Subfunctionalization of D27 Isomerase Genes in Saffron.

Chromoplasts and chloroplasts contain carotenoid pigments as all-- and -isomers, which function as accessory light-harvesting pigments, antioxidant and photoprotective agents, and precursors of signaling molecules and plant hormones. The carotenoid pathway involves the participation of different carotenoid isomerases. Among them, D27 is a β-carotene isomerase showing high specificity for the C9-C10 double bond catalyzing the interconversion of all-- into 9--β-carotene, the precursor of strigolactones. We have identified one () and two ( and ) genes in saffron, with and , clearly differing in their expression patterns; specifically, was mainly expressed in the undeveloped stigma and roots, where it is induced by colonization. On the contrary, and were mainly expressed in leaves, with a preferential expression of in this tissue. In vivo assays show that CsD27-1 catalyzes the isomerization of all-- to 9--β-carotene, and could be involved in the isomerization of zeaxanthin, while CsD27-3 catalyzes the isomerization of all-- to -ζ-carotene and all-- to -neurosporene. Our data show that CsD27-1 and CsD27-3 enzymes are both involved in carotenoid isomerization, with CsD27-1 being specific to chromoplast/amyloplast-containing tissue, and CsD27-3 more specific to chloroplast-containing tissues. Additionally, we show that is co-expressed with and mycorrhized roots, whereas is expressed at higher levels than and and showed circadian regulation in leaves. Overall, our data extend the knowledge about carotenoid isomerization and their implications in several physiological and ecological processes.