Method of expressing small peptides using cereal non-storage proteins as fusion carrier in endosperm and the use thereof

1. A method of expressing a small peptide in host endosperm cells, comprising the steps of:

(i) providing an endosperm-specific promoter and a DNA leading sequence encoding an endosperm-specific signal peptide;

(ii) providing a polynucleotide encoding a peptide consisting of a C terminus end of protein disulfide bond dismutase (PDI) as fusion carrier, wherein said C-terminus end possesses molecular chaperone activity;

(iii) providing a target nucleic acid encoding the small peptide, wherein the small peptide is between 20 and 100 amino acids in length;

(iv) constructing an expression vector comprising the promoter, the DNA leading sequence, the polynucleotide encoding the fusion carrier and the target nucleic acid encoding the small peptide wherein the target nucleic acid encoding the small peptide is fused to the 3′ end of the polynucleotide encoding the fusion carrier, wherein a fusion protein expressed from said expression vector comprises the small peptide fused to the C-terminus of said fusion carrier;

(v) transforming a plant cell with the expression vector; and

(vi) regenerating a mature plant from the transformed cell, such that seeds comprising endosperm cells are produced in which the peptide is expressed.

2. The method of claim 1 , further comprising the step of optimizing at least one of DNA leading sequence, the polynucleotide encoding the fusion carrier, and the target nucleic acid encoding the small peptide such that the coding sequence comprises codons preferred by the host, before the step of constructing the expression vector.

3. The method of claim 1 , further comprising the step of introducing a selectable marker into the expression vector.

4. The method of claim 1 , wherein the endosperm-specific promoter and DNA leading sequence are from Gt13a gene; the host is rice, wheat or barley; the C terminus of PDI is from rice, wheat or barley; and the target nucleic acid encoding the small peptide is DNA encoding a therapeutic peptide.

5. The method of claim 4 , wherein the host is rice and the therapeutic peptide is human IGF-1.

6. The method of claim 4 , wherein the host is barley and the therapeutic peptide is human IGF-1.

7. The method of claim 1 , wherein the C terminus of PDI from rice, wheat, or barley comprises an amino acid sequence encoded by the nucleotide sequence of SEQ ID NO: 4.

8. A method of expressing IGF-1 peptide in host endosperm cells, comprising the steps of:

(i) providing an endosperm-specific promoter and a DNA leading sequence encoding an endosperm-specific signal peptide;

(ii) providing a polynucleotide encoding the C terminus end of protein disulfide bond dismutase (PDI) as fusion carrier, wherein said C-terminus end of PDI possesses molecular chaperone activity;

(iii) providing a nucleic acid encoding IGF-1;

(iv) constructing an expression vector comprising the promoter, the DNA leading sequence, the polynucleotide encoding the C-terminus end of PDI and the nucleic acid encoding IGF-1, wherein the nucleic acid encoding IGF-1 is fused to the 3′ end of the polynucleotide encoding PDI, wherein a fusion protein expressed from said expression vector comprises IGF-1 peptide fused to the C-terminus of PDI;

(v) transforming a plant cell with the expression vector; and

(vi) regenerating a mature plant from the transformed cell, such that seeds comprising endosperm cells are produced in which the peptide is expressed.

9. The method of claim 8 , wherein the polynucleotide encoding the C-terminus end of PDI is SEQ ID NO: 4.