Bacterium background
Rhizobia, is a col ective name of the genera Rhizobium, Sinorhizobium,
and Bradyrhizobium, which are soil and rhizosphere bacteria
of agronomic importance because they perform nitrogen-fixing symbioses with
leguminous plants. Rhizobium and Sinorhizobium are in the family
Rhizobiaceae, while Mesorhizobium and Bradyrhizobium members of
Phyllobacteriaceae and Bradyrhizobiaceae, respectively.
Sinorhizobium meliloti, is a common Gram-negative soil and rhizosphere
bacterium, best known for its ability to induce the formation of nodules on the
roots of Medicago, Melilotus and Trigonel a sp. Inside the nodules,
differentiated bacteria cal ed bacteroids fix atmospheric nitrogen (ie reduce N2
into NH3) to the benefit of the plant. The S. meliloti genome contains three
replicons: a 3.65-Mb chromosome and two megaplasmids, pSyma (1.35 Mb)
and pSymb (1.68 Mb). Sinorhizobium meliloti strain 1021 was provided to
CAMBIA from the Australian National University Col ection (Canberra,
The strain Rhizobium sp. NGR234, is another Gram-negative soil and
rhizosphere bacterium, which is known to live in symbiosis with more than 110
genera of legumes as wel as the non-legume Parasponia andersoni.
Rhizobium sp. NGR234 has a chromosome 3.5 Mb in length, a megaplasmid
of more than 2 Mb (pNGR234b), and a smal er plasmid 536,165 bp in length
(pNGR234a) that carries most of the genes used for symbioses with legumes.
The 536,165-bp sequence of pNGR234a has now been completely analysed
and released to the public domain. Rhizobium sp. NGR234was provided to
CAMBIA from the Australian National University Col ection (Canberra,
Mesorhizobium loti is a member of rhizobia which is able to form determinant-
type globular nodules and perform nitrogen-fixation on several Lotus species.
The genome of M. loti consisted of a single chromosome (7,036,071 bp) and
two plasmids, designated as pMLa (351,911 bp ) and pMLb (208,315 bp).
Mesorhizobium loti MAFF303099 was obtained from University of Otago,
(Dunedin, NZ).
Ti Plasmid construction:
The modified Ti plasmids, were created using a suicide vector which was
constructed by T/A cloning of a PCR-amplified fragment from the Ti plasmid of
EHA105 into TOPO vector pCR2.1 (Invitrogen, CA) corresponding to 1316 bp
encompassing the virG gene (pTiWB1) or a 995 bp part of the non-essential
gene moaA (pTiWB3). The oriT fragment was cloned in this vector as an XbaI
fragment fol owing amplification from pSUP202. Electroporation of the suicide
vector into EHA105 resulted in integration of the whole vector by a single
crossing-over event, thereby creating two functional virG genes (pTiWB1) or
insertion of a second truncated moaA gene. Co-integration was confirmed by
PCR across the integration site and by Southern blotting showing duplication
of the target locus. The modified Ti plasmids were constructed at CAMBIA
(Canberra, Australia).
pCAMBIA1105.1R construction:
The binary vector pCAMBIA1105.1R, containing hygromycin
phosphotransferase (aph or HygR) and GUSPlus genes for expression in
plants, was derived from pCAMBIA1305.1 (GenBank no. AF354045) by
insertion of a spectinomycin/streptomycin marker into the SacII site and the
removal of the kanamycin marker. The spectinomycin/streptomycin marker
was generated by PCR amplification from pPZP200. In addition, the PvuII-
PvuII MCS fragment in pCAMBIA1305.1 was replaced by the 99bp larger
PvuII-PvuII MCS from pCR2.1. The binary vector was constructed at
CAMBIA (Canberra, Australia).
Bacterial strain construction:
The modified Ti plasmid (pTiWB3) was mobilised to Sinorhizobium meliloti in
a triparental mating with EHA105 (pTiWB3), and E. coli helper strain RP4-4
(carbenicil in and tetracycline resistance). The binary vector,
pCAMBIA1105.1R, was then introduced by electroporation. The bacterial
strain containing pTiWB3 and the binary vector pCAMBIA1105.1R was
constructed at CAMBIA (Canberra, Australia).
Differences between the modified and unmodified bacterium:
The modified bacterium, containing the Ti plasmid and the binary vector
pCAMBIA1105.1R, is able transfer a portion of DNA (cal ed T-DNA) from the
binary vector into a plant cel . Once in the plant cel , the T-DNA targets the
nucleus, al owing for integration into the plant genome and expression of
genes encoded on the T-DNA. The unmodified bacterium is unable to transfer
DNA to a plant host.
Shipping and safeguards against escape or dissemination: Bacterial
stabs wil be made onto YM media in a 2 ml polypropylene, screw top vial, the
vial wil be placed in a flat clear plastic holder and shipped in a bubble-wrap
envelope. Envelope size approximately 15 x 23 cm.


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