A shady business in Legumes: Lutein epoxidase enables α-xanthophyll cycling

Leaves rapidly adjust their xanthophyll pool in response to changes in light to funnel absorbed excitation energy toward either photochemistry or photoprotective energy dissipation. In roughly 60% of species surveyed, α-xanthophylls are interconverted between photoprotective lutein (L) and shade-enriched lutein epoxide (Lx), forming the lutein epoxide cycle (LxL cycle). Despite its prevalence, the enzyme involved in the epoxidation reaction of the LxL cycle is unknown. Using pigment profiling and canopy-specific RNAseq, we detect Lx throughout the middle and lower canopy of soybean and link its accumulation to the expression of a mono-oxygenase we call lutein epoxidase (LEP). We confirm LEP activity in a transient assay in Nicotiana benthamiana. LEPs are distinct from zeaxanthin epoxidases (ZEPs) and are conserved across many legumes. The discovery of an enzyme involved in α-xanthophyll cycling in an agriculturally important crop presents us with a new target for optimizing plant productivity in the shade.