BACKGROUND AND AIMS: The maize lrt1 (lateral rootless1) mutant is impaired in its development of lateral roots during early post-embryonic development. The aim of this study was to characterize, in detail, the influences that the mutation exerts on lateral root initiation and the subsequent developments, as well as to describe the behaviour of the entire plant under variable environmental conditions. METHODS: Mutant lrt1 plants were cultivated under different conditions of hydroponics, and in between sheets of moist paper. Cleared whole mounts and anatomical sections were used in combination with both selected staining procedures and histochemical tests to follow root development. Root surface permeability tests and the biochemical quantification of lignin were performed to complement the structural data. KEY RESULTS: The data presented suggest a redefinition of lrt1 function in lateral roots as a promoter of later development; however, neither the complete absence of lateral roots nor the frequency of their initiation is linked to lrt1 function. The developmental effects of lrt1 are under strong environmental influences. Mutant primordia are affected in structure, growth and emergence; and the majority of primordia terminate their growth during this last step, or shortly thereafter. The lateral roots are impaired in the maintenance of the root apical meristem. The primary root shows disturbances in the organization of both epidermal and subepidermal layers. The lrt1-related cell-wall modifications include: lignification in peripheral layers, the deposition of polyphenolic substances and a higher activity of peroxidase. CONCLUSIONS: The present study provides novel insights into the function of the lrt1 gene in root system development. The lrt1 gene participates in the spatial distribution of initiation, but not in its frequency. Later, the development of lateral roots is strongly affected. The effect of the lrt1 mutation is not as obvious in the primary root, with no influences observed on the root apical meristem structure and maintenance; however, development of the epidermis and cortex are impaired.

• Keywords
• Zea mays, lateral root, lateral root emergence, lignin, lrt1, peroxidase, root apical meristem,
• MeSH
• Cell Wall metabolism   MeSH
• Plant Epidermis anatomy & histology   genetics   growth & development   MeSH
• Hydroponics MeSH
• Plant Roots cytology   genetics   growth & development   MeSH
• Zea mays cytology   genetics   growth & development   MeSH
• Lignin metabolism   MeSH
• Meristem cytology   genetics   growth & development   MeSH
• Mutation MeSH
• Polyphenols metabolism   MeSH
• Gene Expression Regulation, Plant * MeSH
• Plant Proteins genetics   metabolism   MeSH
• Seedlings cytology   genetics   growth & development   MeSH
• Plant Shoots cytology   genetics   growth & development   MeSH
• Gene Expression Regulation, Developmental MeSH
• Environment MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Lignin MeSH
• Polyphenols MeSH
• Plant Proteins MeSH

As non-photosynthesizing organs, roots are dependent on diffusion of oxygen from the external environment and, in some instances, from the shoot for their aerobic metabolism. Establishment of hypoxic niches in the developing tissues of plants has been postulated as a consequence of insufficient diffusion of oxygen to satisfy the demands throughout development. Here, we report that such niches are established at specific stages of lateral root primordia development in Arabidopsis thaliana grown under aerobic conditions. Using gain- and loss-of-function mutants, we show that ERF-VII transcription factors, which mediate hypoxic responses, control root architecture by acting in cells with a high level of auxin signaling. ERF-VIIs repress the expression of the auxin-induced genes LBD16, LBD18, and PUCHI, which are essential for lateral root development, by binding to their promoters. Our results support a model in which the establishment of hypoxic niches in the developing lateral root primordia contributes to the shutting down of key auxin-induced genes and regulates the production of lateral roots.

• Keywords
• Arabidopsis, ERF-VII, auxin, hypoxia, lateral root, root development,
• MeSH
• Arabidopsis cytology   genetics   metabolism   MeSH
• Cell Hypoxia MeSH
• Plant Roots cytology   MeSH
• Indoleacetic Acids metabolism   MeSH
• Arabidopsis Proteins metabolism   MeSH
• Gene Expression Regulation, Plant MeSH
• Signal Transduction * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Indoleacetic Acids MeSH
• Arabidopsis Proteins MeSH

Efficient soil exploration by roots represents an important target for crop improvement and food security [1, 2]. Lateral root (LR) formation is a key trait for optimizing soil foraging for crucial resources such as water and nutrients. Here, we report an adaptive response termed xerobranching, exhibited by cereal roots, that represses branching when root tips are not in contact with wet soil. Non-invasive X-ray microCT imaging revealed that cereal roots rapidly repress LR formation as they enter an air space within a soil profile and are no longer in contact with water. Transcript profiling of cereal root tips revealed that transient water deficit triggers the abscisic acid (ABA) response pathway. In agreement with this, exogenous ABA treatment can mimic repression of LR formation under transient water deficit. Genetic analysis in Arabidopsis revealed that ABA repression of LR formation requires the PYR/PYL/RCAR-dependent signaling pathway. Our findings suggest that ABA acts as the key signal regulating xerobranching. We conclude that this new ABA-dependent adaptive mechanism allows roots to rapidly respond to changes in water availability in their local micro-environment and to use internal resources efficiently.

• Keywords
• Arabidopsis, abscisic acid, auxin, cereal crops, lateral roots, root system architecture, soil air spaces, water deficit,
• MeSH
• Adaptation, Psychological physiology   MeSH
• Arabidopsis genetics   MeSH
• Plants, Genetically Modified MeSH
• Edible Grain growth & development   metabolism   MeSH
• Plant Roots metabolism   MeSH
• Abscisic Acid metabolism   MeSH
• Meristem metabolism   MeSH
• Organogenesis, Plant MeSH
• Arabidopsis Proteins genetics   metabolism   MeSH
• Gene Expression Regulation, Plant genetics   MeSH
• Plant Growth Regulators metabolism   MeSH
• Signal Transduction MeSH
• Transcription Factors metabolism   MeSH
• Water metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Abscisic Acid MeSH
• Arabidopsis Proteins MeSH
• Plant Growth Regulators MeSH
• Transcription Factors MeSH
• Water MeSH

Although the significance of apoplasmic barriers in roots with regards to the uptake of toxic elements is generally known, the contribution of apoplasmic bypasses (ABs) to cadmium (Cd) hyperaccumulation is little understood. Here, we employed a combination of stable isotopic tracer techniques, an ABs tracer, hydraulic measurements, suberin lamellae staining, metabolic inhibitors, and antitranspirants to investigate and quantify the impact of the ABs on translocation of Cd to the xylem in roots of a hyperaccumulating (H) ecotype and a non-hyperaccumulating (NH) ecotype of Sedum alfredii. In the H ecotype, the Cd content in the xylem sap was proportional to hydrostatic pressure, which was attributed to pressure-driven flow via the ABs. The contribution of the ABs to Cd transportation to the xylem was dependent on the Cd concentration applied to the H ecotype (up to 37% at the highest concentration used). Cd-treated H ecotype roots showed significantly higher hydraulic conductance compared with the NH ecotype (76 vs 52 × 10–8 m s–1MPa–1), which is in accordance with less extensive suberization due to reduced expression of suberin-related genes. The main entry sites of apoplasmically transported Cd were localized in the root apexes and lateral roots of the H ecotype, where suberin lamellae were not well developed. These findings highlight the significance of the apoplasmic bypass in Cd hyperaccumulation in hyperaccumulating ecotypes of S. alfredii.

• Keywords
• Apoplasmic bypass, cadmium, hydraulic conductance, lateral roots, root apex, Sedum alfredii, suberin lamellae, trisodium-8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS),
• MeSH
• Ecotype MeSH
• Gene Expression MeSH
• Cadmium metabolism   MeSH
• Plant Roots metabolism   MeSH
• Lipids genetics   physiology   MeSH
• Sedum genetics   metabolism   MeSH
• Xylem metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cadmium MeSH
• Lipids MeSH
• suberin MeSH Browser

Natural cytokinins as well as the majority of their synthetic derivatives show negative effects on root growth and development. Changes in morphology, primarily linked to the inhibition of the cell division in the meristematic zone, are manifested as thickening and shortening of the primary root and impaired lateral root branching. Rational design of cytokinin derivatives can partially overcome these drawbacks and reduce the negative effects. Using our database of cytokinin derivatives, we selected several aromatic cytokinin analogs with modifications at the N9 atom of the adenine moiety. We found that tetrahydropyranyl and tetrahydrofuranyl substitutions at the N9 atom led to enhanced acropetal transport of the modified cytokinin, and both derivatives also showed weak anticytokinin activity. Consequently, changes in the distribution of the active cytokinin pool together with gradual metabolic conversion of the modified cytokinin to its free form prevent root growth inhibition that limits cytokinin utilization in micropropagation techniques.

• Keywords
• N9-substituted cytokinins, biotechnology, cytokinin, inhibition, micropropagation, root, tissue culture,
• MeSH
• Cytokinins chemistry   pharmacology   MeSH
• Plant Roots drug effects   MeSH
• Zea mays MeSH
• Culture Techniques * MeSH
• Plant Development drug effects   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cytokinins MeSH

Strigolactones are the most recently recognized class of phytohormones, which are also known to establish plant symbiosis with arbuscular mycorhizal fungi or induce germination of parasitic plants. Their relatively complex structures and low stability urgently calls for simple derivatives with maintained biological function. We have prepared a series of triazolide strigolactone mimics and studied their ability to affect root development of Arabidopsis thaliana. The strigolactone mimics significantly induced root elongation and lateral root formation while resembling the effect of the reference compound GR24.

• MeSH
• Arabidopsis chemistry   drug effects   MeSH
• Germination drug effects   MeSH
• Plant Roots chemistry   drug effects   growth & development   MeSH
• Lactones chemistry   pharmacology   MeSH
• Molecular Structure MeSH
• Plant Growth Regulators chemistry   pharmacology   physiology   MeSH
• Symbiosis drug effects   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• GR24 compound MeSH Browser
• Lactones MeSH
• Plant Growth Regulators MeSH
• triazolide strigolactone MeSH Browser

Microcystin-LR (MCY-LR) is a heptapeptide toxin produced mainly by freshwater cyanobacteria. It strongly inhibits protein phosphatases PP2A and PP1. Functioning of the PIN family of auxin efflux carriers is crucial for plant ontogenesis and their functions depend on their reversible phosphorylation. We aimed to reveal the adverse effects of MCY-LR on PIN and auxin distribution in Arabidopsis roots and its consequences for root development. Relatively short-term (24 h) MCY-LR treatments decreased the levels of PIN1, PIN2 and PIN7, but not of PIN3 in tips of primary roots. In contrast, levels of PIN1 and PIN2 increased in emergent lateral roots and their levels depended on the type of PIN in lateral root primordia. DR5:GFP reporter activity showed that the cyanotoxin-induced decrease of auxin levels/responses in tips of main roots in parallel to PIN levels. Those alterations did not affect gravitropic response of roots. However, MCY-LR complemented the altered gravitropic response of crk5-1 mutants, defective in a protein kinase with essential role in the correct membrane localization of PIN2. For MCY-LR treated Col-0 plants, the number of lateral root primordia but not of emergent laterals increased and lateral root primordia showed early development. In conclusion, inhibition of protein phosphatase activities changed PIN and auxin levels, thus altered root development. Previous data on aquatic plants naturally co-occurring with the cyanotoxin showed similar alterations of root development. Thus, our results on the model plant Arabidopsis give a mechanistic explanation of MCY-LR phytotoxicity in aquatic ecosystems.

• Keywords
• Arabidopsis, Auxin, Microcystin-LR, PIN efflux Carrier, Protein phosphatase PP2A, Root development,
• MeSH
• Arabidopsis * genetics   MeSH
• Bacterial Toxins MeSH
• Ecosystem MeSH
• Plant Roots MeSH
• Indoleacetic Acids MeSH
• Microcystins MeSH
• Marine Toxins MeSH
• Protein Serine-Threonine Kinases MeSH
• Arabidopsis Proteins * genetics   MeSH
• Receptors, Cell Surface MeSH
• Cyanobacteria Toxins MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Bacterial Toxins MeSH
• CRK5 protein, Arabidopsis MeSH Browser
• cyanoginosin LR MeSH Browser
• Indoleacetic Acids MeSH
• Microcystins MeSH
• Marine Toxins MeSH
• Protein Serine-Threonine Kinases MeSH
• Arabidopsis Proteins * MeSH
• Receptors, Cell Surface MeSH
• Cyanobacteria Toxins MeSH

The At-Hook Motif Nuclear Localized Protein (AHL) gene family encodes embryophyte-specific nuclear proteins with DNA binding activity. They modulate gene expression and affect various developmental processes in plants. We identify AHL18 (At3G60870) as a developmental modulator of root system architecture and growth. AHL18 is involved in regulation of the length of the proliferation domain and number of dividing cells in the root apical meristem and thereby, cell production. Both primary root growth and lateral root development respond according to AHL18 transcription level. The ahl18 knock-out plants show reduced root systems due to a shorter primary root and a lower number of lateral roots. This change results from a higher number of arrested and non-developing lateral root primordia (LRP) rather than from a decreased LRP initiation. The over-expression of AHL18 results in a more extensive root system, longer primary roots, and increased density of lateral root initiation events. AHL18 is thus involved in the formation of lateral roots at both LRP initiation and their later development. We conclude that AHL18 participates in modulation of root system architecture through regulation of root apical meristem activity, lateral root initiation and emergence; these correspond well with expression pattern of AHL18.

• Keywords
• AHL18, AT-hook motif nuclear protein 18, Arabidopsis, At3G60870, Cell proliferation, Lateral root development, Root apical meristem,
• MeSH
• Arabidopsis genetics   growth & development   metabolism   MeSH
• AT-Hook Motifs MeSH
• DNA-Binding Proteins chemistry   genetics   metabolism   MeSH
• Plant Roots genetics   growth & development   metabolism   MeSH
• Mutation MeSH
• Arabidopsis Proteins chemistry   genetics   metabolism   MeSH
• Gene Expression Regulation, Plant MeSH
• Gene Expression Regulation, Developmental MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• DNA-Binding Proteins MeSH
• Arabidopsis Proteins MeSH

The development of above-ground lateral organs is initiated at the peripheral zone of the shoot apical meristem (SAM). The coordination of cell fate determination and the maintenance of stem cells are achieved through a complex regulatory network comprised of transcription factors. Two AP2/ERF transcription factor family genes, ESR1/DRN and ESR2/DRNL/SOB/BOL, regulate cotyledon and flower formation and de novo organogenesis in tissue culture. However, their roles in post-embryonic lateral organ development remain elusive. In this study, we analyzed the genetic interactions among SAM-related genes, WUS and STM, two ESR genes, and one of the HD-ZIP III members, REV, whose protein product interacts with ESR1 in planta. We found that esr1 mutations substantially enhanced the wus and stm phenotypes, which bear a striking resemblance to those of the wus rev and stm rev double mutants, respectively. Aberrant adaxial-abaxial polarity is observed in wus esr1 at relatively low penetrance. On the contrary, the esr2 mutation partially suppressed stm phenotypes in the later vegetative phase. Such complex genetic interactions appear to be attributed to the distinct expression pattern of two ESR genes because the ESR1 promoter-driving ESR2 is capable of rescuing phenotypes caused by the esr1 mutation. Our results pose the unique genetic relevance of ESR1 and the SAM-related gene interactions in the development of rosette leaves.

• Keywords
• Arabidopsis thaliana, ENHANCER OF SHOOT REGENERATION 1, REVOLTA, SHOOTMERISTEMLESS, WUSCHEL, adaxial–abaxial polarity, lateral organ, shoot apical meristem,
• MeSH
• Arabidopsis genetics   growth & development   MeSH
• Phenotype MeSH
• Homeodomain Proteins genetics   MeSH
• Plant Leaves genetics   growth & development   MeSH
• Meristem genetics   growth & development   MeSH
• Mutation MeSH
• Organogenesis, Plant genetics   MeSH
• Arabidopsis Proteins genetics   MeSH
• Gene Expression Regulation, Plant * MeSH
• Genes, Plant * MeSH
• Transcription Factors genetics   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• ESR1 protein, Arabidopsis MeSH Browser
• Homeodomain Proteins MeSH
• Arabidopsis Proteins MeSH
• Transcription Factors MeSH
• WUSCHEL protein, Arabidopsis MeSH Browser

Programmed cell death in plants occurs both during stress responses and as an integral part of regular plant development. Despite the undisputed importance of developmentally controlled cell death processes for plant growth and reproduction, we are only beginning to understand the underlying molecular genetic regulation. Exploiting the Arabidopsis thaliana root cap as a cell death model system, we identified two NAC transcription factors, the little-characterized ANAC087 and the leaf-senescence regulator ANAC046, as being sufficient to activate the expression of cell death-associated genes and to induce ectopic programmed cell death. In the root cap, these transcription factors are involved in the regulation of distinct aspects of programmed cell death. ANAC087 orchestrates postmortem chromatin degradation in the lateral root cap via the nuclease BFN1. In addition, both ANAC087 and ANAC046 redundantly control the onset of cell death execution in the columella root cap during and after its shedding from the root tip. Besides identifying two regulators of developmental programmed cell death, our analyses reveal the existence of an actively controlled cell death program in Arabidopsis columella root cap cells.

• MeSH
• Arabidopsis genetics   metabolism   MeSH
• Plant Roots genetics   metabolism   MeSH
• Meristem genetics   metabolism   MeSH
• Arabidopsis Proteins genetics   metabolism   MeSH
• Gene Expression Regulation, Plant MeSH
• Transcription Factors genetics   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Arabidopsis Proteins MeSH
• Transcription Factors MeSH