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bioRxiv · 10.64898/2026.04.27.721068

A cyclo-DOPA 6-O-glucosyltransferase-mediated route for gomphrenin I biosynthesis in Basella alba and Gomphrena globosa

Imamura, T.·Shigehisa, R.·Miyazato, A.·Matsumura, N.·Miyaki, K.·Segawa, T.·Yoshizumi, M.·Takagi, H.·Yamaguchi, T.·Ohki, S.·Mori, M.
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Abstract

O_LIBetacyanins are red pigments characteristic of Caryophyllales and show considerable structural diversity, yet the enzymatic basis underlying 6-O-glucosylated betacyanins such as gomphrenin I has remained unclear. In particular, how alternative glucosylation patterns contribute to betacyanin diversification is poorly understood. C_LIO_LIHere, we identified cyclo-DOPA glucosyltransferases from Basella alba and Gomphrena globosa and examined their roles in gomphrenin I biosynthesis using transient expression assays and tobacco BY-2 cell systems. Phylogenetic analyses, structural modelling and site-directed mutagenesis were employed to investigate their functional and structural characteristics. C_LIO_LIBacDOPA5/6GTs catalysed both 5-O- and 6-O-glucosylation of cyclo-DOPA, leading to the production of betanin and gomphrenin I, whereas GgcDOPA6GT specifically mediated gomphrenin I formation. These enzymes belong to distinct subclades within the cDOPA-GT family, and mutational analyses demonstrated essential roles for conserved histidine residues and an -helical region adjacent to the catalytic site. C_LIO_LIThermal stability analyses further showed that gomphrenin I is more thermally stable than betanin, likely due to the formation of an intramolecular hydrogen bond. Together, these results reveal an additional cDOPA6GT-mediated route for gomphrenin I biosynthesis and provide insight into the diversification and functional specialization of betacyanins, linking the position of glucosylation to pigment stability and biochemical properties. C_LI

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Imamura, T., Shigehisa, R., Miyazato, A., Matsumura, N., Miyaki, K., Segawa, T., Yoshizumi, M., Takagi, H., Yamaguchi, T., Ohki, S., Mori, M.. 2026-04-30. A cyclo-DOPA 6-O-glucosyltransferase-mediated route for gomphrenin I biosynthesis in Basella alba and Gomphrena globosa. https://doi.org/10.64898/2026.04.27.721068

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