MtNRLK1, a CLAVATA1-like leucine-rich repeat receptor-like kinase upregulated during nodulation in Medicago truncatula.

Peptides are signaling molecules regulating various aspects of plant development, including the balance between cell division and differentiation in different meristems. Among those, CLAVATA3/Embryo Surrounding Region-related (CLE-ESR) peptide activity depends on leucine-rich-repeat receptor-like-kinases (LRR-RLK) belonging to the subclass XI. In legume plants, such as the Medicago truncatula model, specific CLE peptides were shown to regulate root symbiotic nodulation depending on the LRR-RLK SUNN (Super Numeric Nodules).

Role of LONELY GUY genes in indeterminate nodulation on Medicago truncatula.

LONELY GUY (LOG) genes encode cytokinin riboside 5'-monophosphate phosphoribohydrolases and are directly involved in the activation of cytokinins. To assess whether LOG proteins affect the influence of cytokinin on nodulation, we studied two LOG genes of Medicago truncatula. Expression analysis showed that MtLOG1 and MtLOG2 were upregulated during nodulation in a CRE1-dependent manner.

pFiD188, the linear virulence plasmid of Rhodococcus fascians D188.

Rhodococcus fascians is currently the only phytopathogen of which the virulence genes occur on a linear plasmid. To get insight into the origin of this replicon and into the virulence strategy of this broad-spectrum phytopathogen, the sequence of the linear plasmid of strain D188, pFiD188, was determined. Analysis of the 198,917 bp revealed four syntenic regions with linear plasmids of R.

Plant-derived auxin plays an accessory role in symptom development upon Rhodococcus fascians infection.

The biotrophic phytopathogen Rhodococcus fascians has a profound impact on plant development, mainly through its principal virulence factors, a mix of synergistically acting cytokinins that induce shoot formation. Expression profiling of marker genes for several auxin biosynthesis routes and mutant analysis demonstrated that the bacterial cytokinins stimulate the auxin biosynthesis of plants via specific targeting of the indole-3-pyruvic acid (IPA) pathway, resulting in enhanced auxin signaling in infected tissues. The double mutant tryptophan aminotransferase 1-1 tryptophan aminotransferase related 2-1 (taa1-1 tar2-1) of Arabidopsis (Arabidopsis thaliana), in which the IPA pathway is defective, displayed a decreased responsiveness towards R.

Nodule numbers are governed by interaction between CLE peptides and cytokinin signaling.

CLE peptides are involved in the balance between cell division and differentiation throughout plant development, including nodulation. Previously, two CLE genes of Medicago truncatula, MtCLE12 and MtCLE13, had been identified whose expression correlated with nodule primordium formation and meristem establishment. Gain-of-function analysis indicated that both MtCLE12 and MtCLE13 interact with the SUPER NUMERIC NODULES (SUNN)-dependent auto-regulation of nodulation to control nodule numbers.

Identification of putative CLE peptide receptors involved in determinate nodulation on soybean.

CLAVATA3/EMBRYO SURROUNDING REGION (CLE) peptides tightly control the balance between stem cell proliferation and differentiation in several plant developmental processes. Transmission of the CLE peptide signal has been shown to be rather complex. Despite their recent identification, little is known about the receptors by which nodulation-specific CLE peptides, which were identified in soybean, are perceived.

Never too many? How legumes control nodule numbers.

Restricted availability of nitrogen compounds in soils is often a major limiting factor for plant growth and productivity. Legumes circumvent this problem by establishing a symbiosis with soil-borne bacteria, called rhizobia that fix nitrogen for the plant. Nitrogen fixation and nutrient exchange take place in specialized root organs, the nodules, which are formed by a coordinated and controlled process that combines bacterial infection and organ formation.

Transcriptional and post-transcriptional regulation of a NAC1 transcription factor in Medicago truncatula roots.

• Legume roots develop two types of lateral organs, lateral roots and nodules. Nodules develop as a result of a symbiotic interaction with rhizobia and provide a niche for the bacteria to fix atmospheric nitrogen for the plant. • The Arabidopsis NAC1 transcription factor is involved in lateral root formation, and is regulated post-transcriptionally by miRNA164 and by SINAT5-dependent ubiquitination.

A successful bacterial coup d'état: how Rhodococcus fascians redirects plant development.

Rhodococcus fascians is a gram-positive phytopathogen that induces differentiated galls, known as leafy galls, on a wide variety of plants, employing virulence genes located on a linear plasmid. The pathogenic strategy consists of the production of a mixture of six synergistically acting cytokinins that overwhelm the plant's homeostatic mechanisms, ensuring the activation of a signaling cascade that targets the plant cell cycle and directs the newly formed cells to differentiate into shoot meristems. The shoots that are formed upon infection remain immature and never convert to source tissues resulting in the establishment of a nutrient sink that is a niche for the epiphytic and endophytic R.

Bacterial and plant signal integration via D3-type cyclins enhances symptom development in the Arabidopsis-Rhodococcus fascians interaction.

The phytopathogenic actinomycete Rhodococcus fascians drives its host to form a nutrient-rich niche by secreting a mixture of cytokinins that triggers plant cell division and shoot formation. The discrepancy between the relatively low amount of secreted cytokinins and the severe impact of R. fascians infection on plant development has puzzled researchers for a long time.

Search for nodulation-related CLE genes in the genome of Glycine max.

CLE peptides are potentially involved in nodule organ development and in the autoregulation of nodulation (AON), a systemic process that restricts nodule number. A genome-wide survey of CLE peptide genes in the soybean glycine max genome resulted in the identification of 39 GmCLE genes, the majority of which have not yet been annotated. qRT-PCR analysis indicated two different nodulation-related CLE expression patterns, one linked with nodule primordium development and a new one linked with nodule maturation.

Rhodococcus fascians impacts plant development through the dynamic fas-mediated production of a cytokinin mix.

The phytopathogenic actinomycete Rhodococcus fascians D188 relies mainly on the linear plasmid-encoded fas operon for its virulence. The bacteria secrete six cytokinin bases that synergistically redirect the developmental program of the plant to stimulate proliferation of young shoot tissue, thus establishing a leafy gall as a niche. A yeast-based cytokinin bioassay combined with cytokinin profiling of bacterial mutants revealed that the fas operon is essential for the enhanced production of isopentenyladenine, trans-zeatin, cis-zeatin, and the 2-methylthio derivatives of the zeatins.

Transcription factor MtATB2: about nodulation, sucrose and senescence.

The symbiotic interaction between legumes and rhizobia results in root nodules with nitrogen-fixing bacteroids. Throughout the lifespan of the nodules, the exchange of C sources and N compounds between the host plant and the bacteria is tightly balanced. Sucrose plays a major role in the provision of C skeletons and energy to the bacteroids.

CLE peptides control Medicago truncatula nodulation locally and systemically.

The CLAVATA3/embryo-surrounding region (CLE) peptides control the fine balance between proliferation and differentiation in plant development. We studied the role of CLE peptides during indeterminate nodule development and identified 25 MtCLE peptide genes in the Medicago truncatula genome, of which two genes, MtCLE12 and MtCLE13, had nodulation-related expression patterns that were linked to proliferation and differentiation. MtCLE13 expression was up-regulated early in nodule development.

Comparison of developmental and stress-induced nodule senescence in Medicago truncatula.

Mature indeterminate Medicago truncatula nodules are zonated with an apical meristem, an infection zone, a fixation zone with nitrogen-fixing bacteroids, and a "developmental" senescence zone that follows nodule growth with a conical front originating in the center of the fixation zone. In nitrogen-fixing cells, senescence is initiated coincidently with the expression of a family of conserved cysteine proteases that might be involved in the degradation of symbiotic structures. Environmental stress, such as prolonged dark treatment, interferes with nodule functioning and triggers a fast and global nodule senescence.

Sesbania rostrata: a case study of natural variation in legume nodulation.

Legumes acquired the ability to engage in a symbiotic interaction with soil-borne bacteria and establish a nitrogen-fixing symbiosis in a novel root organ, the nodule. Most legume crops and the model legumes Medicago truncatula and Lotus japonicus are infected intracellularly in root hairs via infection threads that lead the bacteria towards a nodule primordium in the root cortex. This infection process, however, does not reflect the great diversity of infection strategies that are used by leguminous plants.

Water-tolerant legume nodulation.

Water-tolerant nodulation is an adaptation of legumes that grow in wet or temporarily flooded habitats. This nodulation mode takes place at lateral root bases via intercellular bacterial invasion in cortical infection pockets. The tropical legume Sesbania rostrata has become a model for the study of the molecular basis of crack entry nodulation compared with root hair curl nodulation.

The Gram-positive side of plant-microbe interactions.

Plant growth and development are significantly influenced by the presence and activity of microorganisms. To date, the best-studied plant-interacting microbes are Gram-negative bacteria, but many representatives of both the high and low G+C Gram-positives have excellent biocontrol, plant growth-promoting and bioremediation activities. Moreover, actinorhizal symbioses largely contribute to the global biological nitrogen fixation and many Gram-positive bacteria promote other types of symbioses in tripartite interactions.

(Homo)glutathione depletion modulates host gene expression during the symbiotic interaction between Medicago truncatula and Sinorhizobium meliloti.

Under nitrogen-limiting conditions, legumes interact with symbiotic rhizobia to produce nitrogen-fixing root nodules. We have previously shown that glutathione and homoglutathione [(h)GSH] deficiencies impaired Medicago truncatula symbiosis efficiency, showing the importance of the low M(r) thiols during the nodulation process in the model legume M. truncatula.

Calcium spiking patterns and the role of the calcium/calmodulin-dependent kinase CCaMK in lateral root base nodulation of Sesbania rostrata.

Nodulation factor (NF) signal transduction in the legume-rhizobium symbiosis involves calcium oscillations that are instrumental in eliciting nodulation. To date, Ca2+ spiking has been studied exclusively in the intracellular bacterial invasion of growing root hairs in zone I. This mechanism is not the only one by which rhizobia gain entry into their hosts; the tropical legume Sesbania rostrata can be invaded intercellularly by rhizobia at cracks caused by lateral root emergence, and this process is associated with cell death for formation of infection pockets.

Identification of Rhodococcus fascians cytokinins and their modus operandi to reshape the plant.

Decades ago, the importance of cytokinins (CKs) during Rhodococcus fascians pathology had been acknowledged, and an isopentenyltransferase gene had been characterized in the fas operon of the linear virulence plasmid, but hitherto, no specific CK(s) could be associated with virulence. We show that the CK receptors AHK3 and AHK4 of Arabidopsis thaliana are essential for symptom development, and that the CK perception machinery is induced upon infection, underlining its central role in the symptomatology. Three classical CKs [isopentenyladenine, trans-zeatin, and cis-zeatin (cZ)] and their 2-methylthio (2MeS)-derivatives were identified by CK profiling of both the pathogenic R.

Eternal youth, the fate of developing Arabidopsis leaves upon Rhodococcus fascians infection.

The phytopathogenic actinomycete Rhodococcus fascians induces neoplastic shooty outgrowths on infected hosts. Upon R. fascians infection of Arabidopsis (Arabidopsis thaliana), leaves are formed with small narrow lamina and serrated margins.

An integrated genomics approach to define niche establishment by Rhodococcus fascians.

Rhodococcus fascians is a Gram-positive phytopathogen that induces shooty hyperplasia on its hosts through the secretion of cytokinins. Global transcriptomics using microarrays combined with profiling of primary metabolites on infected Arabidopsis (Arabidopsis thaliana) plants revealed that this actinomycete modulated pathways to convert its host into a niche. The transcript data demonstrated that R.

Seven in absentia proteins affect plant growth and nodulation in Medicago truncatula.

Protein ubiquitination is a posttranslational regulatory process essential for plant growth and interaction with the environment. E3 ligases, to which the seven in absentia (SINA) proteins belong, determine the specificity by selecting the target proteins for ubiquitination. SINA proteins are found in animals as well as in plants, and a small gene family with highly related members has been identified in the genome of rice (Oryza sativa), Arabidopsis (Arabidopsis thaliana), Medicago truncatula, and poplar (Populus trichocarpa).

The genome of the versatile nitrogen fixer Azorhizobium caulinodans ORS571.

Background: Biological nitrogen fixation is a prokaryotic process that plays an essential role in the global nitrogen cycle. Azorhizobium caulinodans ORS571 has the dual capacity to fix nitrogen both as free-living organism and in a symbiotic interaction with Sesbania rostrata. The host is a fast-growing, submergence-tolerant tropical legume on which A.