''Rhizobium rhizogenes'' (formerly ''Agrobacterium rhizogenes'') is a
Gram-negative
Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...
soil bacterium that produces hairy root disease in
dicotyledonous plants. ''R. rhizogenes'' induces the formation of proliferative multiple-branched adventitious roots at the site of infection, so-called 'hairy roots'.
In the
rhizosphere
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 microo ...
, plants may suffer from wounds by soil
pathogens
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...
or other sources. This leads to the secretion of
phenolic compounds like
acetosyringone
Acetosyringone is a phenolic natural product and a chemical compound related to acetophenone and 2,6-dimethoxyphenol. It was first described in relation to lignan/phenylpropanoid-type phytochemicals, with isolation from a variety of plant source ...
which have
chemotactic
Chemotaxis (from '' chemo-'' + '' taxis'') is the movement of an organism or entity in response to a chemical stimulus. Somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemica ...
effects that attract the bacteria. Under such conditions, certain bacterial genes are turned on leading to the transfer of its
T-DNA
The transfer DNA (abbreviated T-DNA) is the transferred DNA of the tumor-inducing (Ti) plasmid of some species of bacteria such as '' Agrobacterium tumefaciens'' and '' Agrobacterium rhizogenes(actually an Ri plasmid)''. The T-DNA is transferred ...
from its root-inducing plasmid (Ri plasmid) into the plant through the wound. After integration and expression, ''in vitro'' or under natural conditions, the hairy root
phenotype
In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological pr ...
is observed, which typically includes overdevelopment of a root system that is not completely
geotropic
Gravitropism (also known as geotropism) is a coordinated process of differential growth by a plant in response to gravity pulling on it. It also occurs in fungi. Gravity can be either "artificial gravity" or natural gravity. It is a general featu ...
, and altered (wrinkled) leaf morphology, if leaves are present.
Bacterial genes may be retained within the plant.
The
hairy roots are grown ''in vitro'' in
bioreactor
A bioreactor refers to any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical process is carried out which involves organisms or biochemically active substances ...
s to study their soil interaction with other pathogens like
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
and
nematodes. This technique has also led to the commercial production of certain metabolic compounds that the plant is known to secrete, especially in regard to the medicinal plants that are difficult to cultivate in sufficient quantities by other means.
The root cultures are also used for
genetic engineering.
References
{{Taxonbar, from=Q138216
Rhizobiaceae
Bacteria described in 2001