Overexpression of petunia chalcone isomerase in tomato results in fruit containing increased levels of flavonols

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 ( approximately 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.

Changes in Transcriptional Profiles Are Associated with Early Fruit Tissue Specialization in Tomato

“…Many of these genes (up to 36% in the locular tissue) encode proteins with unknown functions or, alternatively, present no homology with known genes. Our findings correlate well for the few genes or enzymatic activities previously studied in the developing fruit (Laval-Martin et al, 1977;Schaffer and Petreikov, 1997;Rebers et al, 1999;RodriguezConception and Gruissem, 1999;Joubès et al, 2000;Lemaire-Chamley et al, 2000;Muir et al, 2001;Guillet et al, 2002;Busi et al, 2003;Obiadalla-ali et al, 2004). Interestingly, the repartition of the known genes into the different functional categories is very different between the exocarp and the locular tissue.…”

“…Other exocarp-expressed proteins can be involved in fruit defense against pathogens (glucanase and chitinase) or in stress tolerance (UV radiation and heat). These include key enzymes required for the synthesis of flavonoids (Phe ammonia-lyase, flavanone hydroxylase, and flavonol synthase; Muir et al, 2001) and of ascorbic acid (GDP Man pyrophosphorylase; Smirnoff …”

“…Since most of the studies to date have focused on the entire fruit or on the carpel wall, how the different fruit tissues contribute to fruit growth and affect fruit quality remains poorly understood. There are nevertheless some indications of early tissue specialization in the fruit, since structural and biochemical changes such as cell size (Mohr and Stein, 1969;Gillaspy et al, 1993), endoreduplication level (Joubès et al, 1999), photosynthesis (Laval-Martin et al, 1977;Meier et al, 1995), starch accumulation (Schaffer and Petreikov, 1997), cell wall polysaccharides (Cheng and Huber, 1996), and flavonoid composition (Muir et al, 2001) show great variation among the different fruit tissues. These data suggest coordinated expressions of genes with specific roles in the control of growth and regional differentiation in the various tissues of the developing fruit.…”

RNA Interference Silencing of Chalcone Synthase, the First Step in the Flavonoid Biosynthesis Pathway, Leads to Parthenocarpic Tomato Fruits

“…The main flavonoids accumulating in wild-type tomato fruits are naringenin (NAR)-chalcone and the flavonol rutin (quercetin-3-rutinoside). In fruits, these flavonoids are predominantly produced in the peel because the flavonoid pathway is inactive in flesh tissue (Muir et al, 2001;Bovy et al, 2002). In peel extracts of Chs RNAi fruits, a large decrease was observed in the levels of both rutin and NAR-chalcone when compared with extracts from control plants (Fig.…”

“…The more intense red color of Chs RNAi fruits was most probably due to the reduction in the levels of the yellow-pigmented NAR-chalcone normally present at high levels in epidermal cells of the ripening fruit (Hunt and Baker, 1980). Interestingly, chalcone isomeraseoverexpressing fruits display reduced NAR-chalcone levels, a more intense red color, and a dull appearance as well (Muir et al, 2001). This suggests a relationship between flavonoids and fruit dullness.…”