Wheat mutants lacking Starch Synthase 1 have altered starch composition and cell wall content

Abstract Starch Synthase 1 (SS1) participates in the synthesis of amylopectin. To determine its role in hexaploid bread wheat, we selected and combined TILLING mutations for each homoeologue to create two independent SS1-deficient lines. The lines, which have different combinations of ss1 mutations, both lacked SS1 protein. Both lines exhibited mild but significant changes to starch phenotype, including fewer short amylopectin chains, a slight increase in B-type starch granules and a modest increase in amylose content. Lack of SS1 also led to changes in the thermal properties of starch measured by differential scanning calorimetry including reduced enthalpy, and increased gelatinization temperature. Despite the changes to starch properties, the starch contents of the mutant lines compared to wild types were within the normal range, as were grain weight and protein content. However, the concentration of total- and water-extractable arabinoxylan, and MLG, were increased in white flour compared to wild-type controls. Highlight Lack of SS1 led to changes in starch molecular structure and thermal behavior. Starch content and grain weight were normal but cell wall polysaccharides in white flour were increased. Competing Interest Statement The authors have declared no competing interest. Footnotes E-mail addresses: Error! Hyperlink reference not valid. Brendan.Fahy{at}jic.ac.uk Oscar.Gonzalez{at}ragt.com Marianna.Pasquariello{at}crea.gov.it Jennifer.Ahn-Jarvis{at}quadram.ac.uk Judith.Mayne{at}quadram.ac.uk Ondrej.Kosik{at}rothamsted.ac.uk Alison.Lovegrove{at}rothamsted.ac.uk Fred.Warren{at}quadram.ac.uk Brittany.Hazard{at}jic.ac.uk Abbreviations - DP - Degree of polymerization - DSC - Differential scanning calorimetry - HPLC - High performance liquid chromatography - FWT - Fresh weight - DWT - Dry weight - SEC - Size exclusion chromatography - SEM - Scanning electron microscopy - TILLING - Targeting induced local lesions in genomes - AX - Arabinoxylan - TO-AX - Total AX - WE-AX - Water-extractable AX - AXOS AX - oligosaccharides - MLG - Mixed linkage glucan (β-glucan) - MLGOS - MLG oligosaccharides - WT - Wild type (AABBDD) - MUT - Mutant (aabbdd) - NIR - Near-infrared