Adventitious Root Primordia Research Articles

Comparative RNA-seq based transcriptome profiling of waterlogging response in cucumber hypocotyls reveals novel insights into the de novo adventitious root primordia initiation

BackgroundWaterlogging is a serious abiotic stress to plant growth because it results in the decline in the supplement of oxygen to submerged tissues. Although cucumber (Cucumis sativus L.) is sensitive to waterlogging, its ability to generate adventitious roots (ARs) facilitates gas diffusion and increases plant survival when the oxygen concentration is decreased. To gain a better understanding of the molecular mechanisms that enable de novo AR primordia emergence upon waterlogging, the RNA sequencing-based transcriptomic responses of two contrasting cucumber genotypes, Zaoer-N (waterlogging tolerant) and Pepino (waterlogging sensitive), which differed in their abilities to form AR were compared.ResultsMore than 27,000 transcripts were detected in cucumber hypocotyls, from which 1494 and 1766 genes in ‘Zaoer-N’ and ‘Pepino’, respectively, were differentially expressed 2 days after waterlogging. The significant positive correlation between RNA sequencing data and a qPCR analysis indicated that the identified genes were credible. A comparative analysis revealed that genes functioning in carbohydrate mobilization, nitrate assimilation, hormone production and signaling pathways, transcription factors and cell division might contribute to the waterlogging-triggered AR primordia initiation. Ethylene was determined to be an important plant hormone responsible for the cucumber ARs initiation. Additionally, genes encoding cytochrome P450, ankyrin repeat-containing proteins and sulfite oxidases were determined as important in waterlogging acclimation.ConclusionThis research broadens our understanding of the mechanism underlying waterlogging-triggered ARs emergence, and provides valuable information for the breeding of cucumber with enhanced waterlogging tolerance.

A specific role of iron in promoting meristematic cell division during adventitious root formation.

Adventitious root (AR) formation is characterized by a sequence of physiological and morphological processes and determined by external factors, including mineral nutrition, the impacts of which remain largely elusive. Morphological and anatomical evaluation of the effects of mineral elements on AR formation in leafy cuttings of Petunia hybrida revealed a striking stimulation by iron (Fe) and a promotive action of ammonium (NH4+). The optimal application period for these nutrients corresponded to early division of meristematic cells in the rooting zone and coincided with increased transcript levels of mitotic cyclins. Fe-localization studies revealed an enhanced allocation of Fe to the nuclei of meristematic cells in AR initials. NH4+ supply promoted AR formation to a lesser extent, most likely by favoring the availability of Fe. We conclude that Fe acts locally by promoting cell division in the meristematic cells of AR primordia. These results highlight a specific biological function of Fe in AR development and point to an unexploited importance of Fe for the vegetative propagation of plants from cuttings.

Differential auxin transport and accumulation in the stem base lead to profuse adventitious root primordia formation in the aerial roots (aer) mutant of tomato (Solanum lycopersicum L.)

The aerial roots (aer) mutant of tomato is characterized by a profuse and precocious formation of adventitious root primordia along the stem. We demonstrated that auxin is involved in the aer phenotype but ruled out higher auxin sensitivity of mutant plants. Interestingly, polar auxin transport was altered in aer, as young seedlings showed a reduced response to an auxin transport inhibitor and higher expression of auxin export carriers SlPIN1 and SlPIN3. An abrupt reduction in transcripts of auxin efflux and influx genes in older aer hypocotyls caused a marked deceleration of auxin transport in more mature tissues. Indeed, in 20days old aer plants, the transport of labeled IAA was faster in apices than in hypocotyls, displaying an opposite trend in comparison to a wild type. In addition, auxin transport facilitators (SlPIN1, SlPIN4, SlLAX5) were more expressed in aer apices than in hypocotyls, suggesting that auxin moves faster from the upper to the lower part of the stem. Consequently, a significantly higher level of free and conjugated IAA was found at the base of aer stems with respect to their apices. This auxin accumulation is likely the cause of the aer phenotype.

Awaiting better times: A quiescence response and adventitious root primordia formation prolong survival under cadmium stress in Tetradenia riparia (Hochst.) Codd

Plants survive stressful conditions by employing three main strategies: escape, tolerance, and survival. Experiments were conducted to pinpoint the response strategy adopted by Tetradenia riparia to cadmium (Cd) stress by monitoring several physiological parameters and plants’ ability to recover once the stress receded. Cadmium (30 and 150μM) strongly affected shoot and root growth in a dose dependent manner, with almost complete inhibition of shoot growth, stomatal opening and CO2 assimilation in plants exposed to 150μM CdSO4. Independently of the CdSO4 concentrations, plants excluded Cd from the aboveground tissues, with concentrations in shoots remaining around 0.1μmolg−1 dry mass. Furthermore, Cd stress was associated with a decline in methylation of Lys4 of histone H3, likely associated with the transition from an active to a quiescent state. Surprisingly, Cd also induced the initiation of root primordia in T. riparia stems, which, once placed in a Cd-free media, quickly (24h) developed into adventitious roots, which were likely the driving factor of the rapid resumption of leaf elongation and photosynthetic activity, which increased almost 20-fold over the 3 weeks of recovery. Therefore T. riparia ability to survive Cd stress was mediated by quiescence, which associated with an excluder strategy and stem root primordia formation, enabled rapid resumption of growth under Cd-free conditions.

Rapid formation of adventitious roots and partial ethylene sensitivity result in faster adaptation to flooding in the aerial roots (aer) mutant of tomato

The frequency of extreme events such as droughts and floods has increased as a consequence of climate change. Many crops have not been improved to tolerate soil anoxia and, therefore, floods cause important economic losses. During submergence, Solanum lycopersicum L. exhibits three distinct responses which are adventitious root production, epinasty and aerenchyma formation. The development of a new adventitious root system is crucial as it can replace the original roots that succumb to the hypoxic environment. Aerial roots (aer) is a tomato mutant characterized by the presence of numerous adventitious root primordia along the hypocotyl and older internodes. In this work, we have analyzed the aer mutant behavior to flooding to determine whether preformed adventitious roots represent an adaptive advantage with respect to biomass accumulation. We have also examined other morphological and anatomical responses of aer plants to detect differential adaptations under flooding. Aer plants form an abundant adventitious root system faster than Ailsa Craig cultivar, which results in flooded plants accumulating as much biomass as non-flooded aer plants. In addition, several ethylene-induced responses such as epinasty, hypertrophy, aerenchyma production, and apical hook formation are reduced in aer, suggesting a lower sensitivity of some tissues to ethylene. The E4 expression level, an ethylene-induced gene, confirmed this observation since E4 transcripts are less abundant in petioles and stems of ethylene-treated aer plants, coinciding with the tissues that present a lower degree of morphological and/or anatomical response. Evidence from the Never ripe mutant suggests a reduction in ethylene sensitivity could contribute to the attenuation of flooding effects. Therefore, our results indicate that the rapid formation of a new root system together with a reduction in ethylene sensitivity is responsible of a faster adaptation to flooding stress in the aer mutant.

Chrysanthemum transcription factor CmLBD1 direct lateral root formation in Arabidopsis thaliana.

The plant-specific LATERAL ORGAN BOUNDARIES DOMAIN (LBD) genes are important regulators of growth and development. Here, a chrysanthemum class I LBD transcription factor gene, designated CmLBD1, was isolated and its function verified. CmLBD1 was transcribed in both the root and stem, but not in the leaf. The gene responded to auxin and was shown to participate in the process of adventitious root primordium formation. Its heterologous expression in Arabidopsis thaliana increased the number of lateral roots formed. When provided with exogenous auxin, lateral root emergence was promoted. CmLBD1 expression also favored callus formation from A. thaliana root explants in the absence of exogenously supplied phytohormones. In planta, CmLBD1 probably acts as a positive regulator of the response to auxin fluctuations and connects auxin signaling with lateral root formation.

Adventitious root primordia formation and development in stem nodes of 'Georgia Jet' sweetpotato, Ipomoea batatas.

• Yield in sweetpotato is determined by the number of storage roots produced per plant. Storage roots develop from adventitious roots (ARs) present in stem cuttings that serve as propagation material. Data on the origin of sweetpotato ARs and the effect of nodal position on AR establishment and further development are limited.• We anatomically described root primordium initiation using stem sections and measured number of root primordia formed at different nodal positions using light microscopy and correlated nodal positions with AR number and length 14 d after planting (DAP).• Primordia for ARs initiate at the junction of the stem pith ray and the cambium, on both sides of the leaf gap, and they are well developed before emerging from the stem. The number of ARs that develop from isolated stem nodes 14 DAP corresponded to the number of AR primordia detected inside the stem. The total length of established roots at nodes 9-13 from the apex is about 2-fold longer than at nodes 5-8.• Nodal position (age) has a significant effect on the developmental status and number of root primordia inside the stem, determining the number and length of ARs that have developed by 14 DAP. Adventitious roots originating from nodes 9-13 possess similar AR systems and develop better than those originating from younger nodes 3-8. The mechanism regulating AR initiation in nodes is discussed. This system can serve for studying the effect of environmental conditions on AR initiation, development, and capacity to form storage roots.

Life cycle stage and water depth affect flooding-induced adventitious root formation in the terrestrial species Solanum dulcamara.

Flooding can occur at any stage of the life cycle of a plant, but often adaptive responses of plants are only studied at a single developmental stage. It may be anticipated that juvenile plants may respond differently from mature plants, as the amount of stored resources may differ and morphological changes can be constrained. Moreover, different water depths may require different strategies to cope with the flooding stress, the expression of which may also depend on developmental stage. This study investigated whether flooding-induced adventitious root formation and plant growth were affected by flooding depth in Solanum dulcamara plants at different developmental stages. Juvenile plants without pre-formed adventitious root primordia and mature plants with primordia were subjected to shallow flooding or deep flooding for 5 weeks. Plant growth and the timing of adventitious root formation were monitored during the flooding treatments. Adventitious root formation in response to shallow flooding was significantly constrained in juvenile S. dulcamara plants compared with mature plants, and was delayed by deep flooding compared with shallow flooding. Complete submergence suppressed adventitious root formation until up to 2 weeks after shoots restored contact with the atmosphere. Independent of developmental stage, a strong positive correlation was found between adventitious root formation and total biomass accumulation during shallow flooding. The potential to deploy an escape strategy (i.e. adventitious root formation) may change throughout a plant's life cycle, and is largely dependent on flooding depth. Adaptive responses at a given stage of the life cycle thus do not necessarily predict how the plant responds to flooding in another growth stage. As variation in adventitious root formation also correlates with finally attained biomass, this variation may form the basis for variation in resistance to shallow flooding among plants.

Gene expression profiling in juvenile and mature cuttings of Eucalyptus grandis reveals the importance of microtubule remodeling during adventitious root formation.

BackgroundThe ability to form adventitious roots (AR) is an economically important trait that is lost during the juvenile-to-mature phase change in woody plants. Auxin treatment, which generally promotes rooting in juvenile cuttings, is often ineffective when applied to mature cuttings. The molecular basis for this phenomenon in Eucalyptus grandis was addressed here.ResultsA comprehensive microarray analysis was performed in order to compare gene-expression profiles in juvenile and mature cuttings of E. grandis, with or without auxin treatment on days, 0, 1, 3, 6, 9 and 12 post AR induction. Under these conditions AR primordia were formed only in auxin-treated juvenile cuttings. However, clustering the expression profiles revealed that the time after induction contributed more significantly to the differences in expression than the developmental phase of the cuttings or auxin treatment. Most detected differences which were related to the developmental phase and auxin treatment occurred on day 6, which correlated with the kinetics of AR-primordia formation. Among the functional groups of transcripts that differed between juvenile and mature cuttings was that of microtubules (MT). The expression of 42 transcripts annotated as coding for tubulin, MT-associated proteins and kinesin motor proteins was validated in the same RNA samples. The results suggest a coordinated developmental and auxin dependent regulation of several MT-related transcripts in these cuttings. To determine the relevance of MT remodeling to AR formation, MTs were subjected to subtle perturbations by trifluralin, a MT disrupting drug, applied during auxin induction. Juvenile cuttings were not affected by the treatment, but rooting of mature cuttings increased from 10 to more than 40 percent.ConclusionsThe data suggest that juvenile-specific MT remodeling is involved in AR formation in E. grandis.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-826) contains supplementary material, which is available to authorized users.

Morpho-anatomic of adventitious rhizogenesis in mini-cuttings of Eucalyptus grandis x Eucalyptus urophylla

The present work aimed to accomplish the histological analysis of the events involved in the adventitious rooting pattern of four Eucalyptus grandis x Eucalyptus urophylla clones. The mini-cuttings were collected from a mini-stump and the rooting experiments were set up under mini-hedge indoor semi-hydroponics by means of intermittent flooding fertirrigation. For histological analyses, the proximal ends of the mini-cuttings were collected after 0, 1, 2, 4, 6, 8, 10, and 12 days after planting them at greenhouse. After fixation with FAA70%, the samples were dehydrated in a graded ethanol series and infiltrated overnight in metracrilate resin, and finally embedded in resin. It was verified the endogenous origin of adventitious root primordia from vascular cambium, and in some cases, the formation and proliferation of calli at the proximal end of the mini-cuttings within 8 to 12 days.

1-Methylcyclopropene Has a Variable Effect on Adventitious Root Emergence from Cuttings of Two Sweetpotato Cultivars

This study aimed to investigate the effect of 1-methylcyclopropene (1-MCP) on adventitious rooting in two sweetpotato cultivars. Experiments with ‘Beauregard’ and ‘Evangeline’ sweetpotato cuttings revealed differential adventitious root (AR) emergence responses to 1-MCP application. ‘Beauregard’ AR count and length decreased with 1-MCP application in two of four experiments. In contrast, 1-MCP did not influence ‘Evangeline’ root count. However, ‘Evangeline’ root length decreased in three of four experiments. Trypan blue staining of ‘Beauregard’ nodal tissue with delayed AR primordia emergence showed localized dead tissue in the general area where ARs emerge. The degree of staining appeared to correspond with the stage of AR emergence with the staining becoming more intense around the time an AR primordium eventually emerged through a crack in the epidermis. This response agrees with reported results of ethylene-mediated AR emergence in other plant species. These results also appear to suggest that ‘Beauregard’ and ‘Evangeline’ cuttings differ in ethylene sensitivity. This represents the first evidence of genotype-specific ethylene involvement in adventitious rooting of sweetpotato cuttings.

Emerging Roots Alter Epidermal Cell Fate through Mechanical and Reactive Oxygen Species Signaling

A central question in biology is how spatial information is conveyed to locally establish a developmental program. Rice (Oryza sativa) can survive flash floods by the emergence of adventitious roots from the stem. Epidermal cells that overlie adventitious root primordia undergo cell death to facilitate root emergence. Root growth and epidermal cell death are both controlled by ethylene. This study aimed to identify the signal responsible for the spatial control of cell death. Epidermal cell death correlated with the proximity to root primordia in wild-type and ADVENTITIOUS ROOTLESS1 plants, indicating that the root emits a spatial signal. Ethylene-induced root growth generated a mechanical force of ~18 millinewtons within 1 h. Force application to epidermal cells above root primordia caused cell death in a dose-dependent manner and was inhibited by 1-methylcyclopropene or diphenylene iodonium, an inhibitor of NADPH oxidase. Exposure of epidermal cells not overlying a root to either force and ethylene or force and the catalase inhibitor aminotriazole induced ectopic cell death. Genetic downregulation of the reactive oxygen species (ROS) scavenger METALLOTHIONEIN2b likewise promoted force-induced ectopic cell death. Hence, reprogramming of epidermal cell fate by the volatile plant hormone ethylene requires two signals: mechanosensing for spatial resolution and ROS for cell death signaling.

Strigolactones suppress adventitious rooting in Arabidopsis and pea.

Adventitious root formation is essential for the propagation of many commercially important plant species and involves the formation of roots from nonroot tissues such as stems or leaves. Here, we demonstrate that the plant hormone strigolactone suppresses adventitious root formation in Arabidopsis (Arabidopsis thaliana) and pea (Pisum sativum). Strigolactone-deficient and response mutants of both species have enhanced adventitious rooting. CYCLIN B1 expression, an early marker for the initiation of adventitious root primordia in Arabidopsis, is enhanced in more axillary growth2 (max2), a strigolactone response mutant, suggesting that strigolactones restrain the number of adventitious roots by inhibiting the very first formative divisions of the founder cells. Strigolactones and cytokinins appear to act independently to suppress adventitious rooting, as cytokinin mutants are strigolactone responsive and strigolactone mutants are cytokinin responsive. In contrast, the interaction between the strigolactone and auxin signaling pathways in regulating adventitious rooting appears to be more complex. Strigolactone can at least partially revert the stimulatory effect of auxin on adventitious rooting, and auxin can further increase the number of adventitious roots in max mutants. We present a model depicting the interaction of strigolactones, cytokinins, and auxin in regulating adventitious root formation.

The influence of adenine and benzyladenine on rooting and development of Fuchsia hybrida cuttings

Cytokinins are a group of plant hormones stimulating, among others, axillary bud formation and inhibiting rhizogenesis. Adenine, their common component, often expresses cytokinin-like activity in plant development. The aim of the experiment was to determine the effect of adenine on rooting and development of <em>Fuchsia hybrida </em>cuttings. The influence of adenine was also assessed in comparison to benzyladenine, including their cooperation with 1-naphthaleneacetic acid. Anatomical analysis of the rooting process was also undertaken. Application of BA, both alone or together with NAA, strongly inhibited rhizogenesis, but stimulated axillary shoot outgrowth. Adenine exhibited cytokinin-like activity on axillary shoot development in <em>Fuchsia hybrida </em>cuttings, but did not show the inhibitory effect on root development typical for cytokinins. This compound, particularly at higher concentrations, stimulated both axillary shoot development and rooting, which was expressed as an increase in root number and rooting percentage, even after direct application to the base of the cuttings. Anatomical analysis revealed adenine-derived acceleration during elongation of adventitious root primordia.

Identification of pectin methylesterase 3 as a basic pectin methylesterase isoform involved in adventitious rooting in Arabidopsis thaliana

• Here, we focused on the biochemical characterization of the Arabidopsis thaliana pectin methylesterase 3 gene (AtPME3; At3g14310) and its role in plant development. • A combination of biochemical, gene expression, Fourier transform-infrared (FT-IR) microspectroscopy and reverse genetics approaches were used. • We showed that AtPME3 is ubiquitously expressed in A. thaliana, particularly in vascular tissues. In cell wall-enriched fractions, only the mature part of the protein was identified, suggesting that it is processed before targeting the cell wall. In all the organs tested, PME activity was reduced in the atpme3-1 mutant compared with the wild type. This was related to the disappearance of an activity band corresponding to a pI of 9.6 revealed by a zymogram. Analysis of the cell wall composition showed that the degree of methylesterification (DM) of galacturonic acids was affected in the atpme3-1 mutant. A change in the number of adventitious roots was found in the mutant, which correlated with the expression of the gene in adventitious root primordia. • Our results enable the characterization of AtPME3 as a major basic PME isoform in A. thaliana and highlight its role in adventitious rooting.

A Dominant Mutation in ARL2 Causes Impaired Adventitious Root Development in Rice

Adventitious roots are vital for water and nutrient assimilation by cereal crops because they comprise the bulk of the fibrous root system. We isolated and analyzed a rice mutant, adventitious rootless 2 (arl2), which failed to initiate adventitious root primordia during early development. Its seminal root produced fewer lateral roots than from the wild type. This mutant also exhibited pleiotropic phenotypes of longer and thicker seminal roots, a different morphology for the first leaf, delayed heading, and a greater tiller angle. Physiological experiments showed that exogenous auxin and ethylene could rescue adventitious root growth, a response opposite that for two previously reported mutants, arl1 and gnom1. Activity in the auxin signal pathway and the polar auxin transport system was normal for arl2. Compared with the wild type, arl2 plants showed enhanced sensitivity to ethephon but decreased sensitivity to AgNO3, an inhibitor of ethylene. Genetics analysis demonstrated that this mutant is controlled by a single dominant gene; ARL2 was mapped within a 100-kb interval on the short arm of chromosome 2.

Can Changes in Starch Content and Peroxidase Activity Be Used as Rooting Phase Markers for Rhododendron Leaf Bud Cuttings?

We examined whether peroxidase activity in cutting bases and leaves and starch content in cutting bases can be used as rooting phase markers in the elepidote rhododendron cv. 'Babites Baltais' (Rhododendron L.). Changes in peroxidase activity in cutting leaves and bases, as well as starch content in cutting bases, were determined in relation to anatomical stages of rhizogenesis in leaf bud cuttings treated with 1% indole-3-butyric acid (IBA+) or without IBA (IBA–). The pattern of change of peroxidase activity was similar in cutting bases and leaves of IBAleaf bud cuttings. Three phases of adventitious root formation were identified: induction, initiation and expression. During the induction phase peroxidase activity decreased, but no anatomical changes were observed in the cuttings. Peroxidase activity increased in the initiation phase when adventitious root initials were formed. Peroxidase activity decreased during the expression phase when adventitious root primordia developed. The starch content of IBA– leaf bud cuttings decreased during the first few days and then gradually rose to maximum, followed by a sharp reduction and another increase at the end of the experiment. The changes of starch content did not coincide with rooting phases as peroxidase activity did, and cannot be used as a rooting phase marker in rhododendrons. Adventitious root formation did not occur in IBA+ leaf bud cuttings, so distinct rooting phases could not be observed. There was a significant correlation between peroxidase activity in cutting bases and leaves of IBA- leaf bud cuttings. Peroxidase activity in leaves of rhododendron leaf bud cuttings are potentially useful as a marker for rooting phases, but that requires further anatomical and physiological study of rooting in leaf bud cuttings.

Anatomical study on rooting of Lonicera macranthoides cutting

An anatomical study on rooting of Lonicera macranthoides cutting was carried out by the paraffin section method. The observation result showed that there was no root primordium in stem, and the adventitious root primordium of L. macranthoides cutting belonged to the type of the induced root primordium. The adventitious root primordium originated from the cross region of vascular cambium and pith rays. There was no root primordium in the wound calls, between them it existed no direct relationship.

Heterotrimeric G Protein Signaling Is Required for Epidermal Cell Death in Rice

In rice (Oryza sativa) adventitious root primordia are formed at the nodes as part of normal development. Upon submergence of rice plants, adventitious roots emerge from the nodes preceded by death of epidermal cells above the root primordia. Cell death is induced by ethylene and mediated by hydrogen peroxide (H(2)O(2)). Pharmacological experiments indicated that epidermal cell death was dependent on signaling through G proteins. Treatment with GTP-gamma-S induced epidermal cell death, whereas GDP-beta-S partially inhibited ethylene-induced cell death. The dwarf1 (d1) mutant of rice has repressed expression of the Galpha subunit RGA1 of heterotrimeric G protein. In d1 plants, cell death in response to ethylene and H(2)O(2) was nearly completely abolished, indicating that signaling through Galpha is essential. Ethylene and H(2)O(2) were previously shown to alter gene expression in epidermal cells that undergo cell death. Transcriptional regulation was not generally affected in the d1 mutant, indicating that altered gene expression is not sufficient to trigger cell death in the absence of Galpha. Analysis of genes encoding proteins related to G protein signaling revealed that four small GTPase genes, two GTPase-activating protein genes, and one GDP dissociation inhibitor gene but not RGA1 were differentially expressed in epidermal cells above adventitious roots, indicating that Galpha activity is regulated posttranscriptionally.

Adventitious root formation in rice requires OsGNOM1 and is mediated by the OsPINs family

The fibrous root system in cereals comprises primarily adventitious roots (ARs), which play important roles in nutrient and water uptake. Current knowledge regarding the molecular mechanism underlying AR development is still limited. We report here the isolation of four rice (Oryza sativa L.) mutants, from different genetic backgrounds, all of which were defective in AR formation. These mutants exhibited reduced numbers of lateral roots (LRs) and partial loss of gravitropism. The mutants also displayed enhanced sensitivity to N-1-naphthylphthalamic acid, an inhibitor of polar auxin transport (PAT), indicating that the mutations affected auxin transport. Positional cloning using one of the four mutants revealed that it was caused by loss-of-function of a guanine nucleotide exchange factor for ADP-ribosylation factor (OsGNOM1). RT-PCR and analysis of promoter::GUS transgenic plants showed that OsGNOM1 is expressed in AR primordia, vascular tissues, LRs, root tips, leaves, anthers and lemma veins, with a distribution pattern similar to that of auxin. In addition, the expressions of OsPIN2, OsPIN5b and OsPIN9 were altered in the mutants. Taken together, these findings indicate that OsGNOM1 affects the formation of ARs through regulating PAT.