Benzoxazinoid biosynthesis - Zea mays (maize)
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Benzoxazinoids (hydroxamic acids) are plant secondary metabolites that serve as important factors for host resistance against microbial pathogens and insects and for allelopathic effects. They are found in grass family and some eudicot families. The predominant benzoxazinoids are DIBOA and its 7-methoxy derivative DIMBOA, which are stored as glucosides in vacuoles. In maize, benzoxazinoid biosynthesis branches off from tryptophan biosynthesis at indole-3-glycerol phosphate, which is converted to indole by indole-3-glycerol phosphate lyase, BX1. Subsequently four cytochrome P450 monooxygenases (BX2-BX5) catalyze the introduction of four oxygen atoms into the indole moiety, yielding DIBOA. After glucosylation by UDP-glucosyltransferase (BX8/BX9), the glucoside is further modified by hydroxylation and O-methylation at C-7 to form DIMBOA-glucoside.