Condensed tannins (CT) are flavonoids that share large part of their biosynthetic pathway with anthocyanins. CTs occur in a wide range of plants where play important role in defence against herbivores and pathogens and have important industrial applications. As food components, they act as antioxidants with beneficial effects for human and animal health (Dixon et al. 2005). In animal feeding they exert a positive or negative effect depending on the amount: large amounts (>10mg/g of DM) confer a bitter taste to forages and prevent the free intake by the animals, converselymoderate amounts (2-5 mg/g of DM) in legume forages increase protein assimilation by the animal. For their capacity of interact with proteins CTs in fact prevent bloating in ruminants (Tanner, 2004). The major forage legumes accumulate these products in seed coat and not in leaves. The goal of the research in this field is thus to engineer CT biosynthesis in leaves of forage legumes to produce bloat-safe varieties. Investigating and manipulating the regulatory apparatus seems therefore a promising strategy. In Arabidopsis the MYB, bHLH and WD40 (MBW) complex controls CT and anthocyanin pigmentation as well as the development of trichomes and root hairs. Within this complex, the WD component is common to all the different functional complexes, while the bHLH and MYB proteins are flexible and the specifity in regulating the different pathways in different tissues is conferred by different MYBs (Zhang et al. 2003). In forage legumes, the ectopic expression of bHLH and/or WD genes did not result in de novo synthesis of CT in vegetative tissues (Paolocci et al. 2007). All in all, MYBs appear to be the best candidate to finely switch on and off the CT pathway not only in Arabidopsis but in forage species as well. Here we report on the effects of the ectopic expression of VvMYBPA1, a Vitis vinifera R2R3MYB that specifically activates the structural genes of CT pathway (Bogs et al., 2007), in the model species Nicotiana tabacum. Transgenic 35S:MYBPA1 tobacco lines were assayed for flower colour and showed phenotypes with high degree of variability ranging from pink (wt) to white. Flower colour resulted negatively correlated to CT accumulation suggesting that VvMYBPA1 redirects anthocyanin synthesis toward CT. Molecular and metabolic analyses will elucidate whether VvMYBPA1 prevents anthocyanin formation by channelling all the common precursors toward CT biosynthesis. Transformation of Medicago truncatula and M.sativa is in progress to test the possibility to divert the flux from the anthocyanidin pathway to CTs to produce bloat-safe forage legumes.
VvMYBPA1 diverts the flux from the anthocyanidin pathway to condensed tannins in tobacco flowers
Damiani F;Paolocci F
2009
Abstract
Condensed tannins (CT) are flavonoids that share large part of their biosynthetic pathway with anthocyanins. CTs occur in a wide range of plants where play important role in defence against herbivores and pathogens and have important industrial applications. As food components, they act as antioxidants with beneficial effects for human and animal health (Dixon et al. 2005). In animal feeding they exert a positive or negative effect depending on the amount: large amounts (>10mg/g of DM) confer a bitter taste to forages and prevent the free intake by the animals, converselymoderate amounts (2-5 mg/g of DM) in legume forages increase protein assimilation by the animal. For their capacity of interact with proteins CTs in fact prevent bloating in ruminants (Tanner, 2004). The major forage legumes accumulate these products in seed coat and not in leaves. The goal of the research in this field is thus to engineer CT biosynthesis in leaves of forage legumes to produce bloat-safe varieties. Investigating and manipulating the regulatory apparatus seems therefore a promising strategy. In Arabidopsis the MYB, bHLH and WD40 (MBW) complex controls CT and anthocyanin pigmentation as well as the development of trichomes and root hairs. Within this complex, the WD component is common to all the different functional complexes, while the bHLH and MYB proteins are flexible and the specifity in regulating the different pathways in different tissues is conferred by different MYBs (Zhang et al. 2003). In forage legumes, the ectopic expression of bHLH and/or WD genes did not result in de novo synthesis of CT in vegetative tissues (Paolocci et al. 2007). All in all, MYBs appear to be the best candidate to finely switch on and off the CT pathway not only in Arabidopsis but in forage species as well. Here we report on the effects of the ectopic expression of VvMYBPA1, a Vitis vinifera R2R3MYB that specifically activates the structural genes of CT pathway (Bogs et al., 2007), in the model species Nicotiana tabacum. Transgenic 35S:MYBPA1 tobacco lines were assayed for flower colour and showed phenotypes with high degree of variability ranging from pink (wt) to white. Flower colour resulted negatively correlated to CT accumulation suggesting that VvMYBPA1 redirects anthocyanin synthesis toward CT. Molecular and metabolic analyses will elucidate whether VvMYBPA1 prevents anthocyanin formation by channelling all the common precursors toward CT biosynthesis. Transformation of Medicago truncatula and M.sativa is in progress to test the possibility to divert the flux from the anthocyanidin pathway to CTs to produce bloat-safe forage legumes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
