5-Deoxystrigol Biosynthesis is a pathway that has not yet become fully elucidated. Beginning in the chloroplast and potentially finishing in the cytosol, the pathway follows the synthesis of 5-deoxystrigol from beta-carotene. 5-Deoxystrigol is a strigolactone, a plant hormone that stimulates the branching and growth of symbiotic arbuscular mycorrhizal fungi and inhibits plant shoot branching. Strigolactones share a common C19 structure composed of a tricyclic lactone (A, B, and C rings) connected to a second lactone (D ring) by an enol ether bridge. 5-deoxystrigol is the precursor of other beta-oriented C-ring strigolactones (strigol-configured strigolactones) (PMID: 25425668). First, beta-carotene isomerase catalyzes the conversion of beta-carotene into 9-cis-beta-carotene with the help of an iron cofactor. Second, 9-cis-beta-carotene 9',10'-cleavage dioxygenase converts 9-cis-beta-carotene and oxygen to 9-cis-10'-apo-beta-carotenal and beta-ionone with the help of an Fe2+ cofactor. Third, carlactone synthase converts 9-cis-10'-apo-beta-carotenal and oxygen to carlactone and (2E,4E,6E)-7-hydroxy-4-methylhepta-2,4,6-trienal with the help of an Fe2+ cofactor. The final two reactions are not completely understood and may occur in the cytosol. Cytochrome P450 monooxygenase is theorized to catalyze the fourth reaction whereby carlactone is conveted into carlactone carboxylate. It requires heme as a cofactor. This same enzyme could possibly also catalyze the fifth reaction in which 5-deoxystrigol is made.

5-Deoxystrigol Biosynthesis References