Down-regulation of gene expression using artificial MicroRNAs for silencing fatty acid biosynthetic genes

1. An isolated polynucleotide comprising a sequence encoding at least one artificial microRNA precursor, operably linked to at least one regulatory polynucleotide, wherein upon transcription of the sequence a transcript comprising the artificial miRNA precursor is produced, wherein processing of the transcript excises a mature miRNA about 21 to 22 nucleotides in length from the artificial miRNA precursor, the mature miRNA inhibiting expression of fad3, and wherein the at least one artificial microRNA precursor comprises SEQ ID NO: 130.

2. A recombinant construct comprising the isolated polynucleotide of claim 1 operably linked to at least one heterologous regulatory sequence.

3. A plant cell comprising the recombinant construct of claim 2 .

4. The plant cell of claim 3 wherein the plant cell is a dicot plant cell.

5. A method for reducing expression at least one plant fatty acid biosynthetic gene, the method comprising transforming a plant cell with at least one isolated nucleic acid sequence comprising a sequence encoding at least one artificial microRNA precursor, operably linked to at least one regulatory sequence, wherein:

(a) the at least one sequence encoding an artificial microRNA precursor is transcribed to produce a transcript comprising the at least one artificial miRNA precursor;

(b) the transcript is processed so that at least one mature miRNA about 21 to 22 nts in length is excised from the artificial miRNA precursor; and

(c) expression of fad3 is reduced;

and wherein the at least one artificial microRNA precursor comprises SEQ ID NO:130.

6. The method of claim 5 wherein the plant cell is a dicot plant cell.

7. An isolated polynucleotide comprising a sequence encoding two or more artificial microRNA precursors, operably linked to at least one regulatory polynucleotide, the two or more artificial microRNA precursors being on the same or separate transcriptional units, wherein upon transcription of the sequence a transcript comprising the artificial miRNA precursors is produced, and wherein processing of the transcript excises mature miRNAs about 21 to 22 nucleotides in length from the artificial miRNA precursors, the mature miRNAs inhibiting expression of fad3 and at least one fad2 delta-12 desaturase, wherein at least one of said two or more artificial microRNA precursors comprises SEQ ID NO:130.

8. A recombinant construct comprising the isolated polynucleotide of claim 7 operably linked to at least one heterologous regulatory sequence.

9. A plant cell comprising the recombinant construct of claim 8 .

10. The plant cell of claim 9 wherein the plant cell is a dicot plant cell.

11. A method for reducing expression of two or more plant fatty acid biosynthetic genes, the method comprising transforming a plant cell with at least one isolated polynucleotide comprising a sequence encoding two or more artificial microRNA precursors, the two or more artificial microRNA precursors being on the same or separate transcriptional units and operably linked to at least one regulatory sequence wherein:

(a) the at least one sequence encoding two or more artificial microRNA precursors is transcribed to produce at least one transcript comprising the two or more artificial miRNA precursors;

(b) the at least one transcript is processed so that at least two different mature miRNAs about 21 to 22 nucleotides in length are excised from the artificial miRNA precursors; and

(c) expression of fad3 and at least one fad2 delta-12 desaturase gene are reduced,

and wherein at least one of said two or more artificial microRNA precursors comprises SEQ ID NO:130.

12. The method of claim 11 wherein the plant cell is a dicot plant cell.

13. An isolated polynucleotide comprising a sequence encoding at least one artificial microRNA precursor, operably linked to at least one regulatory polynucleotide, wherein the sequence encoding at least one artificial microRNA precursor is capable of forming a double-stranded RNA or hairpin, wherein the at least one artificial microRNA precursor comprises an miRNA sequence and its corresponding complementary STAR sequence, and wherein excision of the miRNA sequence from the artificial microRNA precursor inhibits expression of fad3, and further wherein the at least one artificial microRNA precursor comprises a nucleotide sequence as set forth in SEQ ID NO:130.

14. An isolated polynucleotide comprising a sequence encoding two or more artificial microRNA precursors, operably linked to at least one regulatory polynucleotide, the two or more artificial microRNA precursors being on the same or separate transcriptional units, wherein the sequences encoding two or more artificial microRNA precursors are capable of forming a double-stranded RNA or hairpin, wherein the two or more artificial microRNA precursors comprise two or more miRNA sequences and their corresponding complementary STAR sequences, wherein excision of the miRNA sequences from the two or more artificial microRNA precursors inhibits expression of fad3 and at least one fad2 delta-12 desaturase, and wherein at least one of the two or more artificial microRNA precursors comprises SEQ ID NO:130.

15. The isolated polynucleotide of claim 14 , wherein at least one of the two or more miRNA sequences comprises SEQ ID NO: 24.

16. A transgenic plant or seed comprising the polynucleotide of claim 1 , 13 or 14 .

17. The method according to claim 5 , wherein the miRNA sequence comprises SEQ ID NO: 24.

18. The isolated polynucleotide of claim 14 , wherein at least one of the two or more amiRNA sequences comprises SEQ ID NO: 24 and another one comprises SEQ ID NO: 21 or 22.

19. The method according to claim 11 , wherein at least one of said two or more amiRNA sequences comprises SEQ ID NO: 24 and another one comprises SEQ ID NO: 21.

20. The method according to claim 11 , wherein at least one of said two or more amiRNA sequences comprises SEQ ID NO: 24 and another one comprises SEQ ID NO: 22.