Elucidation of the β‐carotene hydroxylation pathway in Arabidopsis thaliana

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Abstract
The first dedicated step in plant xanthophyll biosynthesis is carotenoid hydroxylation. In Arabidopsis thaliana, this reaction is performed by both heme (LUT1 and LUT5) and non-heme (CHY1 and CHY2) hydroxylases. No mutant completely abolishing α- or β-carotene hydroxylation has been described to date. We constructed double and triple mutant combinations in CHY1, CHY2, LUT1, LUT5 and LUT2 (lycopene epsilon-cyclase). In chy1chy2lut2, 80% of leaf carotenoids is represented by β-carotene. In chy1chy2lut5, β-carotene hydroxylation is completely abolished, while hydroxylation of the β-ring of α-carotene is still observed. The data are consistent with a role of LUT5 in β-ring hydroxylation, and with the existence of an additional hydroxylase, acting on the β-ring of α-, but not β-carotene