Novel starch types : molecular diversity for future applications

This thesis investigated molecular changes in potato starch achieved through targeted mutations in the starch synthesis pathway. CRISPR/Cas9 was used to induce mutations in starch branching enzyme genes (SBE), with or without mutations in granule bound starch synthase gene (GBSS). The resulting starch was characterised for molecular and functional attributes. Barley starch obtained through conventional cross-breeding was also characterised, to explore potential impacts of fructan synthesis changes on starch synthesis at composition and molecular structure level. Inducing mutations in all alleles of the SBEI and some alleles of the SBEII produced high-amylose starch, while inducing mutations in all alleles of both SBEs resulted in amylose-only starch. GBSS mutations alone yielded a waxy starch phenotype, while introducing GBSS mutations in SBEs mutated background led to non-waxy, low-amylose lines. Mutations in SBEI produced starch with unit chain distributions close to the native variety. Mutations in the GBSS produced starch with building blocks (BB) distribution resembling the native variety. Significant deviations to unit chain and BB distribution were observed when both SBEI and SBEII were mutated. Presence of high proportions of large BB elevated gelatinisation and retrogradation temperatures, while high proportions of short amylopectin chains lowered gelatinisation temperature. Potato lines with diverse genetic backgrounds exhibited variations in pasting profiles, influencing film-forming behaviour. Natural genetic variation-based conventional cross-breeding of barley produced starch with modified structures, as upregulated fructan synthesis resulted in starch with a high proportion of large BB. These novel insights into how alterations in starch synthesis pathway affect starch properties pave the way for tailored starch development.