Lateral Root Development In Arabidopsis Research Articles

Interaction between glucose and brassinosteroid during the regulation of lateral root development in Arabidopsis.

Glucose (Glc) plays a fundamental role in regulating lateral root (LR) development as well as LR emergence. In this study, we show that brassinosteroid (BR) signaling works downstream of Glc in controlling LR production/emergence in Arabidopsis (Arabidopsis thaliana) seedlings. Glc and BR can promote LR emergence at lower concentrations, while at higher concentrations, both have an inhibitory effect. The BR biosynthesis and perception mutants showed highly reduced numbers of emerged LRs at all the Glc concentrations tested. BR signaling works downstream of Glc signaling in regulating LR production, as in the glucose insensitive2-1brassinosteroid insensitive1 double mutant, Glc-induced LR production/emergence was severely reduced. Differential auxin distribution via the influx carriers AUXIN RESISTANT1/LIKE AUXIN RESISTANT1-3 and the efflux carrier PIN-FORMED2 plays a central role in controlling LR production in response to Glc and BR. Auxin signaling components AUXIN RESISTANT2,3 and SOLITARY ROOT act downstream of Glc and BR. AUXIN RESPONSE FACTOR7/19 work farther downstream and control LR production by regulating the expression of LATERAL ORGAN BOUNDARIES-DOMAIN29 and EXPANSIN17 genes. Increasing light flux could also mimic the Glc effect on LR production/emergence. However, increased light flux could not affect LR production in those BR and auxin signaling mutants that were defective for Glc-induced LR production. Altogether, our study suggests that, under natural environmental conditions, modulation of endogenous sugar levels can manipulate root architecture for optimized development by altering its nutrient/water uptake as well as its anchorage capacity.

AtMYB93 is a novel negative regulator of lateral root development in Arabidopsis.

Plant root system plasticity is critical for survival in changing environmental conditions. One important aspect of root architecture is lateral root development, a complex process regulated by hormone, environmental and protein signalling pathways.Here we show, using molecular genetic approaches, that the MYB transcription factor AtMYB93 is a novel negative regulator of lateral root development in Arabidopsis.We identify AtMYB93 as an interaction partner of the lateral-root-promoting ARABIDILLO proteins. Atmyb93 mutants have faster lateral root developmental progression and enhanced lateral root densities, while AtMYB93-overexpressing lines display the opposite phenotype. AtMYB93 is expressed strongly, specifically and transiently in the endodermal cells overlying early lateral root primordia and is additionally induced by auxin in the basal meristem of the primary root. Furthermore, Atmyb93 mutant lateral root development is insensitive to auxin, indicating that AtMYB93 is required for normal auxin responses during lateral root development.We propose that AtMYB93 is part of a novel auxin-induced negative feedback loop stimulated in a select few endodermal cells early during lateral root development, ensuring that lateral roots only develop when absolutely required. Putative AtMYB93 homologues are detected throughout flowering plants and represent promising targets for manipulating root systems in diverse crop species.

AtMYB93 is an endodermis-specific transcriptional regulator of lateral root development in Arabidopsis

AtMYB93 is an endodermis-specific transcriptional regulator of lateral root development in Arabidopsis

The AP2/EREBP Gene PUCHI Co-Acts with LBD16/ASL18 and LBD18/ASL20 Downstream of ARF7 and ARF19 to Regulate Lateral Root Development in Arabidopsis

The developmental process of lateral root formation consists of priming, initiation, primordium development and the emergence of lateral roots from the primary root. Molecular genetic studies with Arabidopsis have revealed several key transcriptional regulators involved in lateral root development. However, their functional interaction has not been fully characterized yet. Here we utilized a genetic approach to understand some of these interactions, revealing that PUCHI functioning in morphogenesis of early lateral root primordium is regulated downstream of ARF7/ARF19 and acts with LBD16(ASL18)/LBD18(ASL20) to regulate lateral root development. We showed that auxin-responsive expression of PUCHI was significantly reduced in arf7 or arf19 single mutants and completely abolished in arf7 arf19 double mutants. Consistent with this, β-glucuronidase (GUS) expression under the PUCHI promoter in arf7 arf19 was greatly reduced in the lateral root primordium compared with that in the wild type and did not respond to exogenous auxin. Results of GUS expression analyses under the PUCHI, LBD16 or LBD18 promoter in lbd16, lbd18 single and double mutants or puchi demonstrated that PUCHI and LBD16 or LBD18 do not regulate each other's expression. Lateral root phenotypes of double and triple mutants of lbd16, lbd18 and puchi showed that the puchi mutation in lbd16 and lbd18 mutants synergistically decreased the number of emerged lateral roots. These analyses also showed that puchi affected lateral root primordium development of lbd16 or lbd18 additively but differentially. Taken together, these results suggest that PUCHI co-acts with LBD16 and LBD18 to control lateral root primordium development and lateral root emergence.

Lateral root development in Arabidopsis: fifty shades of auxin

The developmental plasticity of the root system represents a key adaptive trait enabling plants to cope with abiotic stresses such as drought and is therefore important in the current context of global changes. Root branching through lateral root formation is an important component of the adaptability of the root system to its environment. Our understanding of the mechanisms controlling lateral root development has progressed tremendously in recent years through research in the model plant Arabidopsis thaliana (Arabidopsis). These studies have revealed that the phytohormone auxin acts as a common integrator to many endogenous and environmental signals regulating lateral root formation. Here, we review what has been learnt about the myriad roles of auxin during lateral root formation in Arabidopsis.

OPR3 is expressed in phloem cells and is vital for lateral root development in Arabidopsis

Li, S., Ma, J. and Liu, P. 2013. OPR3 is expressed in phloem cells and is vital for lateral root development in Arabidopsis. Can. J. Plant Sci. 93: 165–170. Jasmonates, a group of oxylipin phytohormones in angiosperms, play important roles in regulating plant growth and development and in responding to environmental stimuli. AtOPR3, a 12-oxo-phytodienoic acid (OPDA) reductase in Arabidopsis thaliana, has been proven to be vital in catalyzing jasmonate biosynthesis. Here, the temporal and spatial expression of AtOPR3 was investigated by promoter-GUS fusion in A. thaliana. In pOPR3::GUS transgenic plants, the GUS activity was detected in roots, leaves and all floral organs, and was highly induced by MeJA treatment. In addition, the GUS activity was principally detected in the phloem cells of the leaf veins. The sequence of the OPR3 promoter region was predicted to have 49 potential binding sites for transcription factors including the well-known Myc-like basic helix-loop-helix, GATA, MADS, MYB-like and Homeobox proteins. In consistent with an expression of OPR3 in lateral roots, there are more lateral roots in the opr3 mutant plants, in which OPR3 expression is knocking-out. In addition, the involvement of auxin biosynthesis in JA-regulated lateral root development is implied by our observation that the transcripts of ASA1, a gene involved in auxin biosynthesis, are decreased in opr3 plants.

MiRNA164-directed cleavage of ZmNAC1 confers lateral root development in maize (Zea maysL.)

BackgroundMicroRNAs are a class of small, non-coding RNAs that regulate gene expression by binding target mRNA, which leads to cleavage or translational inhibition. The NAC proteins, which include NAM, ATAF, and CUC, are a plant-specific transcription factor family with diverse roles in development and stress regulation. It has been reported that miR164 negatively regulates NAC1 expression, which in turn affects lateral root development in Arabidopsis; however, little is known about the involvement of the maize NAC family and miR164 in lateral root development.ResultsWe collected 175 maize transcripts with NAC domains. Of these, 7 ZmNACs were putative targets for regulation by miR164. We isolated one gene, called TC258020 (designated ZmNAC1) from 2 maize inbred lines, 87-1 and Zong3. ZmNAC1 had a high expression level in roots and showed higher abundance (1.8 fold) in Zong3 relative to 87-1, which had less lateral roots than Zong3. There was a significant correlation between the expression level of ZmNAC1 and the lateral root density in the recombinant inbred line (RIL) population. Transgenic Arabidopsis that overexpressed ZmNAC1 had increased lateral roots in comparison to the wild type. These findings suggest that ZmNAC1 played a significant role in lateral root development. An allelic expression assay showed that trans-regulatory elements were the dominant mediators of ZmNAC1 differential expression in 87-1 and Zong3, and further analysis revealed that miR164 was a trans-element that guided the cleavage of endogenous ZmNAC1 mRNA. Both mature miR164 and miR164 precursors had higher expression in 87-1 than Zong3, which was the opposite of the expression pattern of ZmNAC1. Additionally, the allelic assay showed that the cis-regulatory element most likely affected Zm-miR164b's expression pattern. A β-glucuronidase (GUS) assay showed that the Zm-miR164b promoter had higher GUS activity in 87-1 than in Zong3. In addition, we detected miR164b expression in the RIL population, and the results indicated that miR164b had a higher expression level in the RILs containing 87-1 promoter than those containing Zong3 promoter.ConclusionOur results indicate one possible pathway in maize by which differences in miR164b promoter activity resulted in a different expression pattern for mature miR164 which negatively regulates ZmNAC1 expression in 87-1 and Zong3, thereby contributing to a significantly different lateral root phenotype.

Hormonal Regulation of Lateral Root Development in Arabidopsis Modulated byMIZ1and Requirement of GNOM Activity forMIZ1Function

Plant organ development is important for adaptation to a changing environment. Genetic and physiological studies have revealed that plant hormones play key roles in lateral root formation. In this study, we show that MIZU-KUSSEI1 (MIZ1), which was identified originally as a regulator of hydrotropism, functions as a novel regulator of hormonally mediated lateral root development. Overexpression of MIZ1 (MIZ1OE) in roots resulted in a reduced number of lateral roots being formed; however, this defect could be recovered with the application of auxin. Indole-3-acetic acid quantification analyses showed that free indole-3-acetic acid levels decreased in MIZ1OE roots, which indicates that alteration of auxin level is critical for the inhibition of lateral root formation in MIZ1OE plants. In addition, MIZ1 negatively regulates cytokinin sensitivity on root development. Application of cytokinin strongly induced the localization of MIZ1-green fluorescent protein to lateral root primordia, which suggests that the inhibition of lateral root development by MIZ1 occurs downstream of cytokinin signaling. Surprisingly, miz2, a weak allele of gnom, suppressed developmental defects in MIZ1OE plants. Taken together, these results suggest that MIZ1 plays a role in lateral root development by maintaining auxin levels and that its function requires GNOM activity. These data provide a molecular framework for auxin-dependent organ development in Arabidopsis (Arabidopsis thaliana).

Arabidopsis Lateral Root Development 3 is essential for early phloem development and function, and hence for normal root system development

We have identified a gene, Lateral Root Development 3 (LRD3), that is important for maintaining a balance between primary and lateral root growth. The lrd3 mutant has decreased primary root growth and increased lateral root growth. We determined that the LRD3 gene encodes a LIM-domain protein of unknown function. LRD3 is expressed only in the phloem companion cells, which suggested a role in phloem function. Indeed, while phloem loading and export from the shoot appear to be normal, delivery of phloem to the primary root tip is limited severely in young seedlings. Abnormalities in phloem morphology in these seedlings indicate that LRD3 is essential for correct early phloem development. There is a subsequent spontaneous recovery of normal phloem morphology, which is correlated tightly with increased phloem delivery and growth of the primary root. The LRD3 gene is one of very few genes described to affect phloem development, and the only one that is specific to early phloem development. Continuous growth on auxin also leads to recovery of phloem development and function in lrd3, which demonstrates that auxin plays a key role in early phloem development. The root system architecture and the pattern of phloem allocation in the lrd3 root system suggested that there may be regulated mechanisms for selectively supporting certain lateral roots when the primary root is compromised. Therefore, this study provides new insights into phloem-mediated resource allocation and its effects on plant root system architecture.

Rice Gene OsDSR-1 Promotes Lateral Root Development in Arabidopsis Under High-Potassium Conditions

Rice gene Oryza sativa Drought Stress Response-1 (OsDSR-1) was one of the genes identified to be responsive to drought stress in the panicle of rice at booting and heading stages by both microarray and quantitative real-time PCR analyses. OsDSR-1 encodes a putative calcium-binding protein, and its overexpression in Arabidopsis rendered transgenic plants to produce much shorter lateral roots (LRs) than wild-type (WT) plants in the medium supplemented with abscisic acid (ABA), suggesting that OsDSR-1 may act as a positive regulator during the process of ABA inhibition of LR development. No significant difference was observed in the total LR length between WT and transgenic plants in the media with the increase of only osmotic stress caused by NaCl, LiCl, and mannitol, while transgenic Arabidopsis seedlings appeared to produce larger root systems with longer total LR lengths under high-potassium conditions than WT seedlings. Further analysis showed that external Ca2+ was required for the production of larger root systems, indicating that the promotion by OsDSR-1 of the LR development of transgenic Arabidopsis seemed to occur in a Ca2+-dependent manner under high-potassium conditions. We propose that OsDSR-1 may function as a calcium sensor of the signal transduction pathway controlling the LR development under high-potassium conditions.

Plant Development: Early Events in Lateral Root Initiation

How are the lateral root founder cells specified in the pericycle to initiate lateral root development? An Aux/IAA28 signaling module activates transcription factor GATA23 to control founder cell identity.

F-box Protein Arabidillo-1 Promotes Lateral Root Development by Depressing the Functioning of GA3 in Arabidopsis

In Arabidopsis, Arabidillo-1 and Arabidillo-2 have great sequence homology to Dictyostelium and metazoan β–catenin/Armadillo, which are important to animal and Dictyostelium development. Arabidillo-1 and Arabidillo-2 promote lateral root formation redundantly in Arabidopsis. Here, we showed that gibberellins (GA3) has a greater inhibitory effect on lateral root growth from the null mutant arabidillo-1 than from the wild type, suggesting that the mechanism for Arabidillo-1-regulated modulation of lateral root proliferation is associated with GA3-metabolic or signaling pathways. Our yeast two-hybrid analysis demonstrated that Arabidillo-1 interacts with ASK2 and ASK11, and that ASK2 can bind with the F-box domain of Arabidillo-1. Therefore, Arabidillo-1 is involved in the ubiquitin/26S proteasome-mediated proteolytic pathway. Based on these results, we conclude that Arabidillo-1 can degrade some positive regulator of the GA3 signaling pathway through selective protein degradation of ubiquitin/26S. Moreover, that process is believed to be the mechanism for Arabidillo-1 promotion of lateral root development in Arabidopsis.

Nitric Oxide is Involved in Alkamide-Induced Lateral Root Development in Arabidopsis

Alkamides are small bioactive lipid signals with a wide distribution in plants. In this report, the role of nitric oxide (NO) in the alterations induced by N-isobutyl decanamide on the Arabidopsis (Arabidopsis thaliana) root system architecture (RSA) was investigated. We first compared the effects of N-isobutyl decanamide and NO donors sodium nitropruside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) on root morphogenetic processes. Both N-isobutyl decanamide and NO donors modulated RSA in a similar way and in a dose-dependent manner, inhibiting primary root growth and promoting lateral root primordia (LRP) formation. RSA alterations induced by N-isobutyl decanamide correlated with NO accumulation in the primary root tip and in developing lateral roots. Morphogenetic effects of N-isobutyl decanamide decreased when NO scavengers were supplied to alkamide-treated seedlings. N-Isobutyl decanamide-regulated root architectural changes were also investigated in mutants defective in NO biosynthesis, nia1 nia2, and NO signalling, Atnoa1, and in the alkamide-resistant mutant drr1. The nia1 nia2 and Atnoa1 mutants were indistinguishable in primary root growth inhibition by the alkamide when compared with wild-type (WT) seedlings, but showed reduced lateral root responses. The drr1 mutant was less sensitive in both primary root growth inhibition and LRP induction by NO donors than WT seedlings. Detailed DR5:uidA and BA3:uidA marker analysis showed that N-isobutyl decanamide and its interacting signals jasmonic acid and NO act downstream or independently of auxin-responsive gene expression to promote LRP formation. Our results provide compelling evidence that NO is an intermediate in alkamide signaling mediating RSA adjustment in Arabidopsis.

Multimodular auxin response controls lateral root development in Arabidopsis

In plants, the phytohormone auxin plays a prominent role in controlling nearly every step in plant growth and development. However, it is unclear how one generic signal such as auxin can be translated in so many diverse developmental responses. Recently, we could show that, next to its well known role in embryogenesis, the auxin response module controlled by the BODENLOS (BDL)/INDOLE-3-ACETIC ACID12 (IAA12)-MONOPTEROS (MP)/AUXIN RESPONSE FACTOR5 (ARF5) pair also plays a role in lateral root development, and that this auxin response succeeds the one controlled by SOLITARY ROOT (SLR)/IAA14-ARF7-ARF19. We conclude that bi- or multimodular response mechanisms might be a general principle of auxin signaling in plants, which provides a genetic framework for a single molecule such as auxin to have many diverse functions.

Auxin and Abscisic Acid Responses of Auxin Response Factor 3 in Arabidopsis Lateral Root Development

As in the cases of the embryo and many lateral organs, lateral root (LR) development is triggered by the phytohormone auxin. LR development is also known to be inhibited by abscisic acid (ABA). Here we show that an auxin response factor ARF3, which participates in pattern formation of aerial lateral organs, such as leaf or flower, is up-regulated by auxin during LR development in Arabidopsis. This study demonstrates that ARF3 expression is regulated at the transcriptional level and by posttranscriptional gene silencing (PTGS), which is mediated by a group of transacting small-interfering RNA (tasiRNA-ARF). The tasiRNA-ARF pathway and ARF3 expression are sensitive to auxin and ABA treatment, suggesting that tasiRNA-ARF-dependent PTGS of ARF3 is linked to auxin promotion of LR development and to ABA inhibition.

Auxin regulation of the microRNA390-dependent transacting small interfering RNA pathway in Arabidopsis lateral root development

MicroRNA (miR)390 cleaves the non-coding TAS3 precursor RNA for the production of tasiRNA-ARF, a group of an endogenous trans-acting small-interfering RNAs which cleave the transcripts of auxin response factor (ARF) 3/4. miR390-cleaved TAS3 RNA is polymerized and diced into tasiRNA-ARF by RNA-dependent RNA polymerase6 (RDR6) and Dicer-like4 (DCL4), respectively. tasiRNA-ARF-dependent post-transcriptional gene silencing (PTGS) of ARF3/4 is involved in auxin-mediated polarity establishment in the development of aerial lateral organs, such as leaf and flower. To understand how auxin regulates ARF4 expression, we examined auxin responsiveness of miR390 expression, which comprises a regulatory step for the biogenesis pathway of tasiRNA-ARF (the tasiRNA-ARF pathway), in Arabidopsis thaliana lateral root (LR) development. The results of this study provide evidence that miR390 expression is sensitive to TIR1-dependent transcriptional regulation and auxin concentration, and also that mutual negative-regulation between the tasiRNA-ARF pathway and ARF4 modulates the spatiotemporal expression of ARF4. We propose that, together with auxin concentration sensing through miR390 transcription, the tasiRNA-ARF pathway mediates the auxin response and ARF4-mediated LR developmental processes.

Phosphate availability alters lateral root development in Arabidopsis by modulating auxin sensitivity via a mechanism involving the TIR1 auxin receptor.

The survival of plants, as sessile organisms, depends on a series of postembryonic developmental events that determine the final architecture of plants and allow them to contend with a continuously changing environment. Modulation of cell differentiation and organ formation by environmental signals has not been studied in detail. Here, we report that alterations in the pattern of lateral root (LR) formation and emergence in response to phosphate (Pi) availability is mediated by changes in auxin sensitivity in Arabidopsis thaliana roots. These changes alter the expression of auxin-responsive genes and stimulate pericycle cells to proliferate. Modulation of auxin sensitivity by Pi was found to depend on the auxin receptor TRANSPORT INHIBITOR RESPONSE1 (TIR1) and the transcription factor AUXIN RESPONSE FACTOR19 (ARF19). We determined that Pi deprivation increases the expression of TIR1 in Arabidopsis seedlings and causes AUXIN/INDOLE-3-ACETIC ACID (AUX/IAA) auxin response repressors to be degraded. Based on our results, we propose a model in which auxin sensitivity is enhanced in Pi-deprived plants by an increased expression of TIR1, which accelerates the degradation of AUX/IAA proteins, thereby unshackling ARF transcription factors that activate/repress genes involved in LR formation and emergence.

Cytokinins Act Directly on Lateral Root Founder Cells to Inhibit Root Initiation

In Arabidopsis thaliana, lateral roots are formed from root pericycle cells adjacent to the xylem poles. Lateral root development is regulated antagonistically by the plant hormones auxin and cytokinin. While a great deal is known about how auxin promotes lateral root development, the mechanism of cytokinin repression is still unclear. Elevating cytokinin levels was observed to disrupt lateral root initiation and the regular pattern of divisions that characterizes lateral root development in Arabidopsis. To identify the stage of lateral root development that is sensitive to cytokinins, we targeted the expression of the Agrobacterium tumefaciens cytokinin biosynthesis enzyme isopentenyltransferase to either xylem-pole pericycle cells or young lateral root primordia using GAL4-GFP enhancer trap lines. Transactivation experiments revealed that xylem-pole pericycle cells are sensitive to cytokinins, whereas young lateral root primordia are not. This effect is physiologically significant because transactivation of the Arabidopsis cytokinin degrading enzyme cytokinin oxidase 1 in lateral root founder cells results in increased lateral root formation. We observed that cytokinins perturb the expression of PIN genes in lateral root founder cells and prevent the formation of an auxin gradient that is required to pattern lateral root primordia.

Armadillo-related proteins promote lateral root development in Arabidopsis

Armadillo/beta-catenin and related proteins have important functions during animal and Dictyostelium development, regulating cell differentiation, proliferation, and adhesion. Armadillo-repeat-containing proteins also exist in plants, but the majority have unknown roles. The Arabidopsis genes that show greatest sequence homology to Armadillo/beta-catenin are called ARABIDILLO-1 and -2. Here, we demonstrate that ARABIDILLO-1 and -2 promote lateral root development. arabidillo-1/-2 mutants form fewer lateral roots, and ARABIDILLO-1-overexpressing lines produce more lateral roots than wild-type seedlings. ARABIDILLO-yellow fluorescent protein fusions are nuclear. ARABIDILLO proteins contain an F-box motif, and thus may target other proteins for proteasomal degradation. Overexpression of ARABIDILLO-1 protein fragments, including F-box fragments, in wild-type seedlings reduces lateral root formation to the level of the arabidillo-1/-2 mutant. We have shown that plant beta-catenin-related proteins regulate root development. We suggest that ARABIDILLO proteins may target an inhibitor of lateral root development for degradation and propose that Arabidopsis beta-catenin-related proteins define a previously uncharacterized pathway that promotes root branching.

Tissue‐specific expression of stabilized SOLITARY‐ROOT/IAA14 alters lateral root development in Arabidopsis

Auxin is important for lateral root (LR) initiation and subsequent LR primordium development. However, the roles of tissue-specific auxin signaling in these processes are poorly understood. We analyzed transgenic Arabidopsis plants expressing the stabilized mutant INDOLE-3 ACETIC ACID 14 (IAA14)/SOLITARY-ROOT (mIAA14) protein as a repressor of the auxin response factors (ARFs), under the control of tissue-specific promoters. We showed that plants expressing the mIAA14-glucocorticoid receptor (GR) fusion protein under the control of the native IAA14 promoter had the solitary-root/iaa14 mutant phenotypes, including the lack of LR formation under dexamethasone (Dex) treatment, indicating that mIAA14-GR is functional in the presence of Dex. We then demonstrated that expression of mIAA14-GR under the control of the stele-specific SHORT-ROOT promoter suppressed LR formation, and showed that mIAA14-GR expression in the protoxylem-adjacent pericycle also blocked LR formation, indicating that the normal auxin response mediated by auxin/indole-3 acetic acid (Aux/IAA) signaling in the protoxylem pericycle is necessary for LR formation. In addition, we demonstrated that expression of mIAA14-GR under either the ARF7 or the ARF19 promoter also suppressed LR formation as in the arf7 arf19 double mutants, and that IAA14 interacted with ARF7 and ARF19 in yeasts. These results strongly suggest that mIAA14-GR directly inactivates ARF7/ARF19 functions, thereby blocking LR formation. Post-embryonic expression of mIAA14-GR under the SCARECROW promoter, which is expressed in the specific cell lineage during LR primordium formation, caused disorganized LR development. This indicates that normal auxin signaling in LR primordia, which involves the unknown ARFs and Aux/IAAs, is necessary for the establishment of LR primordium organization. Thus, our data show that tissue-specific expression of a stabilized Aux/IAA protein allows analysis of tissue-specific auxin responses in LR development by inactivating ARF functions.