Plant Cell Wall Remodelling in the Rhizobium–Legume Symbiosis

Brewin, N. J.

doi:10.1080/07352680490480734

Cited by 304 publications

(307 citation statements)

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“…Interactions between plant cell-wall material and other components of the infection thread matrix might play an important part in infection thread growth 48 . Plant cell wall remodelling during root hair colonization and infection thread formation is another process that is not well understood, but is proposed to involve plant proteins that are exported to the cell wall and the infection thread matrix 48 . Plant glycoproteins that are associated with the infection thread matrix become crosslinked, probably by reactive oxygen species (ROS) generated in the infection thread [49][50][51] .…”

Section: Sinorhizobium Meliloti Succinoglycan Biosynthesismentioning

confidence: 99%

“…Each bacterial cell is endocytosed by a target cell in an individual, unwalled membrane compartment that originates from the infection thread 48 . The entire unit, consisting of an individual bacterium and the surrounding endocytic membrane, is known as the symbiosome 48 . In indeterminate nodules, a bacterial cell and its surrounding membrane divide synchronously before the bacteria differentiate into nitrogenfixing bacteroids 69 .…”

Section: Endocytosis Of Rhizobiamentioning

confidence: 99%

“…As the infection thread develops, the inside of this tubule is topologically outside the root hair cell and possesses a plant cell wall 48 . Interactions between plant cell-wall material and other components of the infection thread matrix might play an important part in infection thread growth 48 . Plant cell wall remodelling during root hair colonization and infection thread formation is another process that is not well understood, but is proposed to involve plant proteins that are exported to the cell wall and the infection thread matrix 48 .…”

Section: Sinorhizobium Meliloti Succinoglycan Biosynthesismentioning

confidence: 99%

“…Plant glycoproteins that are associated with the infection thread matrix become crosslinked, probably by reactive oxygen species (ROS) generated in the infection thread [49][50][51] . One hypothesis is that solidification of the infection thread matrix, as a result of this crosslinking, generates a mechanical force that helps the ingrowth of the infection thread to proceed 48 . The production of ROS by plants is often part of a defence response against invading pathogens and it can also serve as an activating signal for other plant defences (see below) 52 .…”

Section: Sinorhizobium Meliloti Succinoglycan Biosynthesismentioning

confidence: 99%

“…In these cells, a network of microtubules connects the nucleus to the tip of the infection thread and surrounds the infection thread itself 8 . As the infection thread develops, the inside of this tubule is topologically outside the root hair cell and possesses a plant cell wall 48 . Interactions between plant cell-wall material and other components of the infection thread matrix might play an important part in infection thread growth 48 .…”

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How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

et al. 2007

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Nitrogen-fixing rhizobial bacteria and leguminous plants have evolved complex signal exchange mechanisms that allow a specific bacterial species to induce its host plant to form invasion structures through which the bacteria can enter the plant root. Once the bacteria have been endocytosed within a host-membrane-bound compartment by root cells, the bacteria differentiate into a new form that can convert atmospheric nitrogen into ammonia. Bacterial differentiation and nitrogen fixation are dependent on the microaerobic environment and other support factors provided by the plant. In return, the plant receives nitrogen from the bacteria, which allows it to grow in the absence of an external nitrogen source. Here, we review recent discoveries about the mutual recognition process that allows the model rhizobial symbiont Sinorhizobium meliloti to invade and differentiate inside its host plant alfalfa (Medicago sativa) and the model host plant barrel medic (Medicago truncatula).The recent completion of the Sinorhizobium meliloti genome sequence, and the progress towards the completion of the Medicago truncatula genome sequence, have led to a surge in the molecular characterization of the determinants that are involved in the development of the symbiosis between rhizobial bacteria and leguminous plants. Aromatic compounds from legumes called flavonoids first signal the rhizobial bacteria to produce lipochitooligosaccharide compounds called Nod factors 1 . Nod factors that are secreted by the bacteria activate multiple responses in the host plant that prepare the plant to receive the invading bacteria. Nod factors and symbiotic exopolysaccharides induce the plant to form infection threads, which are thin tubules filled with bacteria that penetrate into the plant cortical tissue and deliver the bacteria to their target cells. Plant cells in the inner cortex internalize the invading bacteria in host-membrane-bound compartments that mature into structures known Correspondence to G.C.W. gwalker@mit.edu. Competing interests statementThe authors declare no competing financial interests. DATABASES Invasion of plant rootsAlthough plant roots are exposed to various micro-organisms in the soil, their cell walls form a strong protective barrier against most harmful species. The early steps in the invasion of barrel medic (M. truncatula) and alfalfa (Medicago sativa) roots by S. meliloti are characterized by the reciprocal exchange of signals that allow the bacteria to use the plant root hair cells as a means of entry. Initial signal exchangeFlavonoid compounds (2-phenyl-1,4-benzopyrone derivatives) produced by leguminous plants are the first signals to be exchanged by host-rhizobial symbiont pairs 1 (FIG. 1). Flavonoids bind bacterial NodD proteins, which are members of the LysR family of transcriptional regulators, and activate these proteins to induce the transcription of rhizobial genes 1,2 . For example, the M. sativa-derived flavonoid luteolin stimulates binding of an active form of NodD1 to an S. meliloti 'nod-box' p...

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Section: Sinorhizobium Meliloti Succinoglycan Biosynthesismentioning

confidence: 99%

Section: Endocytosis Of Rhizobiamentioning

confidence: 99%

Section: Sinorhizobium Meliloti Succinoglycan Biosynthesismentioning

confidence: 99%

Section: Sinorhizobium Meliloti Succinoglycan Biosynthesismentioning

confidence: 99%

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How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

et al. 2007

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Root Nodules (Legume–RhizobiumSymbiosis)

Brewin

2010

Encyclopedia of Life Sciences

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Root nodule symbiosis enables nitrogen‐fixing bacteria to convert atmospheric nitrogen into a form that is directly available for plant growth. Biological nitrogen fixation provides a built‐in supply of nitrogen fertiliser for many legume crops such as peas, beans and clover. Legumes (Fabales) interact with single‐celled Gram‐negative bacteria, collectively termed rhizobia, whereas members of three other Rosid orders (Fagales, Cucurbitales and Rosales) interact with Gram‐positive filamentous actinobacteria of the genus Frankia . In legumes, infection proceeds through intercellular and trans‐cellular channels termed infection threads. At the same time, cells in the root cortex are induced to divide and generate the tissues of the nodule. Nitrogen fixation normally takes place within specialised bacteroid cells enclosed within organelle‐like cytoplasmic compartments termed symbiosomes. The anatomy and physiology of root nodules both reflect a high degree of structural and metabolic integration between plant and microbial symbionts. Key Concepts: Legumes (family Fabales) develop root nodules that harbour Rhizobium bacteria (rhizobia). Endosymbiotic bacteria (bacteroids) convert nitrogen to ammonia (biological nitrogen fixation). Legume crops restore fertility to agricultural soils by capturing nitrogen from the atmosphere. The legume– Rhizobium symbiosis provides one‐fifth of all nitrogen inputs into global agriculture. Symbiosis is based on metabolic exchange for mutual benefit: exchanges of oxygen, carbon and nitrogen are tightly regulated. Legumes only form a nitrogen‐fixing symbiosis with single‐celled bacteria collectively termed Rhizobium . However, other (related) groups of flowering plants form a root nodule symbiosis with filamentous actinobacteria of the genus Frankia . Some of the invasion processes adopted by Rhizobium and Frankia are shared with a mineral‐scavenging symbiosis involving arbuscular mycorrhizal fungi that originated over 400 Ma. Colonisation of host cells by Rhizobium usually involves specialised invasion structures termed ‘infection threads’ and specialised organelle‐like compartments termed ‘symbiosomes’. During evolution, there has been horizontal transfer of the genes that specify the capability for nodulation and symbiotic nitrogen fixation between diverse groups of soil bacteria.

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Rhizobia

Downie¹

2007

Encyclopedia of Life Sciences

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Rhizobia are soil bacteria that enter into a symbiosis with leguminous plants, producing root outgrowths (nodules) within which the bacteria convert atmospheric nitrogen into ammonia, that is made available to the plants. Legume nodules develop as a result of signal exchange between the symbiotic partners and the rhizobia infect the nodules via specialized infection threads. The bacteria are released into plant cells within the nodule and develop into a specialized form which is primarily dedicated to the production of ammonia via the action of an enzyme called nitrogenase.

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Plant Cell Wall Remodelling in the Rhizobium–Legume Symbiosis

Cited by 304 publications

References 201 publications

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

Root Nodules (Legume–RhizobiumSymbiosis)

Rhizobia

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