Molecular Cloning and Characterization of the Granule-Bound Starch Synthesis Gene GBSSI in Andean and Mexican Quinoas

Molecular cloning and Sanger sequencing were used to identify and characterize the starch synthesis gene granule-bound starch synthase I (GBSSI or waxy) in both Chenopodium quinoa and C. berlandieri nutalliae (2n=4x=36, AABB). This gene is responsible for synthesis of one of the two primary forms of seed starch, amylose, as well characterized waxy null mutants in a number of other species (i.e., rice, maize, and quinoa’s cousin amaranth) have starch composed entirely of water-soluble amylopectin. Homeologous sequences from the A and B genomes were identified by comparing GBSSI sequences obtained from wild Chenopodium diploids (AA and BB). Of the A-genome diploids sequenced, C. standleyanum shared the highest percent identity with A-genome copies of tetraploid GBSSI. Eurasian C. ficifolium shared the highest percent identity with B-genome copies. This suggests that C. standleyanum and C. ficifolium may have been the A and B genome donors, respectively. Waxy-phenotype mutants have been identified in three populations of C. berlandieri nuttaliae – the Mexican vegetable crop known as ‘huauzontle’ – and the sequences of their GBSSI null alleles are characterized.