Polymorphism in the Barley Granule Bound Starch Synthase 1 (<i>Gbss1</i>) Gene Associated with Grain Starch Variant Amylose Concentration

Abstract

Granule bound starch synthase 1 (GBSS1) accumulation within starch granules and structure of Gbss1 alleles were determined for nine barley ( Hordeum vulgare L.) genotypes producing amylose-free (undetectable), near-waxy (1.6-4.5%), normal (25.8%), and increased (38.0-40.8%) amylose grain starches. Compared to normal starch granules, GBSS1 accumulation was severely reduced in three near-waxy, slightly reduced in two waxy, and slightly elevated in three increased amylose starches. Gbss1 nucleotide sequence analysis for the nine genotypes distinguished them into three Gbss1 groups with several single-nucleotide polymorphisms. A new unique Q312H substitution within GBSS1 was discovered in near-waxy genotype SB94912 with reduced amylose (1.6%) concentration relative to the other two near-waxy lines, CDC Rattan and CDC Candle (4.5%). The two waxy genotype GBSS1 showed a previously described D287V change for CDC Alamo and a new G513W change for CDC Fibar. Both amino acid alterations are conserved residues within starch synthase domains involved in glucan interaction. The increased amylose genotypes showed several unique nucleotide changes within the second and fourth Gbss1 introns, but only SB94893 GBSS1 showed a unique amino acid substitution, A250T in exon 6. The Gbss1 nucleotide differences were used to design genetic markers to monitor Gbss1 alleles in genotypes with various amylose grain starches.