Development and validation of breeder-friendly functional markers of sugary1 gene encoding starch-debranching enzyme affecting kernel sweetness in maize (Zea mays)

The sweet corn variety of maize (Zea mays L.) has become popular worldwide. The recessive allele of sugary1 (su1) encoding starch de-branching enzyme has been much used for sweet corn cultivar development. Here, we aimed to develop su1-based functional marker(s) by using six diverse inbred lines of sugary type and five inbred lines of wild type, and using 27 overlapping primers. In total, 12 indels (insertion and deletion) and 96 SNPs (single nucleotide polymorphisms) were identified that clearly differentiated the dominant and recessive allele of su1. Among these, a 36-bp indel (at position 1247) in the promoter region included a TATA-box, and a 6-bp indel (at position 6456) in intron-10 was predicted to have SRp40 exon-splicing enhancer. Nucleotide substitution in exon-2 at position 2703 (SNP-2703) was involved in C to G mutation leading to conversion of phenylalanine to leucine. The 6-bp and 36-bp indels and SNP-2703 were used to develop breeder-friendly codominant markers: SuDel6-FR, SuDel36-FR and SNP2703-CG-85/89. All three markers were validated in five F2 populations, and SuDel36-FR and SNP2703-CG-85/89 were validated in a set of 230 diverse inbreds having both mutant and wild-type alleles of Su1. This is the first report of development and validation of universal functional markers for su1. These markers (SuDel36-FR and SNP2703-CG-85/89) assume great significance in marker-assisted breeding program.