Genetically modified tomato

Abstract: Tomatoes are an excellent source of the carotenoid lycopene, a compound that is thought to be protective against prostate cancer. They also contain small amounts of flavonoids in their peel (∼5–10 mg/kg fresh weight), mainly naringenin chalcone and the flavonol rutin, a quercetin glycoside. Flavonols are very potent antioxidants, and an increasing body of epidemiological data suggests that high flavonoid intake is correlated with a decreased risk for cardiovascular disease. We have upregulated flavonol biosynthesis in the tomato in order to generate fruit with increased antioxidant capacity and a wider range of potential health benefit properties. This involved transformation of tomato with the Petunia chi-a gene encoding chalcone isomerase. Resulting transgenic tomato lines produced an increase of up to 78 fold in fruit peel flavonols, mainly due to an accumulation of rutin. No gross phenotypical differences were observed between high-flavonol transgenic and control lines. The phenotype segregated with the transgene and demonstrated a stable inheritance pattern over four subsequent generations tested thus far. Whole-fruit flavonol levels in the best of these lines are similar to those found in onions, a crop with naturally high levels of flavonol compounds. Processing of high-flavonol tomatoes demonstrated that 65% of flavonols present in the fresh fruit were retained in the processed paste, supporting their potential as raw materials for tomato-based functional food products.

Abstract: The structure of an insect control protein gene from Bacillus thuringiensis var. kurstaki HD–1 was determined, and truncated forms of the gene that express a functional insecticidal protein were generated. Two of these truncated genes were incorporated into a plant expression vector for Agrobacterium–mediated transformation. Transgenic tomato plants containing the chimeric genes express the insect control protein gene. Such expression confers tolerance to lepidopteran larvae on the transgenic tomato plants and their progeny. These engineered tomato plants represent a significant step to increased selectivity, specificity and efficiency in insect control.

Abstract: Polyphenol oxidases (PPOs; EC 1.10.3.2 or EC 1.14.18.1) catalyzing the oxygen-dependent oxidation of phenols to quinones are ubiquitous among angiosperms and assumed to be involved in plant defense against pests and pathogens. In order to investigate the role of PPO in plant disease resistance, we made transgenic tomato (Lycopersiconesculentum Mill. cv. Money Maker) plants that overexpressed a potato (Solanumtuberosum L.) PPO cDNA under control of the cauliflower mosaic virus 35S promoter. The transgenic plants expressed up to 30-fold increases in PPO transcripts and 5- to 10-fold increases in PPO activity and immunodetectable PPO. As expected, these PPO-overexpressing transgenic plants oxidized the endogenous phenolic substrate pool at a higher rate than control plants. Three independent transgenic lines were selected to assess their interaction with the bacterial pathogen Pseudomonassyringae pv. tomato. The PPO-overexpressing tomato plants exhibited a great increase in resistance to P.syringae. Compared with control plants, these transgenic lines showed less severity of disease symptoms, with over 15-fold fewer lesions, and strong inhibition of bacterial growth, with over 100-fold reduction of bacterial population in the infected leaves. These results demonstrate the importance of PPO-mediated phenolic oxidation in restricting plant disease development.

Abstract: We generated transgenic tomato plants with altered expression of heat stress transcription factor HsfA1. Plants with 10-fold overexpression of HsfA1 (OE plants) were characterized by a single HsfA1 transgene cassette, whereas plants harboring a tandem inverted repeat of the cassette showed cosuppression (CS plants) by posttranscriptional silencing of the HsfA1 gene connected with formation of small interfering RNAs. Under normal growth conditions, major developmental parameters were similar for wild-type (WT), OE, and CS plants. However, CS plants and fruits were extremely sensitive to elevated temperatures, because heat stress-induced synthesis of chaperones and Hsfs was strongly reduced or lacking. Despite the complexity of the plant Hsf family with at least 17 members in tomato, HsfA1 has a unique function as master regulator for induced thermotolerance. Using transient reporter assays with mesophyll protoplasts from WT tomato, we demonstrated that plasmid-encoded HsfA1 and HsfA2 were well expressed. However, in CS protoplasts the cosuppression phenomenon was faithfully reproduced. Only transformation with HsfA2 expression plasmid led to normal expression of the transcription factor and reporter gene activation, whereas even high amounts of HsfA1 expression plasmids were silenced. Thermotolerance in CS protoplasts was restored by plasmid-borne HsfA2, resulting in expression of chaperones, thermoprotection of firefly luciferase, and assembly of heat stress granules.