What is claimed is: 1. A plant comprising an expression cassette for reducing gene expression of a plant target gene sequence, comprising: (i) a polynucleotide that shares sequence identity with at least a part of the plant target gene sequence; and (ii) an inverted repeat of the polynucleotide, wherein the polynucleotide and its inverted repeat are positioned in between, and operably linked to, two promoters that are each functional in plants, wherein (a) the polynucleotide and its inverted repeat are fully identical in sequence over at least 23 nucleotides, (b) the direction of transcription is from one promoter toward the other promoter, and (c) neither the polynucleotide nor its inverted repeat is operably linked to a terminator. 2. The plant of claim 1, wherein the polynucleotide of (i) shares sequence identity with at least a part of: a regulatory element, an exon, an intron, a 5'-untranslated region, or a 3'-untranslated region, of an endogenous plant target gene sequence. 3. The plant of claim 2, wherein the endogenous plant target gene sequence is a COMT gene involved in lignin biosynthesis, a CCOMT gene involved in lignin biosynthesis, any other gene involved in lignin biosynthesis, an R1 gene involved in starch phosphorylation, a phosphorylase gene involved in starch phosphorylation, a PPO gene involved in oxidation of polyphenols, a polygalacturonase gene involved in pectin degradation, a gene involved in the production of allergens, or a gene involved in fatty acid biosynthesis. 4. The plant of claim 1, wherein the expression cassette is located between transfer-DNA border sequences of a plasmid that is suitable for bacterium-mediated plant transformation, wherein the bacterium is a strain of Agrobacterium, Rhizobium, or Phyllobacterium. 5. The plant of claim 1, wherein the expression cassette further comprises: a spacer polynucleotide, positioned between the polynucleotide and the inverted repeat of the polynucleotide, wherein the spacer polynucleotide is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 300, 400, 500, or more than 500 nucleotides long. 6. The plant of claim 1, wherein each promoter is selected from the group consisting of: a constitutive promoter, a tissue-specific promoter, or an inducible promoter, and wherein the second promoter is a constitutive promoter, a near-constitutive promoter, a tissue-specific promoter, or an inducible promoter. 7. The plant of claim 1, wherein the expression cassette is stably transformed into the plant genome. 8. The plant of claim 1, wherein at least one of the promoters is specific to a plant tissue selected from the group consisting of: tuber, seed, leaf, root, vascular system, flower, pollen, and ovule. 9. The plant of claim 1, wherein the plant is selected from the group consisting of: potato, tomato, tobacco, avocado, alfalfa, lettuce, carrot, strawberry, sugarbeet, cassava, sweet potato, soybean, pea, bean, cucumber, grape, brassica, maize, turf grass, wheat, rice, barley, sorghum, oat, oak, eucalyptus, walnut, palm, orchid, lily, onion, banana, sugarcane, pepper, broccoli, cotton, poinsettia, legumes, rose, mint, squash, daisy, and cactus. 10. The plant of claim 1, wherein the plant is a potato plant. 11. A potato grown from the plant of claim 10. 12. A food product made from the plant of claim 1, wherein the food product contains the expression cassette. 13. A food product made from the plant of claim 1, wherein the plant is a potato plant, and wherein the food product contains the expression cassette. 14. A food product made from the plant of claim 1, wherein the plant is a potato plant and the food product is made from the tuber of said plant, and wherein the food product contains the expression cassette. 15. A food product made from the plant of claim 1, wherein the plant is a potato plant and the food product is a cut potato, and wherein the food product contains the expression cassette. 16. A food product made from the plant of claim 1, wherein the plant is a potato plant and the food product is a French fry or chip, and wherein the food product contains the expression cassette. 17. A potato comprising an expression cassette for reducing gene expression of a plant target gene sequence, comprising: (i) a polynucleotide that shares sequence identity with at least a part of the plant target gene sequence; and (ii) an inverted repeat of the polynucleotide, wherein the polynucleotide and its inverted repeat are positioned in between, and operably linked to, two promoters that are each functional in plants, wherein (a) the polynucleotide and its inverted repeat are fully identical in sequence over at least 23 nucleotides, (b) the direction of transcription is from one promoter toward the other promoter, and (c) neither the polynucleotide nor its inverted repeat is operably linked to a terminator. 18. A food product made from the potato of claim 17, wherein the food product contains the expression cassette. 19. The food product of claim 18, wherein the food product is a cut potato, and wherein the food product contains the expression cassette. 20. The food product of claim 18, wherein the food product is a French fry or chip, and wherein the food product contains the expression cassette. 21. A method of making a food product, the method comprising: processing a potato comprising an expression cassette, wherein the expression cassette comprises (i) a polynucleotide that shares sequence identity with at least a part of the plant target gene sequence; and (ii) an inverted repeat of the polynucleotide, wherein the polynucleotide and its inverted repeat are positioned in between, and operably linked to, two promoters that are each functional in plants, wherein (a) the polynucleotide and its inverted repeat are fully identical in sequence over at least 23 nucleotides, (b) the direction of transcription is from one promoter toward the other promoter, and (c) neither the polynucleotide nor its inverted repeat is operably linked to a terminator. 22. The method of claim 21, wherein the food product is a French fry or chip. 23. The method of claim 21, wherein processing the potato comprises slicing or cutting the potato. 24. The method of claim 23, wherein processing the potato comprises cutting the potato into wedges. |