Abstract
Carotenoids, chlorophylls and gibberellins are derived from the common precursor geranylgeranyl diphosphate (GGPP). One of the enzymes in carotenoid biosynthesis is lycopene β-cyclase (LCYB) that catalyzes the conversion of lycopene into β-carotene. In carrot, Dclcyb1 is essential for carotenoid synthesis in the whole plant. Here we show that when expressed in tobacco, increments in total carotenoids, β-carotene and chlorophyll levels occur. Furthermore, photosynthetic efficiency is enhanced in transgenic lines. Interestingly, and contrary to previous observations where overexpression of a carotenogenic gene resulted in the inhibition of the synthesis of gibberellins, we found raised levels of active GA4 and the concommitant increases in plant height, leaf size and whole plant biomass, as well as an early flowering phenotype. Moreover, a significant increase in the expression of the key carotenogenic genes, Ntpsy1, Ntpsy2 and Ntlcyb, as well as those involved in the synthesis of chlorophyll (Ntchl), gibberellin (Ntga20ox, Ntcps and Ntks) and isoprenoid precursors (Ntdxs2 and Ntggpps) was observed. These results indicate that the expression of Dclcyb1 induces a positive feedback affecting the expression of isoprenoid gene precursors and genes involved in carotenoid, gibberellin and chlorophyll pathways leading to an enhancement in fitness measured as biomass, photosynthetic efficiency and carotenoid/chlorophyll composition.
Highlights
Carotenoids are the most widespread group of pigments et al, 2004; Takaichi, 2011)
These results indicate that the expression of Dclcyb1 induces a positive feedback affecting the expression of isoprenoid gene precursors and genes involved in carotenoid, gibberellin and chlorophyll pathways leading to an enhancement in fitness measured as biomass, photosynthetic efficiency and carotenoid/chlorophyll composition
Considering that Dclcyb gene product is involved in the formation of β-carotene and lutein (Fig. 1), the increase in these carotenoids is expected, and indicates that Dclcyb1 promotes the synthesis of pigments of both branches
Summary
Carotenoids are the most widespread group of pigments et al, 2004; Takaichi, 2011). In general, carotenoids have high found in nature. Carotenoids is β-carotene, which serves, along with α-carotene, as a dietary precursor of vitamin A, which is required for the maintenance of normal vision, cell growth and for healthy immunity, among other physiological processes (Olson, 1996). In plants, these compounds are synthesized in plastids where they play essential roles in light absorption during photosynthesis, photo-protection via energy dissipation, and detoxification of reactive oxygen species (ROS). Carotenoids synthesized and stored in chromoplasts provide yellow, orange and red colors to fruits and flowers for animalmediated pollination and seed dispersal
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