Waxy and non-waxy barley cultivars exhibit differences in the targeting and catalytic activity of GBSS1a

Kim Hebelstrup, Morten Munch Nielsen, Massimiliano Carciofi, Olga Andrzejczak, Shahnoor Sultana Shaik, Andreas Blennow, Monica M Palcic

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Amylose synthesis is strictly associated with activity of granule-bound starch synthase (GBSS) enzymes. Among several crops there are cultivars containing starch types with either little or no amylose known as near-waxy or waxy. This (near) amylose-free phenotype is associated with a single locus (waxy) which has been mapped to GBSS-type genes in different crops. Most waxy varieties are a result of either low or no expression of a GBSS gene. However, there are some waxy cultivars where the GBSS enzymes are expressed normally. For these types, single nucleotide polymorphisms have been hypothesized to represent amino-acid substitutions leading to loss of catalytic activity. We here confirm that the HvGBSSIa enzyme from one such waxy barley variety, CDC_Alamo, has a 90% reduction in catalytic activity. We also engineered plants with expression of transgenic C-terminal green fluorescent protein-tagged HvGBSSIa of both the non-waxy type and of the CDC_Alamo type to monitor their subcellular localization patterns in grain endosperm. HvGBSSIa from non-waxy cultivars was found to localize in discrete concentric spheres strictly within starch granules. In contrast, HvGBSSIa from waxy CDC_Alamo showed deficient starch targeting mostly into unknown subcellular bodies of 0.5–3 µm in size, indicating that the waxy phenotype of CDC_Alamo is associated with deficient targeting of HvGBSSIa into starch granules.
Original languageEnglish
JournalJournal of Experimental Botany
Pages (from-to)931-941
Number of pages11
Publication statusPublished - 11 Feb 2017


  • Amylose
  • GBSS
  • starch biosynthesis
  • starch functionality
  • subcellular targeting
  • waxy


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