Genes encoding sulfate assimilation proteins

Details Genes encoding sulfate assimilation proteins Genes encoding sulfate assimilation proteins

2003-03-03

2004-11-23

Saidha, Tekchand (Department: 1652)

Chemistry: molecular biology and microbiology

Enzyme , proenzyme; compositions thereof; process for...

Transferase other than ribonuclease

C435S252300, C435S320100, C435S471000, C536S023200, C530S350000

Reexamination Certificate

active

06821764

ABSTRACT:

FIELD OF THE INVENTION
This invention is in the field of plant molecular biology. More specifically, this invention pertains to nucleic acid fragments encoding sulfate assimilation proteins in plants and seeds.
BACKGROUND OF THE INVENTION
Sulfate assimilation is the process by which environmental sulfur is fixed into organic sulfur for use in cellular metabolism. The two major end products of this process are the essential amino acids cysteine and methionine. These amino acids are limiting in food and feed; they cannot be synthesized by animals and thus must be acquired from plant sources. Increasing the level of these amino acids in feed products is thus of major economic value. Key to that process is increasing the level of organic sulfur available for cysteine and methionine biosynthesis.
Multiple enzymes are involved in sulfur assimilation. These include: High affinity sulfate transporter and low affinity sulfate transporter proteins which serve to transport sulfur from the outside environment across the cell membrane into the cell (Smith et al. (1995)
PNAS
92(20):9373-9377). Once sulfur is in the cell sulfate adenylyltransferase (ATP sulfurylase) (Bolchia et al. (1999)
Plant Mol. Biol.
39(3):527-537) catalyzes the first step in assimilation, converting the inorganic sulfur into an organic form, adenosine-5′ phosphosulfate (APS). Next, several enzymes further modify organic sulfur for use in the biosynthesis of cysteine and methionine. For example, adenylylsulfate kinase (APS kinase), catalyzes the conversion of APS to the biosynthetic intermediate PAPS (3′-phosphoadenosine-5′ phosphosulfate) (Arz et al. (1994)
Biochim. Biophy. Acta
1218(3):447-452). APS reductase (5′ adenylyl phosphosulphate reductase) is utilized in an alternative pathway, resulting in an inorganic but cellularly bound (bound to a carrier), form of sulfur (sulfite) (Setya et al. (1996)
PNAS
93(23):13383-13388). Sulfite reductase further reduces the sulfite, still attached to the carrier, to sulfide and serine O-acetyltransferase converts serine to O-acetylserine, which will serve as the backbone to which the sulfide will be transferred to from the carrier to form cysteine (Yonelcura-Sakakibara et al. (1998)
J. Biolchem.
124(3):615-621 and Saito et al. (1995)
J. Biol. Chem.
270(27):16321-16326).
As described, each of these enzymes is involved in sulfate assimilation and the pathway leading to cysteine biosynthesis, which in turn serves as an organic sulfur donor for multiple other pathways in the cell, including methionine biosynthesis. Together or singly these enzymes and the genes that encode them have utility in overcoming the sulfur limitations known to exist in crop plants. It may be possible to modulate the level of sulfur containing compounds in the cell, including the nutritionally critical amino acids cysteine and methionine. Specifically, their overexpression using tissue specific promoters will remove the enzyme in question as a possible limiting step, thus increasing the potential flux through the pathway to the essential amino acids. This will allow the engineering of plant tissues with increases levels of these amino acids, which now often must be added a supplements to animal feed.
SUMMARY OF THE INVENTION
The instant invention relates to isolated nucleic acid fragments encoding sulfate assimilation proteins. Specifically, this invention concerns an isolated nucleic acid fragment encoding a serine O-acetyltransferase and an isolated nucleic acid fragment that is substantially similar to an isolated nucleic acid fragment encoding a serine O-acetyltransferase. In addition, this invention relates to a nucleic acid fragment that is complementary to the nucleic acid fragment encoding serine O-acetyltransferase. An additional embodiment of the instant invention pertains to a polypeptide encoding all or a substantial portion of a serine O-acetyltransferase.
In another embodiment, the instant invention relates to a chimeric gene encoding a serine O-acetyltransferase, or to a chimeric gene that comprises a nucleic acid fragment that is complementary to a nucleic acid fragment encoding a serine O-acetyltransferase, operably linked to suitable regulatory sequences, wherein expression of the chimeric gene results in production of levels of the encoded protein in a transformed host cell that is altered (i.e., increased or decreased) from the level produced in an untransformed host cell.
In a further embodiment, the instant invention concerns a transformed host cell comprising in its genome a chimeric gene encoding a serine O-acetyltransferase, operably linked to suitable regulatory sequences. Expression of the chimeric gene results in production of altered levels of the encoded protein in the transformed host cell. The transformed host cell can be of eukaryotic or prokaryotic origin, and include cells derived from higher plants and microorganisms. The invention also includes transformed plants that arise from transformed host cells of higher plants, and seeds derived from such transformed plants.
An additional embodiment of the instant invention concerns a method of altering the level of expression of a serine O-acetyltransferase in a transformed host cell comprising: a) transforming a host cell with a chimeric gene comprising a nucleic acid fragment encoding a serine O-acetyltransferase; and b) growing the transformed host cell under conditions that are suitable for expression of the chimeric gene wherein expression of the chimeric gene results in production of altered levels of serine O-acetyltransferase in the transformed host cell.
An addition embodiment of the instant invention concerns a method for obtaining a nucleic acid fragment encoding all or a substantial portion of an amino acid sequence encoding a serine O-acetyltransferase.


REFERENCES:
Frank W. Smith et al., Plant Members of a Family of Sulfate Transporters Reveal Functional Subtypes, PNAS, vol. 92:9373-9377, Sep. 1995.
Angelo Bolchi et al., Coordinate Modulation of Maize Sulfate Permease and ATP Sulfurylase mRNAs In Response to Variations in Sulfur Nutritional Status: Stereospecific Down-Regulation by L-Cysteine, Plant Molecular Biology, vol. 39:527-537, 1999.
Hildegard E. Arz et al., A cDNA for Adenylyl Sulphate (APS)-kinase fromArabidopsis thallana, Biochimica et Biophysica Acta, vol. 1218:447-452, 1994.
Amit Setya et al., Sulfate Reduction in Higher Plants: Molecular Evidence for a Novel 5′-adenylylsulfate Reductase, PNAS, vol. 93:13383-13388, Nov. 1996.
Keiko Yonekura-Sakakibara et al., Molecular Characterization of Tobacco Sulflte Reductase: Enzyme Purification, Gene Cloning, and Gene Expression Analysis, J. Biochem., vol. 124:615-621, 1998.
Kazuki Saito et al., Molecular Cloning and Characterization of a Plant Serine Acetyltransferase Playing a Regulatory Role in Cysteine Biosynthesis from Watermelon,J. Biol. Chem., vol. 270(27):16321-16326, 1995.
National Center for Biotechnology Information General Indentifier No. 1361979, Jul. 20, 2000, Saito, K. et al., Molecular Cloning and Characterization of a Plant Serine Acetyltransferase Playing a Regulatory Role in Cysteine Biosynthesis from Watermelon.
National Center for Biotechnology Information General Indentifier No. 2146774, May 5, 2000, Howarth, J. R. et al.
National Center for Biotechnology Information General Indentifier No. 1107505, Mar. 19, 1996, Hell, R. et al., A cDNA Encoding Serine Acetyltransferase fromArabidopsis thaliana.
Michael A. Roberts et al., Cloning and characterisation of anArabidopsis thalianacDNA clone encoding an organellar isoform of serine acetyltranferase, Plant Molecular Biology, vol. 30:1041-1049, 1996.
EMBL Database Accession No: C26373.1, Aug. 6, 1997, T. Sasaki et al., Rice DNA from Callus (970724).
EMBL Database Accession No: P93544, May 1, 1997, K. Saito et al.
B. Yoo et al., Regulation of recombinant soybean serine acetyltransferase by CDPK, Plant Phys. Suppl., vol. 114:267, 1997, XP002128629.
K. Saito et al., Molecular Characterization of cysteine biosynthetic enzymes in plants, Comptes Rendus De L&apos

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