Increasing leaf longevity and disease resistance by altering salicylic acid catabolism

1. A transgenic plant having a reduced level of salicylic acid 3-hydroxylase (“S3H”), compared to that of a non-transgenic plant, wherein the transgenic plant displays a precocious or premature leaf senescence phenotype, relative to a non-transgenic plant, wherein the plant is transformed with a nucleic acid construct comprising a nucleic acid molecule configured to silence expression of an S3H protein having the amino acid sequence of SEQ ID NO: 3.

2. The plant according to claim 1 , wherein the plant is selected from the group consisting of rice, corn, soybean, canola, potato, wheat, mung bean, alfalfa, barley, rye, cotton, sunflower, peanut, sweet potato, bean, pea, chicory, lettuce, endive, cabbage, brussel sprout, beet, parsnip, turnip, cauliflower, broccoli, radish, spinach, onion, garlic, eggplant, pepper, celery, carrot, squash, pumpkin, zucchini, cucumber, apple, pear, melon, citrus, strawberry, grape, raspberry, pineapple, tobacco, tomato, sorghum , sugarcane, banana, Arabidopsis thaliana, Saintpaulia, petunia, pelargonium , poinsettia, chrysanthemum , carnation, crocus , marigold, daffodil, pine, Medicago truncatula, Sandersonia aurantiaca, Populus trichocarpa , and zinnia.

3. Seed produced from the plant according to claim 1 , wherein the seed comprises the nucleic acid construct.

4. A transgenic plant having an increased level of S3H, compared to that of a non-transgenic plant, wherein said transgenic plant displays a delayed leaf senescence phenotype, relative to a non-transgenic plant, wherein the plant is transformed with a nucleic acid construct that encodes an S3H protein having the amino acid sequence of SEQ ID NO: 3.

5. The plant according to claim 4 , wherein the plant is selected from the group consisting of rice, corn, soybean, canola, potato, wheat, mung bean, alfalfa, barley, rye, cotton, sunflower, peanut, sweet potato, bean, pea, chicory, lettuce, endive, cabbage, brussel sprout, beet, parsnip, turnip, cauliflower, broccoli, radish, spinach, onion, garlic, eggplant, pepper, celery, carrot, squash, pumpkin, zucchini, cucumber, apple, pear, melon, citrus, strawberry, grape, raspberry, pineapple, tobacco, tomato, sorghum , sugarcane, banana, Arabidopsis thaliana, Saintpaulia, petunia, pelargonium , poinsettia, chrysanthemum , carnation, crocus , marigold, daffodil, pine, Medicago truncatula, Sandersonia aurantiaca, Populus trichocarpa , and zinnia.

6. Seed produced from the plant according to claim 4 , wherein the seed comprises the nucleic acid construct.

7. A mutant plant comprising an inactivated gene encoding an S3H protein having the amino acid sequence of SEQ ID NO:3, wherein the mutant plant displays a premature or precocious leaf senescence phenotype, relative to a non-mutant plant.

8. A method for promoting premature or precocious leaf senescence in a plant, said method comprising:

providing a transgenic plant or plant seed transformed with a nucleic acid construct effective in silencing expression of an S3H protein having the amino acid sequence of SEQ ID NO:3 and

growing the transgenic plant or the plant grown from the transgenic plant seed under conditions effective to promote premature or precocious leaf senescence in the transgenic plant or the plant grown from the transgenic plant seed.

9. The method according to claim 8 , wherein said nucleic acid construct comprises:

a nucleic acid molecule configured to silence the S3H protein expression;

a 5′ DNA promoter sequence; and

a 3′ terminator sequence, wherein the nucleic acid molecule, the promoter, and the terminator are operatively coupled to permit expression of the nucleic acid molecule.

10. A method for delaying leaf senescence in a plant, said method comprising:

transforming a plant cell with a nucleic acid molecule encoding an S3H protein comprising the amino acid sequence of SEQ ID NO: 3, wherein the nucleic acid molecule is operably associated with a promoter to obtain a transformed plant cell, wherein expression of the nucleic acid molecule in the plant cell causes delayed leaf senescence; and

regenerating a plant from the transformed plant cell under conditions effective to delay leaf senescence in the plant.

11. The method according to claim 10 , wherein said transforming comprises transforming the plant cell with a nucleic acid construct comprising:

the nucleic acid molecule;

a 5′ heterologous DNA promoter sequence; and

a 3′ terminator sequence, wherein the nucleic acid molecule, the DNA promoter sequence, and the terminator sequence are operatively coupled to permit transcription of the nucleic acid molecule.

12. A method of making a mutant plant having a decreased level of S3H protein compared to that of a non-mutant plant, wherein the mutant plant displays a premature or precocious leaf senescence phenotype relative to a non-mutant plant, said method comprising:

providing at least one cell of a non-mutant plant containing a gene encoding a functional S3H protein comprising the amino acid sequence of SEQ ID NO:3;

treating said at least one cell of a non-mutant plant under conditions effective to inactivate said gene, thereby yielding at least one mutant plant cell containing an inactivated S3H protein encoding gene; and

propagating said at least one mutant plant cell into a mutant plant, wherein said mutant plant has a decreased level of S3H protein compared to that of the non-mutant plant and displays a premature or precocious leaf senescence phenotype relative to a non-mutant plant.

13. A method of inducing or promoting pathogen resistance in plants, said method comprising:

providing a transgenic plant or plant seed transformed with a nucleic acid construct effective in silencing expression of an S3H protein comprising the amino acid sequence of SEQ ID NO:3; and

growing the transgenic plant or the plant grown from the transgenic plant seed under conditions effective to induce or promote pathogen resistance in the transgenic plant or the plant grown from the transgenic plant seed.