Altering lignin and wood density

1. A nucleic acid construct comprising a SAMdc nucleotide sequence and, operably linked thereto, a xylem-preferred promoter.

2. A plant comprising the construct of claim 1 .

3. The plant of claim 2 , wherein said plant is an angiosperm.

4. The plant of claim 2 , wherein said plant is a gymnosperm.

5. A plant or part thereof that overexpresses a nucleotide sequence encoding a SAMdc enzyme, which nucleotide sequence is under the control of a xylem-preferred promoter, such that said plant has reduced lignin levels compared with a control plant.

6. The plant of claim 5 , wherein said plant is an angiosperm.

7. The plant of claim 5 , wherein said plant is a gymnosperm.

8. The plant of claim 5 , wherein said plant is a woody tree.

9. The plant of claim 6 , wherein said woody tree is a Eucalyptus plant.

10. The plant of claim 6 , wherein said woody tree is a Populus plant.

11. The plant of claim 7 , wherein said woody tree is a Pinus plant.

12. A part of the plant of claim 5 , wherein said part is selected from the group consisting of a leaf, a stem, a flower, an ovary, a fruit, a seed, and a callus, wherein said part comprises a SAMdc nucleotide sequence and, operably linked thereto, a xylem-preferred promoter.

13. Progeny of the plant of claim 5 , wherein said progeny comprise a SAMdc nucleotide sequence and, operably linked thereto, a xylem-preferred promoter.

14. A method for decreasing lignin content in a plant, comprising: (a) introducing into a plant cell a nucleic acid construct comprising, in the 5′ to 3′ direction, a xylem-preferred promoter operably linked to a SAMdc nucleotide sequence; (b) regenerating transgenic plants from said plant cell; and (c) selecting a transgenic plant having decreased lignin content relative to a control plant.

15. The method of claim 14 , wherein said plant is an angiosperm.

16. The method of claim 14 , wherein said plant is a gymnosperm.

17. The method of claim 15 , wherein said plant is Eucalyptus or Populus.

18. The method of claim 16 , wherein said plant is Pinus.

19. The method of claim 14 , wherein said nucleic acid is selected from the group consisting of: (a) a nucleotide sequence set forth in any of SEQ ID NO: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 24, and 26; (b) a nucleotide sequence that encodes a polypeptide having the amino acid sequence set forth in any of SEQ ID NO: 2, 4, 6, 8, 10, 12, 14, 16, and 18; (c) a nucleotide sequence that differs from the nucleotide sequences of (a) or (b) due to degeneracy of the genetic code and encodes a polypeptide with SAMdc enzyme activity.

20. A method for increasing the ratio of syringyl lignin to guaiacyl lignin in a woody plant, comprising overexpressing a SAMdc nucleotide sequence with a xylem-preferred promoter.

21. A method for increasing wood density in a plant, comprising (a) introducing into a plant cell a nucleic acid construct comprising, in the 5′ to 3′ direction, a xylem-preferred promoter operably linked to a SAMdc nucleotide sequence; (b) regenerating transgenic plants from said plant cell; and (c) selecting a transgenic plant having reduced vessel area and reduced vessel density relative to a control plant.

22. The method of claim 21 , wherein said plant is an angiosperm.

23. The method of claim 21 , wherein said plant is a gymnosperm.

24. The method of claim 22 , wherein said plant is Eucalyptus or Populus.

25. The method of claim 23 , wherein said plant is Pinus.

26. Wood pulp obtained from a transgenic plant produced by the method of claim 21 , wherein said wood pulp comprises a SAMdc nucleotide sequence and, operably linked thereto, a xylem-preferred promoter.

27. Wood fiber obtained from a transgenic plant produced by the method of claim 21 , wherein said wood fiber comprises a SAMdc nucleotide sequence and, operably linked thereto, a xylem-preferred promoter.

28. A method for increasing wood density and decreasing lignin content in a plant, comprising: (a) introducing into a plant cell a nucleic acid construct comprising, in the 5′ to 3′ direction, a xylem-preferred promoter operably linked to a SAMdc nucleotide sequence; (b) regenerating transgenic plants from said plant cell; and (c) selecting a transgenic plant having increased wood density and decreased lignin content relative to a control plant.

29. The method of claim 28 , wherein said plant is an angiosperm.

30. The method of claim 28 , wherein said plant is a gymnosperm.

31. The method of claim 29 , wherein said plant is Eucalyptus or Populus.

32. The method of claim 30 , wherein said plant is Pinus.

33. A method of making wood pulp, comprising (a) introducing into a plant cell a nucleic acid construct comprising, in the 5′ to 3′ direction, a xylem-preferred promoter operably linked to a SAMdc nucleotide sequence; (b) regenerating transgenic plants from said plant cell; (c) selecting a transgenic plant having increased wood density and decreased lignin content relative to a control plant; and (d) producing wood pulp from said transgenic plant.

34. The method of claim 33 , wherein said xylem-preferred promoter is selected from the group consisting of TUB gene promoter, LTP gene promoter, 4CL gene promoter, and C4H gene promoter.

35. A method of making wood fiber, comprising (a) introducing into a plant cell a nucleic acid construct comprising, in the 5′ to 3′ direction, a xylem-preferred promoter operably linked to a SAMdc nucleotide sequence; (b) regenerating transgenic plants from said plant cell; (c) selecting a transgenic plant having increased wood density and decreased lignin content relative to a control plant; and (d) producing wood fiber from said transgenic plant.