial walls. When they reached the Casparian bands, the lamellae intruded between the bound plasma membranes and the walls, so that the cells' plasma membranes remained intact. In this way, suberin lamellae that were continuous around the cells were laid down. Later, tertiary walls we...
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development of the Endodermis and hypodermis of typha glauca godr and typha angustifolia l roots
Botany, 1999Co-Authors: James L. Seago, Carol A. Peterson, Daryl E Enstone, Chris A ScholeyAbstract:The development of the Endodermis and hypodermis in adventitious roots of Typha angustifolia L. and Typha glauca Godr. was followed from the apical meristem to full maturity. The Endodermis was typical, developing a thin Casparian band near the root tip, followed by suberin lamellae and asymmetric, secondary, lignified walls (C-type at maturity). Passage cells were present at an intermediate stage but eventually disappeared when all cells developed lamellae and secondary walls. The hypodermis was multiple (four to six layers at maturity) and began differentiating near the root tip. Here, the radial and transverse walls of the outermost layer did not dissolve in strong acid and the former were wavy in the longitudinal direction, both features characteristic of a Casparian band, but these walls were permeable to berberine. No other indication of a wall modification was seen for 3 weeks, at which time the root had become determinate and aerenchyma was beginning to form in the midcortex. Casparian bands, whic...
Niko Geldner - One of the best experts on this subject based on the ideXlab platform.
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root endodermal barrier system contributes to defence against plant parasitic cyst and root knot nematodes
Plant Journal, 2019Co-Authors: Julia Holbein, Rochus Franke, Lukas Schreiber, Peter Marhavý, Satoshi Fujita, M Gorecka, Miroslaw Sobczak, Niko Geldner, Florian M W Grundler, Shahid SiddiqueAbstract:Plant-parasitic nematodes (PPNs) cause tremendous yield losses worldwide in almost all economically important crops. The agriculturally most important PPNs belong to a small group of root-infecting sedentary endoparasites that includes cyst and root-knot nematodes. Both cyst and root-knot nematodes induce specialized long-term feeding structures in root vasculature from which they obtain their nutrients. A specialized cell layer in roots called the Endodermis, which has cell walls reinforced with suberin deposits and a lignin-based Casparian strip (CS), protects the vascular cylinder against abiotic and biotic threats. To date, the role of the Endodermis, and especially of suberin and the CS, during plant-nematode interactions was largely unknown. Here, we analyzed the role of suberin and CS during interaction between Arabidopsis plants and two sedentary root-parasitic nematode species, the cyst nematode Heterodera schachtii and the root-knot nematode Meloidogyne incognita. We found that nematode infection damages the Endodermis leading to the activation of suberin biosynthesis genes at nematode infection sites. Although feeding sites induced by both cyst and root-knot nematodes are surrounded by Endodermis during early stages of infection, the Endodermis is degraded during later stages of feeding site development, indicating periderm formation or ectopic suberization of adjacent tissue. Chemical suberin analysis showed a characteristic suberin composition resembling peridermal suberin in nematode-infected tissue. Notably, infection assays using Arabidopsis lines with CS defects and impaired compensatory suberization, revealed that the CS and suberization impact nematode infectivity and feeding site size. Taken together, our work establishes the role of the endodermal barrier system in defence against a soil-borne pathogen.
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The Casparian strip-one ring to bring cell biology to lignification?
Current Opinion in Biotechnology, 2019Co-Authors: Inês C. R. Barbosa, Nelson Rojas-murcia, Niko GeldnerAbstract:Lignin research has long been motivated by the outstanding importance of wood for human societies. The annual, non-woody Arabidopsis thaliana, has nevertheless contributed greatly to our understanding of lignification, due to its unrivalled genetic resources. Arabidopsis is also great for cell and developmental biology, allowing precise imaging and tracking of cell types. Root Endodermis differentiation involves the precise lignification of the Casparian Strip, as an apoplastic barrier; while barrier damage triggers a less localized, compensatory lignification. Transcriptional reprogramming and peptide-induced signalling emerge as promising tools for the study of endodermal lignification. We argue that Endodermis lignification is an attractive model complementary to equally powerful, cellular xylem differentiation systems, as it might better represent the restricted – often localized – lignification seen in non-vascular cells.
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minimum requirements for changing and maintaining Endodermis cell identity in the arabidopsis root
Nature plants, 2018Co-Authors: Colleen Drapek, Peter Marhavý, Niko Geldner, Erin E Sparks, Isaiah Taylor, Tonni Grube Andersen, Jessica H Hennacy, Philip N BenfeyAbstract:Changes in gene regulation during differentiation are governed by networks of transcription factors. The Arabidopsis root Endodermis is a tractable model to address how transcription factors contribute to differentiation. We used a bottom-up approach to understand the extent to which transcription factors that are required for Endodermis differentiation can confer Endodermis identity to a non-native cell type. Our results show that the transcription factors SHORTROOT and MYB36 alone have limited ability to induce ectopic endodermal features in the absence of additional cues. The stele-derived signalling peptide CIF2 stabilizes SHORTROOT-induced Endodermis identity acquisition. The outcome is a partially impermeable barrier deposited in the subepidermal cell layer, which has a transcriptional signature similar to the Endodermis. These results demonstrate that other root cell types can be forced to differentiate into the Endodermis and highlight a previously unappreciated role for receptor kinase signalling in maintaining Endodermis identity.
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minimum requirements for reprogramming and maintaining cell fate in the arabidopsis root
bioRxiv, 2017Co-Authors: Colleen Drapek, Peter Marhavý, Niko Geldner, Erin E Sparks, Tonni Grube Andersen, Jessica H Hennacy, Philip N BenfeyAbstract:Changes in gene regulation during differentiation are governed by networks of transcription factors. To identify the minimal network for endodermal differentiation in the Arabidopsis root, we asked what transcription factors are sufficient to program a non-native cell-type into Endodermis. Our results show the transcription factors SHORTROOT and MYB36 have limited ability to reprogram a non-native cell-type (the epidermis) and that this reprogramming is reversible in the absence of additional cues. The stele-derived signaling peptide CIF2 stabilizes SHORTROOT-induced reprogramming. The outcome is a partially impermeable barrier deposited in the sub-epidermal cell layer that has a transcriptional signature similar to Endodermis. The trans-differentiation mechanism depends on the expression of genes downstream in the gene regulatory network but is independent of SHORTROOT movement. These results highlight a non cell-autonomous induction mechanism for Endodermis that resembles differentiation in many animal systems.
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The Endodermis, a tightly controlled barrier for nutrients.
Current Opinion in Plant Biology, 2017Co-Authors: Verónica G. Doblas, Niko Geldner, Marie BarberonAbstract:Plant roots acquire nutrients from the soil and transport them upwards to the aerial parts. To reach the central vasculature of the root, water and nutrients radially cross all external cell layers. The Endodermis surrounds the vascular tissues and forms diffusion barriers. It thereby compartmentalizes the root and allows control of nutrient transport from the soil to the vasculature, as well as preventing backflow of nutrients from the stele. To achieve this role, endodermal cells undergo two specialized differentiations states consisting of deposition of two impermeable polymers in the cell wall: lignin, forming the Casparian strips, and suberin lamellae. Recent publications showed that endodermal barrier formation is not a hard-wired, irreversible process. Synthesis and degradation of suberin lamellae is highly regulated by plant hormones in response to nutrient stresses. Moreover, Casparian strip continuity seems to be constantly checked by two small peptides produced in the vasculature that diffuse into the apoplastic space in order to test endodermal barrier integrity. This review discusses the recent understanding of endodermal barrier surveillance and plasticity and its role in plant nutrition.
Daryl E Enstone - One of the best experts on this subject based on the ideXlab platform.
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root Endodermis and exodermis structure function and responses to the environment
Journal of Plant Growth Regulation, 2002Co-Authors: Daryl E Enstone, Carol A. PetersonAbstract:Roots of virtually all vascular plants have an Endodermis with a Casparian band, and the majority of angiosperm roots tested also have an exodermis with a Casparian band. Both the Endodermis and exodermis may develop suberin lamellae and thick, tertiary walls. Each of these wall modifications has its own function(s). The endodermal Casparian band prevents the unimpeded movement of apoplastic substances into the stele and also prevents the backflow of ions that have moved into the stele symplastically and then were released into its apoplast. In roots with a mature exodermis, the barrier to apoplastic inflow of ions occurs near the root surface, but prevention of backflow of ions from the stele remains a function of the Endodermis. The suberin lamellae protect against pathogen invasion and possibly root drying during times of stress. Tertiary walls of the Endodermis and exodermis are believed to function in mechanical support of the root, but this idea remains to be tested. During stress, root growth rates decline, and the Endodermis and exodermis develop closer to the root tip. In two cases, stress is known to induce the formation of an exodermis, and in several other cases to accelerate the development of both the exodermis and Endodermis. The responses of the Endodermis and exodermis to drought, exposure to moist air, flooding, salinity, ion deficiency, acidity, and mechanical impedance are discussed.
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development of the Endodermis and hypodermis of typha glauca godr and typha angustifolia l roots
Botany, 1999Co-Authors: James L. Seago, Carol A. Peterson, Daryl E Enstone, Chris A ScholeyAbstract:The development of the Endodermis and hypodermis in adventitious roots of Typha angustifolia L. and Typha glauca Godr. was followed from the apical meristem to full maturity. The Endodermis was typical, developing a thin Casparian band near the root tip, followed by suberin lamellae and asymmetric, secondary, lignified walls (C-type at maturity). Passage cells were present at an intermediate stage but eventually disappeared when all cells developed lamellae and secondary walls. The hypodermis was multiple (four to six layers at maturity) and began differentiating near the root tip. Here, the radial and transverse walls of the outermost layer did not dissolve in strong acid and the former were wavy in the longitudinal direction, both features characteristic of a Casparian band, but these walls were permeable to berberine. No other indication of a wall modification was seen for 3 weeks, at which time the root had become determinate and aerenchyma was beginning to form in the midcortex. Casparian bands, whic...
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functions of passage cells in the Endodermis and exodermis of roots
Physiologia Plantarum, 1996Co-Authors: Carol A. Peterson, Daryl E EnstoneAbstract:Passage cells frequently occur in the Endodermis and exodermis but are not ubiquitous in either layer. Passage cells occur in the form of short cells in the dimorphic type of exodermis. In both layers, Casparian bands are formed in all cells, but the subsequent development of suberin lamellae and thick, cellulosic walls are delayed or absent in the passage cells. Available evidence suggests that passage cells of the Endodermis are important for the transfer of calcium and magnesium into the stele and thus into the transpiration stream. They become the only cells which present a plasmalemma surface to the soil solution (and are thus capable of ion uptake) when the epidermis and central cortex die. This occurs naturally in some herbaceous and woody species and is known to be promoted by drought. Most evidence indicates that the development of suberin lamellae in both the Endodermis and exodermis increases the resistance of the root to the radial flow of water. Passage cells thus provide areas of low resistance for the movement of water, and the position of these cells in the Endodermis (i.e., in close proximity to the xylem) is explained in terms of function. Exodermal passage cells have a cytoplasmic structure suggesting an active role in ion uptake. This may be related to the tendency of the epidermis to die, leaving the passage cells as the only ones with their membranes exposed to the soil solution. Passage cells in the exodermis attract endomycorrhizal fungi while those in the Endodermis do not. It is clear that passage cells of the Endodermis and exodermis play a variety of roles in the plant root system.
Masao Tasaka - One of the best experts on this subject based on the ideXlab platform.
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Regulation of inflorescence architecture by intertissue layer ligand-receptor communication between Endodermis and phloem
Proceedings of the National Academy of Sciences, 2012Co-Authors: Naoyuki Uchida, R. J. Horst, H.-h. Lai, Ryoko Kajita, Masao Tasaka, Takashi Kakimoto, J S Lee, Keiko U ToriiAbstract:Multicellular organisms achieve final body shape and size by coordinating cell proliferation, expansion, and differentiation. Loss of function in the Arabidopsis ERECTA (ER) receptor-kinase gene confers characteristic compact inflorescence architecture, but its underlying signaling pathways remain unknown. Here we report that the expression of ER in the phloem is sufficient to rescue compact er inflorescences. We further identified two Epidermal Patterning Factor-like (EPFL) secreted peptide genes, EPFL4 and EPFL6/CHALLAH (CHAL), as redundant, upstream components of ER-mediated inflorescence growth. The expression of EPFL4 or EPFL6 in the Endodermis, a layer adjacent to phloem, is sufficient to rescue the er-like inflorescence of epfl4 epfl6 plants. EPFL4 and EPFL6 physically associate with ER in planta. Finally, transcriptome analysis of er and epfl4 epfl6 revealed a potential downstream component as well as a role for plant hormones in EPFL4/6- and ER-mediated inflorescence growth. Our results suggest that intercell layer communication between the Endodermis and phloem mediated by peptide ligands and a receptor kinase coordinates proper inflorescence architecture in Arabidopsis.
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Amyloplasts and Vacuolar Membrane Dynamics in the Living Graviperceptive Cell of the Arabidopsis Inflorescence Stem
The Plant cell, 2005Co-Authors: Chieko Saito, Takehide Kato, Miyo Terao Morita, Masao TasakaAbstract:We developed an adequate method for the in vivo analysis of organelle dynamics in the gravity-perceptive cell (Endodermis) of the Arabidopsis thaliana inflorescence stem, revealing behavior of amyloplasts and vacuolar membranes in those cells. Amyloplasts in the Endodermis showed saltatory movements even before gravistimulation by reorientation, and these movements were confirmed as microfilament dependent. From our quantitative analysis in the wild type, the gravity-oriented movement of amyloplasts mainly occurred during 0 to 3 min after gravistimulation by reorientation, supporting findings from our previous physiological study. Even after microfilament disruption, the gravity-oriented movement of amyloplasts remained. By contrast, in zig/sgr4 mutants, where a SNARE molecule functioning in vacuole biogenesis has been disrupted, the movement of amyloplasts in the Endodermis is severely restricted both before and after gravistimulation by reorientation. Here, we describe vacuolar membrane behavior in these cells in the wild-type, actin filament-disrupted, and zig/sgr4 mutants and discuss its putatively important features for the perception of gravity. We also discuss the data on the two kinds of movements of amyloplasts that may play an important role in gravitropism: (1) the leading edge amyloplasts and (2) the en mass movement of amyloplasts.
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involvement of the vacuoles of the Endodermis in the early process of shoot gravitropism in arabidopsis
The Plant Cell, 2002Co-Authors: Miyo Terao Morita, Takehide Kato, Kiyoshi Nagafusa, Chieko Saito, Akihiko Nakano, Takashi Ueda, Masao TasakaAbstract:The endodermal cells of the shoot are thought to be the gravity-sensing cells in Arabidopsis. The amyloplasts in the Endodermis that sediment in the direction of gravity may act as statoliths. Endodermis-specific expression of SGR2 and ZIG using the SCR promoter could complement the abnormal shoot gravitropism of the sgr2 and zig mutants, respectively. The abnormalities in amyloplast sedimentation observed in both mutants recovered simultaneously. These results indicate that both genes in the endodermal cell layer are crucial for shoot gravitropism. ZIG encodes AtVTI11, which is a SNARE involved in vesicle transport to the vacuole. The fusion protein of SGR2 and green fluorescent protein localized to the vacuole and small organelles. These observations indicate that ZIG and SGR2 are involved in the formation and function of the vacuole, a notion supported by the results of subcellular analysis of the sgr2 and zig mutants with electron microscopy. These results strongly suggest that the vacuole participates in the early events of gravitropism and that SGR2 and ZIG functions are involved.
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the Endodermis and shoot gravitropism
Trends in Plant Science, 1999Co-Authors: Masao Tasaka, Takehide Kato, Hidehiro FukakiAbstract:Abstract Shoots and roots of higher plants exhibit negative and positive gravitropism, respectively. A variety of gravitropic mutants have recently been isolated from Arabidopsis , the characterization of which demonstrates that the molecular mechanisms of the gravitropic responses in roots, hypocotyls and inflorescence stems are different. The cytological and molecular analysis of two mutants, shoot gravitropism 1 ( sgr1 ), which is allelic to scarecrow ( scr ), and sgr7 , which is allelic to short-root ( shr ), indicate that the Endodermis is the site of gravity perception in shoots. These data suggest a new model for shoot gravitropism.
Malcolm J Bennett - One of the best experts on this subject based on the ideXlab platform.
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Endodermal ABA signaling promotes lateral root quiescence during salt stress in Arabidopsis seedlings.
The Plant cell, 2013Co-Authors: Lina Duan, Penny Mei Yeen Chan, Rishikesh Bhalerao, Daniela Dietrich, Malcolm J Bennett, Chong Han Ng, Jose R DinnenyAbstract:The endodermal tissue layer is found in the roots of vascular plants and functions as a semipermeable barrier, regulating the transport of solutes from the soil into the vascular stream. As a gateway for solutes, the Endodermis may also serve as an important site for sensing and responding to useful or toxic substances in the environment. Here, we show that high salinity, an environmental stress widely impacting agricultural land, regulates growth of the seedling root system through a signaling network operating primarily in the Endodermis. We report that salt stress induces an extended quiescent phase in postemergence lateral roots (LRs) whereby the rate of growth is suppressed for several days before recovery begins. Quiescence is correlated with sustained abscisic acid (ABA) response in LRs and is dependent upon genes necessary for ABA biosynthesis, signaling, and transcriptional regulation. We use a tissue-specific strategy to identify the key cell layers where ABA signaling acts to regulate growth. In the Endodermis, misexpression of the ABA insensitive1-1 mutant protein, which dominantly inhibits ABA signaling, leads to a substantial recovery in LR growth under salt stress conditions. Gibberellic acid signaling, which antagonizes the ABA pathway, also acts primarily in the Endodermis, and we define the crosstalk between these two hormones. Our results identify the Endodermis as a gateway with an ABA-dependent guard, which prevents root growth into saline environments.
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auxin reflux between the Endodermis and pericycle promotes lateral root initiation
The EMBO Journal, 2012Co-Authors: Peter Marhavý, Malcolm J Bennett, Tom Beeckman, Bert De Rybel, Marleen Vanstraelen, Ding Zhaojun, Eva BenkovaAbstract:Lateral root (LR) formation is initiated when pericycle cells accumulate auxin, thereby acquiring founder cell (FC) status and triggering asymmetric cell divisions, giving rise to a new primordium. How this auxin maximum in pericycle cells builds up and remains focused is not understood. We report that the Endodermis plays an active role in the regulation of auxin accumulation and is instructive for FCs to progress during the LR initiation (LRI) phase. We describe the functional importance of a PIN3 (PIN-formed) auxin efflux carrier-dependent hormone reflux pathway between overlaying endodermal and pericycle FCs. Disrupting this reflux pathway causes dramatic defects in the progress of FCs towards the next initiation phase. Our data identify an unexpected regulatory function for the Endodermis in LRI as part of the fine-tuning mechanism that appears to act as a check point in LR organogenesis after FCs are specified.
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Gibberellin Signaling in the Endodermis Controls Arabidopsis Root Meristem Size
Current biology : CB, 2009Co-Authors: Susana Ubeda-tomás, Ranjan Swarup, Gerrit T S Beemster, Fernán Federici, Ilda Casimiro, Peter Doerner, Jim Haseloff, Malcolm J BennettAbstract:Plant growth is driven by cell proliferation and elongation. The hormone gibberellin (GA) regulates Arabidopsis root growth by controlling cell elongation, but it is currently unknown whether GA also controls root cell proliferation. Here we show that GA biosynthetic mutants are unable to increase their cell production rate and meristem size after germination. GA signals the degradation of the DELLA growth repressor proteins GAI and RGA, promoting root cell production. Targeting the expression of gai (a non-GA-degradable mutant form of GAI) in the root meristem disrupts cell proliferation. Moreover, expressing gai in dividing endodermal cells was sufficient to block root meristem enlargement. We report a novel function for GA regulating cell proliferation where this signal acts by removing DELLA in a subset of, rather than all, meristem cells. We suggest that the GA-regulated rate of expansion of dividing endodermal cells dictates the equivalent rate in other root tissues. Cells must double in size prior to dividing but cannot do so independently, because they are physically restrained by adjacent tissues with which they share cell walls. Our study highlights the importance of probing regulatory mechanisms linking molecular- and cellular-scale processes with tissue and organ growth responses.