University of Missouri
One mutant rescues another: orange pericarp restores DIMBOA production to bx
In maize, indole is a precursor to the antifeeding compound DIMBOA. The indole is produced from a modified TrpA protein (indole synthase). The bx (benzoxazinineless) phenotype is due to mutation in the indole synthase gene, although DIMBOA can be produced in bx seedlings from exogenous indole (Melanson et al., Proc. Natl. Acad. Sci. USA 94:13345–13350, 1997).
Since the orange pericarp (orp1, orp2) mutant accumulates indole due to mutation in the tryptophan synthase B subunit (Wright et al., Plant Cell 4:711–719, 1992), it might be reasonable to expect DIMBOA to be produced in bx, orp1, orp2 seedlings. To test this possibility I obtained from an F2 family (segragating for orange pericarp and bx) a self-pollination that was homozygous bx and segregating orange pericarp. Ten-day old coleoptiles from bx that were also orange pericarp showed a positive blue color reaction to 5% methanolic ferric chloride. This color reaction was nearly as intense as non-mutant, although it was absent in bx which were not orange pericarp. This finding is consistent with previous work demonstrating indole as a precursor to DIMBOA.