Zinc mediates control of nitrogen fixation via transcription factor filamentation.

Plants adapt to fluctuating environmental conditions by adjusting their metabolism and gene expression to maintain fitness. In legumes, nitrogen homeostasis is maintained by balancing nitrogen acquired from soil resources with nitrogen fixation by symbiotic bacteria in root nodules. Here we show that zinc, an essential plant micronutrient, acts as an intracellular second messenger that connects environmental changes to transcription factor control of metabolic activity in root nodules.

Single-cell analysis identifies genes facilitating rhizobium infection in Lotus japonicus.

Legume-rhizobium signaling during establishment of symbiotic nitrogen fixation restricts rhizobium colonization to specific cells. A limited number of root hair cells allow infection threads to form, and only a fraction of the epidermal infection threads progress to cortical layers to establish functional nodules. Here we use single-cell analysis to define the epidermal and cortical cell populations that respond to and facilitate rhizobium infection.

A simple and efficient protocol for generating transgenic hairy roots using Agrobacterium rhizogenes.

For decades, Agrobacterium rhizogenes (now Rhizobium rhizogenes), the causative agent of hairy root disease, has been harnessed as an interkingdom DNA delivery tool for generating transgenic hairy roots on a wide variety of plants. One of the strategies involves the construction of transconjugant R. rhizogenes by transferring gene(s) of interest into previously constructed R.

Aromatic amino acid biosynthesis impacts root hair development and symbiotic associations in Lotus japonicus.

Legume roots can be symbiotically colonized by arbuscular mycorrhizal (AM) fungi and nitrogen-fixing bacteria. In Lotus japonicus, the latter occurs intracellularly by the cognate rhizobial partner Mesorhizobium loti or intercellularly with the Agrobacterium pusense strain IRBG74. Although these symbiotic programs show distinctive cellular and transcriptome signatures, some molecular components are shared.

A glycan receptor kinase facilitates intracellular accommodation of arbuscular mycorrhiza and symbiotic rhizobia in the legume Lotus japonicus.

Receptors that distinguish the multitude of microbes surrounding plants in the environment enable dynamic responses to the biotic and abiotic conditions encountered. In this study, we identify and characterise a glycan receptor kinase, EPR3a, closely related to the exopolysaccharide receptor EPR3. Epr3a is up-regulated in roots colonised by arbuscular mycorrhizal (AM) fungi and is able to bind glucans with a branching pattern characteristic of surface-exposed fungal glucans.

Nitrate restricts nodule organogenesis through inhibition of cytokinin biosynthesis in Lotus japonicus.

Legumes balance nitrogen acquisition from soil nitrate with symbiotic nitrogen fixation. Nitrogen fixation requires establishment of a new organ, which is a cytokinin dependent developmental process in the root. We found cytokinin biosynthesis is a central integrator, balancing nitrate signalling with symbiotic acquired nitrogen.

No Home without Hormones: How Plant Hormones Control Legume Nodule Organogenesis.

The establishment of symbiotic nitrogen fixation requires the coordination of both nodule development and infection events. Despite the evolution of a variety of anatomical structures, nodule organs serve a common purpose in establishing a localized area that facilitates efficient nitrogen fixation. As in all plant developmental processes, the establishment of a new nodule organ is regulated by plant hormones.

Insights into the evolution of symbiosis gene copy number and distribution from a chromosome-scale Lotus japonicus Gifu genome sequence.

Lotus japonicus is a herbaceous perennial legume that has been used extensively as a genetically tractable model system for deciphering the molecular genetics of symbiotic nitrogen fixation. Our aim is to improve the L. japonicus reference genome sequence, which has so far been based on Sanger and Illumina sequencing reads from the L.

A Toolkit for High Resolution Imaging of Cell Division and Phytohormone Signaling in Legume Roots and Root Nodules.

Legume plants benefit from a nitrogen-fixing symbiosis in association with rhizobia hosted in specialized root nodules. Formation of root nodules is initiated by organogenesis and coordinated infection of these developing lateral root organs by rhizobia. Both bacterial infection and nodule organogenesis involve cell cycle activation and regulation by auxin and cytokinin is tightly integrated in the process.

Atypical Receptor Kinase RINRK1 Required for Rhizobial Infection But Not Nodule Development in .

During the legume-rhizobium symbiotic interaction, rhizobial invasion of legumes is primarily mediated by a plant-made tubular invagination called an infection thread (IT). Here, we identify a gene in encoding a Leu-rich repeat receptor-like kinase (LRR-RLK), (), that is induced by Nod factors (NFs) and is involved in IT formation but not nodule organogenesis. A paralog, RINRK2, plays a relatively minor role in infection.

Characterizing standard genetic parts and establishing common principles for engineering legume and cereal roots.

Plant synthetic biology and cereal engineering depend on the controlled expression of transgenes of interest. Most engineering in plant species to date has relied heavily on the use of a few, well-established constitutive promoters to achieve high levels of expression; however, the levels of transgene expression can also be influenced by the use of codon optimization, intron-mediated enhancement and varying terminator sequences. Most of these alternative approaches for regulating transgene expression have only been tested in small-scale experiments, typically testing a single gene of interest.

Systemic control of legume susceptibility to rhizobial infection by a mobile microRNA.

Nitrogen-fixing root nodules on legumes result from two developmental processes, bacterial infection and nodule organogenesis. To balance symbiosis and plant growth, legume hosts restrict nodule numbers through an inducible autoregulatory process. Here, we present a mechanism where repression of a negative regulator ensures symbiotic susceptibility of uninfected roots of the host We show that microRNA miR2111 undergoes shoot-to-root translocation to control rhizobial infection through posttranscriptional regulation of the symbiosis suppressor TOO MUCH LOVE in roots.

Epidermal auxin biosynthesis facilitates rhizobial infection in Lotus japonicus.

Symbiotic nitrogen fixation in legumes requires nodule organogenesis to be coordinated with infection by rhizobia. The plant hormone auxin influences symbiotic infection, but the precise timing of auxin accumulation and the genetic network governing it remain unclear. We used a Lotus japonicus optimised variant of the DII-based auxin accumulation sensor and identified a rapid accumulation of auxin in the epidermis, specifically in the root hair cells.

Dynamics of Ethylene Production in Response to Compatible Nod Factor.

Establishment of symbiotic nitrogen-fixation in legumes is regulated by the plant hormone ethylene, but it has remained unclear whether and how its biosynthesis is regulated by the symbiotic pathway. We established a sensitive ethylene detection system for and found that ethylene production increased as early as 6 hours after inoculation with This ethylene response was dependent on Nod factor production by compatible rhizobia. Analyses of nodulation mutants showed that perception of Nod factor was required for ethylene emission, while downstream transcription factors including CYCLOPS, NIN, and ERN1 were not required for this response.

Cytokinin Biosynthesis Promotes Cortical Cell Responses during Nodule Development.

Legume mutants have shown the requirement for receptor-mediated cytokinin signaling in symbiotic nodule organogenesis. While the receptors are central regulators, cytokinin also is accumulated during early phases of symbiotic interaction, but the pathways involved have not yet been fully resolved. To identify the source, timing, and effect of this accumulation, we followed transcript levels of the cytokinin biosynthetic pathway genes in a sliding developmental zone of roots.

Different Pathways Act Downstream of the CEP Peptide Receptor CRA2 to Regulate Lateral Root and Nodule Development.

C-TERMINALLY ENCODED PEPTIDEs (CEPs) control root system architecture in a non-cell-autonomous manner. In Medicago truncatula, MtCEP1 affects root development by increasing nodule formation and inhibiting lateral root emergence by unknown pathways. Here, we show that the MtCEP1 peptide-dependent increase in nodulation requires the symbiotic signaling pathway and ETHYLENE INSENSITIVE2 (EIN2)/SICKLE (SKL), but acts independently of SUPER NUMERIC NODULES.

CYTOKININ OXIDASE/DEHYDROGENASE3 Maintains Cytokinin Homeostasis during Root and Nodule Development in Lotus japonicus.

Cytokinins are required for symbiotic nodule development in legumes, and cytokinin signaling responses occur locally in nodule primordia and in developing nodules. Here, we show that the Lotus japonicus Ckx3 cytokinin oxidase/dehydrogenase gene is induced by Nod factor during the early phase of nodule initiation. At the cellular level, pCkx3::YFP reporter-gene studies revealed that the Ckx3 promoter is active during the first cortical cell divisions of the nodule primordium and in growing nodules.

The value of biodiversity in legume symbiotic nitrogen fixation and nodulation for biofuel and food production.

Much of modern agriculture is based on immense populations of genetically identical or near-identical varieties, called cultivars. However, advancement of knowledge, and thus experimental utility, is found through biodiversity, whether naturally-found or induced by the experimenter. Globally we are confronted by ever-growing food and energy challenges.

The soybean (Glycine max) nodulation-suppressive CLE peptide, GmRIC1, functions interspecifically in common white bean (Phaseolus vulgaris), but not in a supernodulating line mutated in the receptor PvNARK.

Legume plants regulate the number of nitrogen-fixing root nodules they form via a process called the Autoregulation of Nodulation (AON). Despite being one of the most economically important and abundantly consumed legumes, little is known about the AON pathway of common bean (Phaseolus vulgaris). We used comparative- and functional-genomic approaches to identify central components in the AON pathway of common bean.

Structure-function analysis of the GmRIC1 signal peptide and CLE domain required for nodulation control in soybean.

Legumes control the nitrogen-fixing root nodule symbiosis in response to external and internal stimuli, such as nitrate, and via systemic autoregulation of nodulation (AON). Overexpression of the CLV3/ESR-related (CLE) pre-propeptide-encoding genes GmNIC1 (nitrate-induced and acting locally) and GmRIC1 (Bradyrhizobium-induced and acting systemically) suppresses soybean nodulation dependent on the activity of the nodulation autoregulation receptor kinase (GmNARK). This nodule inhibition response was used to assess the relative importance of key structural components within and around the CLE domain sequences of these genes.

Transient Nod factor-dependent gene expression in the nodulation-competent zone of soybean (Glycine max [L.] Merr.) roots.

All lateral organ development in plants, such as nodulation in legumes, requires the temporal and spatial regulation of genes and gene networks. A total mRNA profiling approach using RNA-seq to target the specific soybean (Glycine max) root tissues responding to compatible rhizobia [i.e.

Identification of systemic responses in soybean nodulation by xylem sap feeding and complete transcriptome sequencing reveal a novel component of the autoregulation pathway.

Establishment of the nitrogen-fixing nodulation symbiosis between legumes and rhizobia requires plant-wide reprogramming to allow infection and development of nodules. Nodulation is regulated principally via a mechanism called autoregulation of nodulation (AON). AON is dependent on shoot and root factors and is maintained by the nodulation autoregulation receptor kinase (NARK) in soybean.