Abstract
Carotenoids are important pigments in plants that play crucial roles in plant growth and in plant responses to environmental stress. Lycopene β cyclase (β-LCY) functions at the branch point of the carotenoid biosynthesis pathway, catalyzing the cyclization of lycopene. Here, a β-LCY gene from Nicotiana tabacum, designated as Ntβ-LCY1, was cloned and functionally characterized. Robust expression of Ntβ-LCY1 was found in leaves, and Ntβ-LCY1 expression was obviously induced by salt, drought, and exogenous abscisic acid treatments. Strong accumulation of carotenoids and expression of carotenoid biosynthesis genes resulted from Ntβ-LCY1 overexpression. Additionally, compared to wild-type plants, transgenic plants with overexpression showed enhanced tolerance to salt and drought stress with higher abscisic acid levels and lower levels of malondialdehyde and reactive oxygen species. Conversely, transgenic RNA interference plants had a clear albino phenotype in leaves, and some plants did not survive beyond the early developmental stages. The suppression of Ntβ-LCY1 expression led to lower expression levels of genes in the carotenoid biosynthesis pathway and to reduced accumulation of carotenoids, chlorophyll, and abscisic acid. These results indicate that Ntβ-LCY1 is not only a likely cyclization enzyme involved in carotenoid accumulation but also confers salt and drought stress tolerance in Nicotiana tabacum.
Highlights
Due to the ever increasing severity of environmental deterioration, both water scarcity and soil salinization have become major problems in agriculture that limit plant growth and cause serious economic losses [1]
We found that two copies of β-LCY showed the highest transcript levels in the lower leaf maturity stage, the transcript levels of most of the genes in the carotenoid biosynthetic pathway showed a declining trend from the flowering stage to lower leaf maturity stage, which suggested that the β-LCY gene might play an important role in the accumulation of carotenoids in mature tobacco leaves
We found two β-LCY genes in the RNA sequencing results; these were designated as Ntβ-LCY1 and Ntβ-LCY2
Summary
Due to the ever increasing severity of environmental deterioration, both water scarcity and soil salinization have become major problems in agriculture that limit plant growth and cause serious economic losses [1]. Lutein accumulation is reduced or completely absent in the lut and lut mutants of Arabidopsis, owing to the lack of functional copies of the ε-carotene hydroxylase (ε-OHase) and lycopene ε-cyclase (ε-LCY) genes, respectively. These mutants had increased accumulation of β-branch carotenoid compounds [29,30]. Chen et al found that overexpression of the β-LCY gene in transgenic Arabidopsis enhanced plant tolerance to oxidative stress and salt stress [32]; these findings motivated us to investigate the function of Ntβ-LCY in carotenoid accumulation and in plant responses to drought and salt stress in tobacco. Our results suggest that Ntβ-LCY1 plays an important role in carotenoid accumulation and tolerance to abiotic stress, and indicate that Ntβ-LCY1 may prove useful in potential applications for molecular breeding and/or biotechnology in plants
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