Lycopene ε-cyclase (ε-LCY) is a key enzyme that catalyzes the synthesis of α-branch carotenoids through the cyclization of lycopene. Two cDNA molecules encoding
ε-LCY (designated
Ntε-LCY1 and
Ntε-LCY2) were cloned from
Nicotiana tabacum.
Ntε-LCY1 and
Ntε-LCY2 are encoded by two distinct genes with different evolutionary origins, one originating from the tobacco progenitor,
Nicotiana sylvestris, and the other originating from
Nicotiana tomentosiformis. The two coding regions are 97% identical at the nucleotide level and 95% identical at the amino acid level. Transcripts of
Ntε-LCY were detectable in both vegetative and reproductive organs, with a relatively higher level of expression in leaves than in other tissues. Subcellular localization experiments using an Ntε-LCY1-GFP fusion protein demonstrated that mature Ntε-LCY1 protein is localized within the chloroplast in Bright Yellow 2 suspension cells. Under low-temperature and low-irradiation stress,
Ntε-LCY transcript levels substantially increased relative to control plants. Tobacco rattle virus (TRV)-mediated silencing of
ε-LCY in
Nicotiana benthamiana resulted in an increase of β-branch carotenoids and a reduction in the levels of α-branch carotenoids. Meanwhile, transcripts of related genes in the carotenoid biosynthetic pathway observably increased, with the exception of
β-OHase in the
TRV-ε-lcy line. Suppression of
ε-LCY expression was also found to alleviate photoinhibition of Potosystem II in virus-induced gene silencing (VIGS) plants under low-temperature and low-irradiation stress. Our results provide insight into the regulatory role of
ε-LCY in plant carotenoid biosynthesis and suggest a role for
ε-LCY in positively modulating low temperature stress responses.
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