The biosynthesis of DIMBOA, a pesticidal secondary metabolite of maize, branches off the tryptophan pathway. We have previously demonstrated that indole is the last intermediate common to both the tryptophan and hydroxamic acid pathways. The earliest discovered mutant in the DIMBOA pathway, bxbx (benzoxazineless), is deficient in the production of DIMBOA and related compounds. This paper presents evidence We demonstrate that the TSA gene has sustained a 924-bp deletion in bxbx compared with its counterpart in wild-type maize. We report that the TSA gene maps to the same location as the bxbx mutation, on the short arm of chromosome 4. We present evidence that the very early and very high level of expression of TSA corresponds to the timing and level of DIMBOA biosynthesis but is strikingly different from the expression of the maize tryptophan synthase  (TSB) genes. We show that feeding indole to bxbx seedlings restores their ability to synthesize DIMBOA. We conclude that the maize enzyme initially named tryptophan synthase ␣ in fact is a DIMBOA biosynthetic enzyme, and we propose that it be renamed indole synthase. This work confirms and enlarges upon the findings of Frey et al.
Protoplast-derived, transformed maize plants were evaluated by Southern analysis for the presence of the aph IV gene which codes for resistance to the antibiotic, hygromycin B. This gene was used as a selectable marker for the transformation of maize protoplasts. Southern analysis was performed with fluorescein-labeled probe DNA. A new method for labeling molecular weight markers with fluorescein-N 6 is presented. The nonradioactive Southern analysis method is compared to the radioactive method and the results show that the nonradioactive method is as sensitive as the radioactive method.
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