Strigolactone biosynthesis catalyzed by cytochrome P450 and sulfotransferase in sorghum

Abstract

Root parasitic plants such as 𝘚𝘵𝘳𝘪𝘨𝘢, 𝘖𝘳𝘰𝘣𝘢𝘯𝘤𝘩𝘦, and 𝘗𝘩𝘦𝘭𝘪𝘱𝘢𝘯𝘤𝘩𝘦 spp. cause serious damage to crop production world-wide. Deletion of the 𝘓𝘰𝘸 𝘎𝘦𝘳𝘮𝘪𝘯𝘢𝘵𝘪𝘰𝘯 𝘚𝘵𝘪𝘮𝘶𝘭𝘢𝘯𝘵 1 (𝘓𝘎𝘚1) gene gives a 𝘚𝘵𝘳𝘪𝘨𝘢-resistance trait in sorghum (𝘚𝘰𝘳𝘨𝘩𝘶𝘮 𝘣𝘪𝘤𝘰𝘭𝘰𝘳). The 𝘓𝘎𝘚1 gene encodes a sulfotransferase-like protein, but its function has not been elucidated.

Since the profile of strigolactones (SLs) that induce seed germination in root parasitic plants is altered in the 𝘭𝘨𝘴1 mutant, LGS1 is thought to be an SL biosynthetic enzyme. In order to clarify the enzymatic function of LGS1, we looked for candidate SL substrates that accumulate in the lgs1 mutants and performed 𝘪𝘯 𝘷𝘪𝘷𝘰 and 𝘪𝘯 𝘷𝘪𝘵𝘳𝘰 metabolism experiments.

We found the SL precursor 18-hydroxycarlactonoic acid (18-OH-CLA) is a substrate for LGS1. CYP711A cytochrome P450 enzymes (SbMAX1 proteins) in sorghum produce 18-OH-CLA. When 𝘓𝘎𝘚1 and 𝘚𝘣𝘔𝘈𝘟1 coding sequences were co-expressed in Nicotiana benthamiana with the upstream SL biosynthesis genes from sorghum, the canonical SLs 5-deoxystrigol and 4-deoxyorobanchol were produced.

This finding showed that LGS1 in sorghum uses a sulfo group to catalyze leaving of a hydroxyl group and cyclization of 18-OH-CLA. A similar SL biosynthetic pathway has not been found in other plant species.