Leghemoglobin is an oxygen-carrying phytoglobin found in the nitrogen-fixing root nodules of leguminous plants. It is produced by these plants in response to the roots being colonized by nitrogen-fixing bacteria, termed rhizobia, as part of the symbiotic interaction between plant and bacterium: roots not colonized by Rhizobium do not synthesise leghemoglobin. Leghemoglobin has close chemical and structural similarities to hemoglobin, and, like hemoglobin, is red in colour. It was originally thought that the heme prosthetic group for plant leghemoglobin was provided by the bacterial symbiont within symbiotic root nodules. However, subsequent work shows that the plant host strongly expresses heme biosynthesis genes within nodules, and that activation of those genes correlates with leghemoglobin gene expression in developing nodules.
Rhizobia are diazotrophic bacteria that fix nitrogen after becoming established inside the root nodules of legumes (Fabaceae). To express genes for nitrogen fixation, rhizobia require a plant host; they cannot independently fix nitrogen. In general, they are gram negative, motile, non-sporulating rods.
Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen. Rhizobium species form an endosymbiotic nitrogen-fixing association with roots of (primarily) legumes and other flowering plants.
Diazotrophs are bacteria and archaea that fix gaseous nitrogen in the atmosphere into a more usable form such as ammonia.
Ensifer meliloti are an aerobic, Gram-negative, and diazotrophic species of bacteria. S. meliloti are motile and possess a cluster of peritrichous flagella. S. meliloti fix atmospheric nitrogen into ammonia for their legume hosts, such as alfalfa. S. meliloti forms a symbiotic relationship with legumes from the genera Medicago, Melilotus and Trigonella, including the model legume Medicago truncatula. This symbiosis promotes the development of a plant organ, termed a root nodule. Because soil often contains a limited amount of nitrogen for plant use, the symbiotic relationship between S. meliloti and their legume hosts has agricultural applications. These techniques reduce the need for inorganic nitrogenous fertilizers.
Nod factors, are signaling molecules produced by soil bacteria known as rhizobia in response to flavonoid exudation from plants under nitrogen limited conditions. Nod factors initiate the establishment of a symbiotic relationship between legumes and rhizobia by inducing nodulation. Nod factors produce the differentiation of plant tissue in root hairs into nodules where the bacteria reside and are able to fix nitrogen from the atmosphere for the plant in exchange for photosynthates and the appropriate environment for nitrogen fixation. One of the most important features provided by the plant in this symbiosis is the production of leghemoglobin, which maintains the oxygen concentration low and prevents the inhibition of nitrogenase activity.
Frankia is a genus of nitrogen-fixing bacteria that live in symbiosis with actinorhizal plants, similar to the Rhizobium bacteria found in the root nodules of legumes in the family Fabaceae. Frankia also initiate the forming of root nodules.
The rhizosphere is the narrow region of soil or substrate that is directly influenced by root secretions and associated soil microorganisms known as the root microbiome. Soil pores in the rhizosphere can contain many bacteria and other microorganisms that feed on sloughed-off plant cells, termed rhizodeposition, and the proteins and sugars released by roots, termed root exudates. This symbiosis leads to more complex interactions, influencing plant growth and competition for resources. Much of the nutrient cycling and disease suppression by antibiotics required by plants occurs immediately adjacent to roots due to root exudates and metabolic products of symbiotic and pathogenic communities of microorganisms. The rhizosphere also provides space to produce allelochemicals to control neighbours and relatives.
Sharon Rugel Long is an American plant biologist. She is the Steere-Pfizer Professor of Biological Science in the Department of Biology at Stanford University, and the Principal Investigator of the Long Laboratory at Stanford.
Horizontal transmission is the transmission of organisms between biotic and/or abiotic members of an ecosystem that are not in a parent-progeny relationship. This concept has been generalized to include transmissions of infectious agents, symbionts, and cultural traits between humans.
Bradyrhizobium is a genus of Gram-negative soil bacteria, many of which fix nitrogen. Nitrogen fixation is an important part of the nitrogen cycle. Plants cannot use atmospheric nitrogen (N2); they must use nitrogen compounds such as nitrates.
Actinorhizal plants are a group of angiosperms characterized by their ability to form a symbiosis with the nitrogen fixing actinomycetota Frankia. This association leads to the formation of nitrogen-fixing root nodules.
Trophic mutualism is a key type of ecological mutualism. Specifically, "trophic mutualism" refers to the transfer of energy and nutrients between two species. This is also sometimes known as resource-to-resource mutualism. Trophic mutualism often occurs between an autotroph and a heterotroph. Although there are many examples of trophic mutualisms, the heterotroph is generally a fungus or bacteria. This mutualism can be both obligate and opportunistic.
Bradyrhizobium japonicum is a species of legume-root nodulating, microsymbiotic nitrogen-fixing bacteria. The species is one of many Gram-negative, rod-shaped bacteria commonly referred to as rhizobia. Within that broad classification, which has three groups, taxonomy studies using DNA sequencing indicate that B. japonicum belongs within homology group II.
enod40, also known as early nodulin 40, is a gene found in flowering plants. The gene has characteristics of both protein and Non-coding RNA genes. There is some evidence that the non-coding characteristics of this gene are more widely conserved than the protein coding sequences. In soyabeans enod40 was found to be expressed during early stages of formation of nitrogen-fixing root nodules that are associated with symbiotic soil rhizobial bacteria. The gene is also active in roots containing fungi forming phosphate-acquiring arbuscular mycorrhiza. An interaction with a novel RNA-binding protein MtRBP1 investigated in the development of Root nodule suggests ENOD40 has a function of cytoplasmic relocalization of nuclear proteins. In the study of non-legume plants, the over-expression of ENOD40 in transgenic Arabidopsis lines was observed a reduction of cell expansion.
Ensifer fredii is a nitrogen fixing bacterium. It is a fast-growing root nodule bacterium. Ensifer fredii exhibits a broad host-range and is able to nodulate both determinant hosts, such as soy, as well as indeterminate hosts including the pigeon pea. Because of their ease of host infection there is interest in their genetics and the symbiotic role in host infection and nodule formation.
Ensifer medicae is a species of gram-negative, nitrogen-fixing, rod-shaped bacteria. They can be free-living or symbionts of leguminous plants in root nodules. E.medicae was first isolated from root nodules on plants in the genus Medicago. Some strains of E.medicae, like WSM419, are aerobic. They are chemoorganotrophic mesophiles that prefer temperatures around 28 °C. In addition to their primary genome, these organisms also have three known plasmids, sized 1,570,951 bp, 1,245,408 bp and 219,313 bp.
Martin Parniske is a German biologist with a specialisation in genetics, microbiology and biochemistry. He is university professor and head of the Institute of Genetics at the Faculty of Biology of the Ludwig Maximilian University of Munich. Parniske's scientific focus is on the molecular interaction between plants and symbiotic and pathogenic organisms including bacteria, fungi, oomycetes and insects.
A symbiosome is a specialised compartment in a host cell that houses an endosymbiont in a symbiotic relationship.
Myriam Charpentier is a molecular biologist, who specialises in cell and developmental biology at the John Innes Centre, Norwich. Charpentier studies the environmental and biological stimulus of nuclear calcium signalling in plants.
