U.S. patent number RE37,287 [Application Number 09/025,042] was granted by the patent office on 2001-07-17 for chimeric gene for the transformation of plants.
This patent grant is currently assigned to Aventis Cropscience S.A.. Invention is credited to Michel Lebrun, Bernard Leroux, Alain Sailland.
United States Patent |
RE37,287 |
Lebrun , et al. |
July 17, 2001 |
Chimeric gene for the transformation of plants
Abstract
Chimeric gene for conferring to plants an increased tolerance to
a herbicide having as its target EPSPS comprises, in the direction
of transcription, a promoter region, a transit peptide region, a
coding sequence for glyphosate tolerance and a polyandenylation
signal region, wherein the transit peptide region comprises, in the
direction of translation, at least one transit peptide of a plant
gene encoding a plastid-localized enzyme and then a second transit
peptide of a plant gene encoding, a plastid-localized enzyme.
Production of glyphosate-tolerant plants is disclosed.
Inventors: |
Lebrun; Michel (Montpellier,
FR), Leroux; Bernard (Raleigh, NC), Sailland;
Alain (Lyons, FR) |
Assignee: |
Aventis Cropscience S.A.
(Lyons, FR)
|
Family
ID: |
9410557 |
Appl.
No.: |
09/025,042 |
Filed: |
February 17, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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251621 |
May 31, 1994 |
5510471 |
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846211 |
Mar 4, 1992 |
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Reissue of: |
477581 |
Jun 7, 1995 |
05633448 |
May 27, 1997 |
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Foreign Application Priority Data
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Mar 5, 1991 [FR] |
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91 02872 |
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Current U.S.
Class: |
800/278;
435/252.3; 435/320.1; 435/418; 435/419; 435/468; 536/23.2;
536/23.4; 536/23.7; 536/24.1; 800/300; 800/320.1 |
Current CPC
Class: |
C12N
15/8275 (20130101); C12N 15/62 (20130101); C07K
2319/08 (20130101) |
Current International
Class: |
C12N
15/82 (20060101); C12N 15/62 (20060101); A01H
005/00 (); C12N 005/04 (); C12N 015/82 () |
Field of
Search: |
;800/300,278,320.1
;435/320.1,252.3,69.1,468,418,419 ;536/24.1,23.4,23.2,23.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 189 707 B1 |
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Aug 1986 |
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EP |
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0 218 571 B1 |
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Apr 1987 |
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EP |
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0 337 899 |
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Oct 1989 |
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EP |
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WO 88/02402 |
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Apr 1988 |
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WO |
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.
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|
Primary Examiner: McElwain; Elizabeth F.
Attorney, Agent or Firm: Connolly, Bove, Lodge & Hutz
LLP
Parent Case Text
This is a divisional of application Ser. No. 08/251,621, filed on
May 31, 1994, now U.S. Pat. No. 5,510,471 which is a continuation
of Ser. No. 07/846,211, filed on Mar. 4, 1992, now abandoned.
Claims
We claim:
1. A chimeric gene for conferring to plants an increased tolerance
to glyphosate comprising, in the direction of transcription, a
promoter region, a DNA sequence encoding a first transit peptide
from a ribulose-1,5,-bisphosphate carboxylase small subunit, a DNA
sequence encoding an N-terminal domain of a mature
ribulose-1,5-bisphosphate carboxylase small subunit, a DNA sequence
encoding a second transit peptide from a ribulose-1,5,-bisphosphate
carboxylase small subunit, coding sequence for
5-(enolpyruvyl)shikimate-3-phosphate synthase and an untranslated
polyadenylation signal.
2. The chimeric gene according to claim 1 wherein the coding
sequence for 5-(enolpyruvyl)shikimate-3-phosphate synthase is of
bacterial origin.
3. The chimeric gene according to claim 1 wherein the coding
sequence for 5-(enolpyruvyl)shikimate-3-phosphate synthase is of
plant origin.
4. A vector for transforming plants, which comprises a chimeric
gene according to claim 1.
5. A vector for transforming plants, which comprises a chimeric
gene according to claim 2.
6. A vector for transforming plants, which comprises a chimeric
gene according to claim 3.
7. An Agrobacterium, which contains a vector according to claim
4.
8. An Agrobacterium, which contains a vector according to claim
5.
9. An agrobacterium, which contains a vector according to claim
6.
10. A transformed plant cell, which contains a chimeric gene
according to claim 1.
11. A transformed plant cell, which contains a chimeric gene
according to claim 2.
12. A transformed plant cell, which contains a chimeric gene
according to claim 3.
13. A transformed plant with improved glyphosate tolerance, which
was obtained by regeneration of the cell according to claim 10.
14. A transformed plant with improved glyphosate tolerance, which
was obtained by regeneration of the cell according to claim 11.
15. A transformed plant with improved glyphosate tolerance, which
was obtained by regeneration of the cell according to claim 12.
16. A plant according to claim 13, which is a dicotyledon.
17. A plant according to claim 13, which is a monocotyledon.
18. A process for constructing a chimeric gene according to claim
1, wherein sequences for at least two transit peptide regions, at
least one sequence of the N-terminal domain of a mature
ribulose-1,5-bisphosphate carboxylase small subunit, at least one
sequence encoding 5-(enolpyruvyl) shikimate-3phosphate synthase and
a polyadenylation signal region are each isolated, and wherein said
sequences are then assembled in the direction of transcription of
the 5-(enolpyruvyl) shikimate-3phosphate synthase gene.
19. A process for constructing a chimeric gene according to claim
2, wherein sequences for at least two transit peptide regions, at
least one sequence of the N-terminal domain of a mature
ribulose-1,5-bisphosphate carboxylase small subunit, at least one
sequence encoding 5-(enolpyruvyl) shikimate-3-phosphate synthase
and a polyadenylation signal region are each isolated, and wherein
said sequences are then assembled in the direction of transcription
of the 5-(enolpyruvyl) shikimate-3-phosphate synthase gene.
20. A process for constructing a chimeric gene according to claim
3, wherein sequences for at least two transit peptide regions, at
least one sequence of the N-terminal domain of a mature
ribulose-1,5-bisphosphate carboxylase small subunit, at least one
sequence encoding 5-(enolpyruvyl) shikimate-3-phosphate synthase
and a polyadenylation signal region are each isolated, and wherein
said sequences are then assembled in the direction of transcription
of the 5-(enolpyruvyl) shikimate-3-phosphate synthase
gene..Iadd.
21. An agronomic method comprising:
A) growing a plant which contains in its genome a nucleic acid
sequence encoding a polypeptide sufficient for localization of a
gene product in a chloroplast of a plant cell, which polypeptide
comprises in the direction of translation:
(i) a first chloroplast transit peptide of a
ribulose-1,5-bisphosphate carboxylase oxygenase small subunit;
(ii) an N-terminal domain from a mature ribulose-1,5-bisphosphate
carboxylase oxygenase small subunit; and
(iii) a second chloroplast transit peptide of a
ribulose-1,5-bisphosphate carboxylase oxygenase small subunit;
and further encoding a 5-(enolpyruvyl)shikimate-3-phosphate
synthase which renders said plant tolerant to a phosphonomethyl
glycine herbicide; and
B) applying said herbicide to the plant..Iaddend..Iadd.
22. The method of claim 21, wherein the plant is
maize..Iaddend..Iadd.
23. The method of claim 21, wherein the
5-(enolpyruvyl)shikimate-3-phosphate synthase is mutated, the
mutation being selected from the group consisting of Pro 101 to Ser
and Gly 96 to Ala..Iaddend..Iadd.
24. The method of claim 23, wherein the plant is maize..Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to novel transit peptide DNA
sequences, to novel chimeric genes and to their use in plants for
conferring to them an increased tolerance to herbicides in general
especially to those of the phosphonomethylglycine family. It also
relates to the plant cells transformed by means of these genes, to
the transformed plants regenerated from these cells as well as to
the plants derived from crossbreedings using these transformed
plants.
Glyphosate, sulfosate or fosametine are broad-spectrum systemic
herbicides of the phosphonomethyl-glycine family. They act
essentially as competitive inhibitors of
5-(enolpyruvyl)shikimate-3-phosphate synthase (EC 2.5.1.19) or
EPSPS in relation to PEP (phosphoenolpyruvate). After their
application to the plant, they are translocated inside the plant
where they accumulate in the rapidly growing parts, in particular
the caulinary and root apexes, causing the deterioration and even
the destruction of sensitive plants.
Plastidial EPSPS, the main target of these products, is an enzyme
of the aromatic amino acid biosynthesis pathway which is encoded by
one or more nuclear genes and synthesised in the form of a
cytoplasmic precursor and then imported into the plastids where it
accumulates in its natural form.
The tolerance of plants to glyphosate and to products of the family
is obtained by the stable introduction inside their genome of an
EPSPS gene of plant or bacterial origin mutant or nonmutant with
respect to the characteristics of the inhibition of the product of
this gene by glyphosate. Given the mode of action of glyphosate and
the degree of tolerance to glyphosate of the product of the genes
used, it is useful to be able to express the product of translation
of this gene so as to permit its substantial accumulation in
plastids.
It is known, for example from American Patent U.S. Pat. No.
4,535,060, to confer to a plant a tolerance to a herbicide of the
abovementioned type, in particular N-(phosphonomethyl)glycine or
glyphosate, by introducing into the plant genome a gene encoding an
EPSPS carrying at least one mutation making this enzyme more
resistant to its competitive inhibitor (glyphosate), after
localisation of the enzyme in the plastidial compartment. However,
these techniques need to be improved in order to achieve greater
reliability in the use of these plants under agronomic
conditions.
SUMMARY OF THE INVENTION
In the present description, "plant" is understood as meaning any
differentiated multicellular organism capable of photosynthesis and
"plant cell" any cell derived from a plant and capable of forming
undifferentiated tissues such as calluses or differentiated tissues
such as embryos or plant sections, plants or seeds.
The subject of the present invention is the production of
transformed plants having an increased tolerance to herbicides in
general and especially to those of the phosphonomethylglycine
family by regenerating cells transformed by means of novel chimeric
genes comprising a gene for tolerance to these herbicides. The
invention also relates to these novel chimeric genes, to the novel
transit peptides which they contain as well as to the plants
containing them which are made more tolerant by an accumulation of
the mutant enzyme, in its mature form, in the plants.
More particularly, the subject of the invention is a chimeric gene
for conferring to plants an increased tolerance to a herbicide
whose target is EPSPS, comprising, in the direction of
transcription, a promoter region, a transit peptide region, a
sequence of a gene encoding a glyphosate tolerance enzyme and an
untranslated polyadenylation signal region in 3', wherein the
transit peptide region comprises, in the direction of
transcription, a transit peptide of a plant gene encoding a
plastid-localised enzyme, a partial sequence of the N-terminal
mature pan of a plant gene encoding a plastid-localised enzyme and
then a second transit peptide of a plant gene encoding a
plastid-localised enzyme.
The invention also relates to any DNA sequence of the transit
peptide region defined above.
The transit peptides which can be used in the transit peptide
region may be known per se and may be of plant origin, for example,
derived from maize, sunflower, peas, tobacco or the like. The first
and the second transit peptides may be identical, analogous or
different. They may in addition each comprise one or more transit
peptide units. A sequence derived from the SSU of the ribulose
1,5-diphosphate carboxylase oxygenase (RuBisCO) gene is preferably
used.
The partial sequence of the N-terminal mature part is derived from
a plant gene encoding a plastid-localised enzyme, such as for
example a maize, sunflower or pea gene or the like, it being
possible for the original plant species to be identical, analogous
or different from that from which the first and second transit
peptides are derived respectively. Furthermore, the partial
sequence of the mature part may comprise a varying number of amino
acids, generally from 10 to 40, preferably from 18 to 33. A
sequence derived from the SSU of the ribulose 1,5-diphosphate
carboxylase oxygenase (RuBisCO) gene is preferably used.
Construction of the entire transit region may be carded out in a
manner known per se, in particular by fusion or any other suitable
means. The role of this characteristic region is to enable the
release of a mature, native protein with a maximum efficiency.
The coding sequence for herbicide tolerance which may be used in
the chimeric gene according to the invention encodes a mutant EPSPS
having a degree of glyphosate tolerance. This sequence, obtained in
particular by mutation of the EPSPS gene, may be of bacterial
origin, for example derived from Salmonella typhymurium (and called
in the text which follows "AroA gene"), or of plant origin, for
example from petunia or from tomatoes. This sequence may comprise
one or more mutations, for example the Pro 101 to Ser mutation or
alternatively the Gly 96 to Ala mutations.
The promoter region of the chimeric gene according to the invention
may consist advantageously of at least one promoter on a fragment
thereof of a gene which is expressed naturally in plants, that is
to say promoters of vital origin such as that of 35S RNA of the
cauliflower mosaic virus (CaMV35S) or of plant origin such as the
small subunit of the ribulose 1,5-diphosphate carboxylase (RuBisCO)
gene of a crop such as maize or sunflower.
The untranslated polyadenylation signal region in 3' of the
chimeric gene according to the invention may be of any origin, for
example bacterial, such as the nopaline synthase gene, or of plant
origin, such as the small subunit of the maize or sunflower
RuBisCO.
The chimeric gene according to the invention may comprise, in
addition to the above essential pans, an untranslated intermediate
region (linker) between the promoter region and the coding sequence
which may be of any origin, bacterial, vital or plant.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
EXAMPLE 1: CONSTRUCTION OF A CHIMERIC GENE
The construction of the chimeric gene according to the invention is
carried out using the following elements:
1) "Double CaMV" promoter (that is to say pan of which has been
duplicated):
The CaMV35S promoter was isolated by Odell et al. (1985). A clone,
pJO 5-2, containing about 850 bp upstream of the site of initiation
of transcription was cut with EcoRI-HindIII, the ends of this
isolated fragment were made blunt using Klenow polymerase and the
fragment inserted at the HincII site of the vector pUC19
(Yannish-Perron et al., 1985). This promoter was digested with
ClaI, the ends filled using Klenow polymerase and then redigested
with HindIII. A HindIII-EcoRV fragment, isolated from the same
initial promoter, was introduced between these two sites. The
promoter thus obtained possesses a double amplification region
upstream of the regulatory elements of the CaMV35S promoter. It was
introduced in the form of a HindIII-EcoRI fragment into the vector
pRPA-BL 150 A alpha 2, described in French Patent Application
88/04130, cut with HindIII and EcoRI.
2) Transfer region: the two transit peptides as well as the mature
protein elements used are derived from the cloned cDNA of the small
subunit of the gene of maize RuBisCO whose gene has been described
by Lebrun et at. (1987), and from the cloned cDNA of the small
subunit of the gene of sunflower RuBisCO, isolated by Waksman et
at, (1987). More specifically, the transit region, called optimised
transit peptide, comprises, in the direction of translation:
a transit peptide of the small subunit of sunflower RuBisCO,
an N-terminal sequence of 22 amino acids of the mature part of the
small subunit of maize RuBisCO,
a transit peptide of the small subunit of maize RuBisCO.
The construct using this optimised transfer peptide is called
pRPA-BL 410.
Other similar sequences may be used which contain sequences of 10
to 40 and preferably 18 and 33 amino acids respectively.
In order to provide a comparative element, another construction was
carried out using a first transit peptide and the same mature
sequence part but without a second transit peptide, according to
the prior art (pRPA-BL 294).
3) Structural gene: it is derived from the mutant gene at the
position (Pro 101 to Ser) of EPSPS of Salmonella typhymurium
isolated by Stalker et al, (1985). The pMG34-2 clone (provided by
Calgene) was linearised with XbaI and then treated with Vigna
radiata nuclease. After recurring with SmaI, the two blunt ends
were ligated. The clone obtained possesses an NcoI site in the
initiator ATG as well as a 17-bp SaII site downstream of the stop
codon. This clone was called pRPA-BL 104.
4) Polyadenylation signal region: the fragment is derived from the
nopaline synthase gene of pTi37 (Bevan et al., 1983). This site is
contained in a 260-bp MboI fragment (Fraley et at., 1983; Patent
Application PCT 84/02913) which was treated with Klenow polymerase
and cloned in the SmaI site of M13 mp 18 in order to introduce the
BamHI and EcoRI sites at the 5' and 3' ends respectively.
After cutting with BamHI and treating with Vigna radiata nuclease
followed by cutting with EcoRI and treating with Klenow polymerase,
the resulting fragment was introduced in the vector p-BL 20 (cf.
French Patent Application 88/04130), cut by XbaI and BamHI and
treated with Klenow polymerase. After recutting with SaII and SstI,
a fragment of about 0.4 kbp containing the 3' nos sequence on the
side of the SaII site and the fight end on the T-DNA side of the
SstI site is obtained.
The assembly of the various elements was carried out in the
following manner:
"Transit peptide of the SSU of the maize RuBisCO/AroA gene"
fusion:
The transit peptide of the SSU of the maize RuBisCO gene is derived
from a 192-bp EcoRI-SphI fragment obtained from the cDNA
corresponding to the SSU gene of the maize RuBisCO gene, described
by Lebrun et al. (1987), possessing an NcoI site spanning the
initiation codon for translation and an SphI site corresponding to
the cleavage site of the transit peptide.
Translational fusion is obtained between the maize transit peptide
and the bacterial EPSPS gene by treating the SphI end with
bacteriophage T4 polymerase and by ligating it with the Klenow
polymerase-treated NcoI end of the AroA gene from pRPA-BL 104,
recur with EcoRI.
Transit peptide of the SSU of maize RuBisCO/sequence of 22 amino
acids of the mature part of the SSU of maize RuBisCO/AroA gene
fusion:
Similarly, a 228-bp EcoRI-HindII fragment of the cDNA of the SSU of
the maize RuBisCO gene is ligated with the Klenow
polymerase-treated NcoI end of the AroA gene from pRPA-BL 104 and
recur with EcoRI. A translational fusion is obtained between the
transit peptide of the SSU of maize RuBisCO, the 22 amino acids of
the mature part of the SSU of maize RuBisCO and the bacterial EPSPS
gene.
Transit peptide of the SSU of sunflower RuBisCO:
The fragment is derived from the cDNA isolated by Waksman and
Freyssinct (1987). An SphI site was created at the cleavage site of
the transit peptide according to the method of Zoller and Smith
(1984). The transit peptide of the SSU of sunflower RuBisCO thus
obtained is a 171-bp EcoRI-SphI fragment.
Transit peptide of the SSU of sunflower RuBisCO/sequence of 22
amino acids of the mature part of the SSU of maize RuBisCO/AroA
gene fusion:
The construct containing the transit peptide of the SSU of maize
RuBisCO/sequence of 22 amino acids of the SSU of maize RuBisCO of
the mature part of the maize gene fusion was cut with 171-bp
EcoRI-SphI corresponding to the transit peptide of the SSU of
sunflower RuBisCO. A resulting construct exhibits a substitution of
the EcoRI-SphI fragments and is a translational fusion "transit
peptide of the SSU of sunflower RuBisCO/sequence of 22 amino acids
of the mature part of the SSU of maize RuBisCO/AroA gene.
The EcoRI-SalI fragment was ligated with the SalI-SstI fragment
containing the 3' nos sequence and the right end of the T-DNA. The
resulting EcoRI-SstI fragment, comprising "transit peptide of the
SSU of sunflower RuBisCO/sequence of 22 amino acids of the mature
part of the SSU of maize RuBisCO/AroA gene/3' nos/T-DNA fight end",
is substituted for the EcoRI-SstI fragment containing the fight end
of the T-DNA of the plasmid 150 A alpha 2 containing the double
CaMV promoter. The transcriptional fusion "double CaMV/transit
peptide of the SSU of sunflower RuBisCO/sequence of 22 amino acids
of the mature pan of the SSU of maize RuBisCO/AroA gene/3' nos" in
the vector 150 A alpha 2 was called pRPA-BL 294.
"Transit peptide of the SSU of sunflower RuBisCO/sequence of 22
amino acids of the SSU of maize RuBisCO/transit peptide of the SSU
of maize RuBisCO/AroA gene" fusion:
The above construct is cut with NcoI-HindIII, releasing the Area
gene. Next it is ligated with a 1.5 kbp NcoI-HindIII fragment
containing the "transit peptide of the SSU of maize RuBisCO/AroA
gene" fusion. A resulting construct exhibits a substitution of the
NcoI-HindIII fragments and is a translational fusion "transit
peptide of the SSU of sunflower RuBisCO/sequence of 22 amino acids
of the SSU of the RuBisCO of the mature part of the maize
gene/transit peptide of the SSU of maize RuBisCO/AroA gene".
The EcoRI-SalI fragment was ligated with the SalI-SstI fragment
containing the 3' nos sequence and the right end of the T-DNA. The
resulting EcoRI-SstI fragment comprising "transit peptide of the
SSU of sunflower RuBisCO/sequence of 22 amino acids of the SSU of
the RuBisCO of the mature part of the maize gene/transit peptide of
the SSU of maize RuBisCO/AroA gene/3' nos/T-DNA fight end" is
substituted for the EcoRI-SstI fragment containing the right end of
the T-DNA of the plasmid 150 A alpha 2 containing the double CaMV
promoter. The transcriptional fusion "double CaMV/transit peptide
of the SSU of sunflower RuBisCO/sequence of 22 amino acids of the
SSU of the RuBisCO of the mature part of the maize gene/transit
peptide of the SSU of maize RuBisCO/AroA gene/3' nos" in the vector
150 A alpha 2 was called pRPA-BL 410.
EXAMPLE 2: RESISTANCE OF THE TRANSFORMED PLANTS
1. Transformation:
The vector is introduced into the nononcogenic agrobacterium strain
EHA 101 (Hood et al., 1987) carrying the cosmid pTVK 291 (Komari et
al., 1986). The transformation method is based on the procedure of
Horsh et al. (1985).
2. Regeneration:
The regeneration of the tobacco PBD6 (source SEITA France) using
foliar explants is carried out on a Murashige and Skoog (MS) basic
medium containing 30 g/l of sucrose and 200 g/ml of kanamycin. The
foliar explants are removed from greenhouse- or in vitro-grown
plants and transformed according to the foliar disc method (Science
1985, Vol. 227, p. 1229-1231) in three successive stages: the first
comprises the induction of shoots on an MS medium supplemented with
30 g/l of sucrose containing 0.05 mg/l of naphthylacetic acid (ANA)
and 2 mg/l of benzylaminopurine (BAP), for 15 days. The shoots
formed during this stage are then developed by culturing on an MS
medium supplemented with 30 g/l of sucrose, but not containing
hormone, for 10 days. The developed shoots are then removed and
they are cultured on an MS planting medium containing half the
content of salts, vitamins and sugars and not containing hormone.
After about 15 days, the deeply-rooted shoots are placed in
soil.
3. Measurement of the glyphosate tolerance:
a) In vitro: the tolerance is measured by weighing the mass of
calluses extrapolated to 100 foliar discs of 0.5 cm in diameter,
after 30 days of growth on an MS medium supplemented with 30 g/l of
sucrose, 0.05 mg/l of naphthaleneacetic acid and 2 mg/l of BAP
containing 35 ppm of glyphosate and 200 micrograms/ml of kanamycin.
Under these conditions, it is observed that for the tobacco plants
modified by the chimeric gene of pRPA BL 410 according to the
invention, the mass of calluses is 34 g whereas for the plants
modified by the chimeric gene without a second transit peptide, the
mass is only 12 g.
b) In vivo: 30 plants derived from the regeneration of the tobaccos
transformed using pRPA-BL 294 and pRPA-BL 410 respectively are
transferred to a greenhouse and treated at the 5-leaf stage by
spraying with an aqueous suspension at a dose corresponding to 0.6
kg/ha of glyphosate (Round up). After 21 days, a phenotypic
examination is carded out of the plants relative to untransformed
control plants. Under these conditions, it is observed that the
plants transformed using pRPA-BL 410 possess a negligible
phytotoxicity whereas the control plants are completely destroyed;
moreover, the plants transformed using a chimeric gene, which
differs from the preceding one by the absence of a second transit
peptide, possess a phytotoxicity of not less than 30%
destruction.
These results clearly show the improvement brought by the use of a
chimeric gene according to the invention for the same gene encoding
the glyphosate tolerance.
The transformed plants according to the invention may be used as
parents for producing lines and hybrids having an increased
tolerance to glyphosate.
EXAMPLE 3
Spring colzas, Westar cultivar, resistant to glyphosate, were
obtained using the method of BOULTER et al., 1990 (Plant Science,
70:91-99), with pRPA-BL410. These plants were resistant to a
greenhouse treatment with glyphosate at 400 g a.s/ha, a treatment
which destroys nontransgenic plants.
* * * * *