Catalyzes the first step in the synthesis of DIMBOA, forming indole from indole-3-glycerol phosphate. The enzyme is called indole-3-glycerol phosphate lyase, chloroplast, EC 4.1.2.8 and is located in the chloroplast. The X-ray structure of BX1 protein has been resolved and compared with bacterial TSA (tryptophan synthase alpha subunit, Kulik et al. 2005). Three homologs of the BX1 protein occur in maize. One is encoded by the gene tsa1, tryptophan synthase alpha1(Frey et al. 1997, Melanson et al. 1997 ), on chromosome 7, another by igl1, indole-3-glycerol phosphate lyase1(Frey et al. 1997, on chromosome 1, and another by tsah1, TSA like" and located near the bx1'  gene (Frey et al. 1997. ).