The Activity of a Tobacco Basic Chitinase Promotor in Transgenic White Clover Provides Insights into Plant Development and Symbiosis

1997 ◽  
Vol 24 (5) ◽  
pp. 555 ◽  
Author(s):  
Christopher Pittock ◽  
Jeremy J. Weinman ◽  
Barry G. Rolfe
Keyword(s):  
White Clover ◽  
Lateral Root ◽  
Transgene Expression ◽  
Lateral Roots ◽  
Developmental Expression ◽  
Nodule Formation ◽  
Post Inoculation ◽  
Environmental Response ◽  
Root Epidermis ◽  
Root Meristems

White clover was transformed with a tobacco basic chitinase promoter:GUS fusion. Basic chitinase promoter activity was detected by histochemical staining. Comparison of the spatial and temporal expression of the chitinase promoter-driven GUS gene in tobacco to that in white clover indicates that transcription from the promoter is induced by similar developmental and environmental response programs in each species. Wound-responsiveness of the white clover transgene was rapid and localised following mechanical and aphid (Family Aphididae) wounding. Developmental expression of the transgene during root morphogenesis reveals strong expression in tap and lateral root meristems but expression in lateral root meristems was observed only after the emergence through the tap root epidermis. No expression of the transgene was detected in the pericycle or the dividing cells of the developing lateral root. The expression of the tobacco basic chitinase promoter:GUS transgene in white clover was then used as a marker to examine the differences between the early developmental pathways leading to lateral root formation and those involoved in nodule formation in response to Rhizobium inoculation. Inoculation of the zone of emerging root hairs with a nodulation-competent Rhizobium strain ANU845(pRI4003), triggered transient transgene expression 2 to 4 h post-inoculation. No transgene expression was detectable after inoculation with purified Nod factor from strain ANU843. Our results suggest that lateral roots and nodules differ both in some of the mechanisms required to initiate cell division, and in their ongoing development after the emergence from the root epidermis.

Formation of lateral root meristems is a two-stage process

Development ◽  
1995 ◽  
Vol 121 (10) ◽  
pp. 3303-3310 ◽  
Author(s):  
M.J. Laskowski ◽  
M.E. Williams ◽  
H.C. Nusbaum ◽  
I.M. Sussex
Keyword(s):  
Lateral Root ◽  
Lateral Roots ◽  
Initial Period ◽  
Subsequent Stage ◽  
Root Initiation ◽  
Root Meristems ◽  
Lateral Root Initiation ◽  
Cell Layers ◽  
Stage Process ◽  
Pericycle Cells

In both radish and Arabidopsis, lateral root initiation involves a series of rapid divisions in pericycle cells located on the xylem radius of the root. In Arabidopsis, the number of pericycle cells that divide to form a primordium was estimated to be about 11. To determine the stage at which primordia are able to function as root meristems, primordia of different stages were excised and cultured without added hormones. Under these conditions, primordia that consist of 2 cell layers fail to develop while primordia that consist of at least 3–5 cell layers develop as lateral roots. We hypothesize that meristem formation is a two-step process involving an initial period during which a population of rapidly dividing, approximately isodiametric cells that constitutes the primordium is formed, and a subsequent stage during which meristem organization takes place within the primordium.

scholarly journals Potentiation of Lateral Root Induction by Root Initials in Isolated Flax Roots

1959 ◽  
Vol 12 (4) ◽  
pp. 388 ◽  
Author(s):  
PL Goldacre
Keyword(s):  
Cell Division ◽  
Lateral Root ◽  
Lateral Roots ◽  
Chemical Stimulus ◽  
Root Induction ◽  
Indolylacetic Acid ◽  
Root Meristems

When ,B-indolylacetic acid (IAA) (10-5M) is added to isolated flax roots, lateral roots are induced to form adventitiously. If some lateral root initials are already present when IAA is added, newly induced primordia form preferentially immediately adjacent to them. It is suggested that a chemical stimulus, a kinin, originating from the existing root meristems interacts with IAA to induce further cell division in the pericycle. It is proposed that kinin formation may be a normal accompaniment of cell division.

scholarly journals Natural variation identifies a Pxy gene controlling root vascular organization and formation of nodules and lateral roots in Lotus japonicus

2020 ◽  
Author(s):  
Yasuyuki Kawaharada ◽  
Niels Sandal ◽  
Vikas Gupta ◽  
Haojie Jin ◽  
Maya Kawaharada ◽  
...  
Keyword(s):  
Lateral Root ◽  
Reverse Genetics ◽  
De Novo ◽  
Lateral Roots ◽  
Lotus Japonicus ◽  
Nodule Formation ◽  
Mesorhizobium Loti ◽  
Genetic Overlap ◽  
Natural Variants ◽  
Trait Locus

AbstractForward and reverse genetics using the model legumes Lotus japonicus and Medicago truncatula have been instrumental for identifying the essential genes governing legume-rhizobial symbiosis. However, little is known about the effects of intraspecific variation on symbiotic signaling. The Lotus accessions Gifu and MG20 show differentiated phenotypic responses to the Mesorhizobium loti exoU mutant that produces truncated exopolysaccharides. Using Quantitative Trait Locus sequencing (QTL-seq), we identify the Pxy gene as a component of this differential exoU response. Lotus Pxy encodes a leucine-rich-repeat kinase similar to Arabidopsis PXY, which regulates stem vascular development. We show that Lotus pxy insertion mutants display defects in root vascular organization, as well as lateral root and nodule formation. Our work links Pxy to de novo organogenesis in the root, highlights the genetic overlap between regulation of lateral root and nodule formation, and demonstrates that specific natural variants of Pxy differentially affect nodulation signaling.

scholarly journals Auxin: at the root of nodule development?

2008 ◽  
Vol 35 (8) ◽  
pp. 651 ◽  
Author(s):  
Ulrike Mathesius
Keyword(s):  
Lateral Root ◽  
De Novo ◽  
Root Nodules ◽  
Lateral Roots ◽  
Nodule Development ◽  
Nodule Formation ◽  
Cortical Cells ◽  
Lateral Root Development ◽  
Organ Differentiation ◽  
Development And Differentiation

Root nodules are formed as a result of an orchestrated exchange of chemical signals between symbiotic nitrogen fixing bacteria and certain plants. In plants that form nodules in symbiosis with actinorhizal bacteria, nodules are derived from lateral roots. In most legumes, nodules are formed de novo from pericycle and cortical cells that are re-stimulated for division and differentiation by rhizobia. The ability of plants to nodulate has only evolved recently and it has, therefore, been suggested that nodule development is likely to have co-opted existing mechanisms for development and differentiation from lateral root formation. Auxin is an important regulator of cell division and differentiation, and changes in auxin accumulation and transport are essential for lateral root development. There is growing evidence that rhizobia alter the root auxin balance as a prerequisite for nodule formation, and that nodule numbers are regulated by shoot-to-root auxin transport. Whereas auxin requirements appear to be similar for lateral root and nodule primordium activation and organ differentiation, the major difference between the two developmental programs lies in the specification of founder cells. It is suggested that differing ratios of auxin and cytokinin are likely to specify the precursors of the different root organs.

Prenodule formation and primary nodule development in roots of Comptonia (Myricaceae)

1977 ◽  
Vol 55 (17) ◽  
pp. 2306-2318 ◽  
Author(s):  
Dale Callaham ◽  
John G. Torrey
Keyword(s):  
Root Hair ◽  
Lateral Root ◽  
Lateral Roots ◽  
Cortical Cell ◽  
Host Cells ◽  
Nodule Development ◽  
Nodule Formation ◽  
Cortical Cells ◽  
Lateral Root Primordium ◽  
Root Primordium

Seedlings of the sweet fern, Comptonia peregrina (L.) Coult., grown aeroponically, were inoculated with a nodule suspension to allow infection by the actinomycete-like organism which causes nodule formation. Roots with early stages of infection and nodule initiation were fixed, embedded in resin, sectioned, and examined. Infection is infrequent in Comptonia with only a few nodules per seedling root system. Infection via root hair invasion causes the retention of the curled and deformed root hair in an intensely cytoplasmic state with ramification of multiple filamentous strands of the endophyte. A limited cortical proliferation occurs in response to the infection forming the prenodule; endophyte filaments grow radially inward from the base of the infected epidermal root hair and invade a portion of the prenodular cells resulting in their hypertrophy. Distal and proximal to the prenodule site, a number of primary nodule primordia are initiated, varying from a few up to a dozen or more. These primordia appear to develop more or less simultaneously under the stimulus of the invading endophyte; they are like lateral roots in their site of origin, occurring largely opposite the protoxylem poles and involving pericyclic and endodermal cell proliferation. They differ in that the cortical cells external to each primordium are stimulated to undergo divisions and these cortical cell derivatives are incorporated into the developing primordium. The endophyte enters the cortical tissues of the lateral root on which the prenodule has formed and then invades proximal and distal to the infection site, progressing into the cortical tissues of each of the developing nodule primordia. A cork-like layer develops on the original lateral root in areas not occupied by primordia by initiation of subepidermal cell divisions and wall thickening. Normal lateral root primordium formation occurs in the pericycle opposite the protoxylem poles and involves cellular derivatives of the pericycle and endodermis but no cortical cells, which instead are crushed and displaced by the lateral root primordium as it develops. Nodule formation clearly involves complex chemical interactions, which remain for further study, between the host cells and the invading endophyte.

scholarly journals Auxin Response Factor 2 (ARF2), ARF3, and ARF4 Mediate Both Lateral Root and Nitrogen Fixing Nodule Development in Medicago truncatula

2021 ◽  
Vol 12 ◽  
Author(s):  
Cristina Kirolinko ◽  
Karen Hobecker ◽  
Jiangqi Wen ◽  
Kirankumar S. Mysore ◽  
Andreas Niebel ◽  
...  
Keyword(s):  
Medicago Truncatula ◽  
Root Development ◽  
Lateral Root ◽  
Lateral Roots ◽  
Nodule Development ◽  
Nodule Formation ◽  
Mrna Levels ◽  
Nitrogen Fixing ◽  
Auxin Response ◽  
Small Interference Rna

Auxin Response Factors (ARFs) constitute a large family of transcription factors that mediate auxin-regulated developmental programs in plants. ARF2, ARF3, and ARF4 are post-transcriptionally regulated by the microRNA390 (miR390)/trans-acting small interference RNA 3 (TAS3) module through the action of TAS3-derived trans-acting small interfering RNAs (ta-siRNA). We have previously reported that constitutive activation of the miR390/TAS3 pathway promotes elongation of lateral roots but impairs nodule organogenesis and infection by rhizobia during the nitrogen-fixing symbiosis established between Medicago truncatula and its partner Sinorhizobium meliloti. However, the involvement of the targets of the miR390/TAS3 pathway, i.e., MtARF2, MtARF3, MtARF4a, and MtARF4b, in root development and establishment of the nitrogen-fixing symbiosis remained unexplored. Here, promoter:reporter fusions showed that expression of both MtARF3 and MtARF4a was associated with lateral root development; however, only the MtARF4a promoter was active in developing nodules. In addition, up-regulation of MtARF2, MtARF3, and MtARF4a/b in response to rhizobia depends on Nod Factor perception. We provide evidence that simultaneous knockdown of MtARF2, MtARF3, MtARF4a, and MtARF4b or mutation in MtARF4a impaired nodule formation, and reduced initiation and progression of infection events. Silencing of MtARF2, MtARF3, MtARF4a, and MtARF4b altered mRNA levels of the early nodulation gene nodulation signaling pathway 2 (MtNSP2). In addition, roots with reduced levels of MtARF2, MtARF3, MtARF4a, and MtARF4b, as well as arf4a mutant plants exhibited altered root architecture, causing a reduction in primary and lateral root length, but increasing lateral root density. Taken together, our results suggest that these ARF members are common key players of the morphogenetic programs that control root development and the formation of nitrogen-fixing nodules.

scholarly journals Flavonoids Synthesized in Cortical Cells During Nodule Initiation Are Early Developmental Markers in White Clover

1998 ◽  
Vol 11 (12) ◽  
pp. 1223-1232 ◽  
Author(s):  
Ulrike Mathesius ◽  
Cathy Bayliss ◽  
Jeremy J. Weinman ◽  
Helmi R. M. Schlaman ◽  
Herman P. Spaink ◽  
...  
Keyword(s):  
White Clover ◽  
Rhizobium Leguminosarum ◽  
Fluorescence Emission ◽  
Emission Spectra ◽  
Water Soluble ◽  
Nodule Formation ◽  
Post Inoculation ◽  
Flavonoid Pathway ◽  
Nodule Initiation ◽  
Inner Cortex

We examined the site-specific induction of the flavonoid pathway before and during nodule initiation in white clover with transgenic plants, fluorescence microscopy, and microspectrofluorometry to test if flavonoids play a role in nodule organogenesis. A chalcone synthase regulated β-glucuronidase (GUS) transgene (CHS3:gusA) was up-regulated from 3 h post inoculation (p.i.) until cell division (around 40 h p.i.) in inner cortex cells underlying the inoculation site. Intracellular fluorescence occurred in vacuoles of those inner cortex cells from 13 h p.i. until the fluorescent cells divided. Fluorescence emission spectra of contents of individual fluorescing cortex cells were measured in situ and compared with emission spectra of compounds purified from root extracts. The fluorescing compound located in cells of the inner cortex after Rhizobium leguminosarum bv. trifolii infection was identified as a water-soluble derivative of 7,4′-dihydroxyflavone. Nodule primordium cells contained a different fluorescent compound, identified as the isoflavonoid formononetin. CHS3:gusA expression and flavonoid accumulation were only induced in inner cortex cells by a nodulating Rhizo-bium strain and by clover-specific lipo-chitinoligosac-charides, but not by non-nodulating rhizobia. Fluorescence was also induced by compatible rhizobia in other legumes such as alfalfa, pea, and siratro in the cells that participate in nodule initiation. Our results show that fluorescent flavonoids are useful markers in nodule or-ganogenesis in clover and may have direct roles in nodule formation.

Lateral root formation and nutrients: nitrogen in the spotlight

2021 ◽  
Author(s):  
Pierre-Mathieu Pélissier ◽  
Hans Motte ◽  
Tom Beeckman
Keyword(s):  
Signaling Pathways ◽  
Root System ◽  
Root Development ◽  
Lateral Root ◽  
Molecular Mechanisms ◽  
Root Formation ◽  
Lateral Roots ◽  
Nutrient Use Efficiency ◽  
Lateral Root Formation ◽  
Lateral Root Development

Abstract Lateral roots are important to forage for nutrients due to their ability to increase the uptake area of a root system. Hence, it comes as no surprise that lateral root formation is affected by nutrients or nutrient starvation, and as such contributes to the root system plasticity. Understanding the molecular mechanisms regulating root adaptation dynamics towards nutrient availability is useful to optimize plant nutrient use efficiency. There is at present a profound, though still evolving, knowledge on lateral root pathways. Here, we aimed to review the intersection with nutrient signaling pathways to give an update on the regulation of lateral root development by nutrients, with a particular focus on nitrogen. Remarkably, it is for most nutrients not clear how lateral root formation is controlled. Only for nitrogen, one of the most dominant nutrients in the control of lateral root formation, the crosstalk with multiple key signals determining lateral root development is clearly shown. In this update, we first present a general overview of the current knowledge of how nutrients affect lateral root formation, followed by a deeper discussion on how nitrogen signaling pathways act on different lateral root-mediating mechanisms for which multiple recent studies yield insights.

Effects of a Nod-factor-overproducing strain of Sinorhizobium meliloti on the expression of the ENOD40 gene in Melilotus alba

2002 ◽  
Vol 80 (9) ◽  
pp. 907-915 ◽  
Author(s):  
Walter F Giordano ◽  
Michelle R Lum ◽  
Ann M Hirsch
Keyword(s):  
Lateral Root ◽  
Sinorhizobium Meliloti ◽  
Cortical Cell ◽  
Host Cells ◽  
Nodule Development ◽  
Nodule Formation ◽  
Additional Increase ◽  
Nod Factor ◽  
Melilotus Alba ◽  
Different Strains

We have initiated studies on the molecular biology and genetics of white sweetclover (Melilotus alba Desr.) and its responses to inoculation with the nitrogen-fixing symbiont Sinorhizobium meliloti. Early nodulin genes such as ENOD40 serve as markers for the transition from root to nodule development even before visible stages of nodule formation are evident. Using Northern blot analysis, we found that the ENOD40 gene was expressed within 6 h after inoculation with two different strains of S. meliloti, one of which overproduces symbiotic Nod factors. Inoculation with this strain resulted in an additional increase in ENOD40 gene expression over a typical wild-type S. meliloti strain. Moreover, the increase in mRNA brought about by the Nod-factor-overproducing strain 24 h after inoculation was correlated with lateral root formation by using whole-mount in situ hybridization to localize ENOD40 transcripts in lateral root meristems and by counting lateral root initiation sites. Cortical cell divisions were not detected. We also found that nodulation occurred more rapidly on white sweetclover in response to the Nod-factor-overproducing strain, but ultimately there was no difference in nodulation efficiency in terms of nodule number or the number of roots nodulated by the two strains. Also, the two strains could effectively co-colonize the host when inoculated together, although a few host cells were occupied by both strains.Key words: ENOD40, Nod factor, Melilotus, Sinorhizobium, symbiosis.

scholarly journals AT-HOOK MOTIF NUCLEAR LOCALISED PROTEIN 18 as a Novel Modulator of Root System Architecture

2020 ◽  
Author(s):  
Marek Šírl ◽  
Tereza Šnajdrová ◽  
Dolores Gutiérrez-Alanís ◽  
Joseph G. Dubrovsky ◽  
Jean Phillipe Vielle-Calzada ◽  
...  
Keyword(s):  
Root System ◽  
System Architecture ◽  
Lateral Root ◽  
Apical Meristem ◽  
Lateral Roots ◽  
Primary Root ◽  
Root System Architecture ◽  
Root Apical Meristem ◽  
Root Initiation ◽  
Lateral Root Initiation

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 regulates 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 decreased initiation. Overexpression of AHL18 results in a more extensive root system, longer primary roots, and increased density of lateral root initiation events. Formation of lateral roots is affected during the initiation of LRP and later development. AHL18 regulate root apical meristem activity, lateral root initiation and emergence, which is in accord with localization of its expression.

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