Characterization of bread wheat starch mutants by transcriptome analyses targeted to grain metabolic pathways

Reserve starch, the major component of wheat kernel, consists of amylose and amylopectin. The variation in their ratio (about 1:3 in normal wheat) has a potential impact on the nutritional and technological properties of wheat-derived foods. Previously, three complete null lines of key starch biosynthesis genes (granule-bound starch synthase I, GBSSI; starch synthase IIa, SSIIa; starch branching enzyme IIa, SBEIIa) were generated in bread wheat and named Cad-GBSSI*, Cad-SSIIa*, and Cad-SBEIIa*, respectively (Botticella et al., 2018). The lines expressed novel kernel traits, including reduction in amylose content (by 100%, 54%, and 21%, respectively) and modification of resistant starch content, amylopectin/amylose ratio, seed hardness, and appearance. To refine the characterisation of starch metabolism and to bring out divergences underlying pleiotropic effects, morpho-anatomical and omics analyses were performed on Cad-GBSSI*, Cad-SSIIa* and Cad-SBEIIa* mutant kernels sampled at 25 days post anthesis and the results were compared to the wild type.

储备淀粉是小麦籽粒的主要组成成分，由直链淀粉（amylose）与支链淀粉（amylopectin）构成。二者的比例（普通小麦中约为1:3）的变化，会对小麦源食品的营养特性与加工品质产生潜在影响。此前，研究人员在普通小麦（bread wheat）中成功构建了3个关键淀粉生物合成基因的完全功能缺失纯合系，分别为颗粒结合型淀粉合成酶I（granule-bound starch synthase I, GBSSI）、淀粉合成酶IIa（starch synthase IIa, SSIIa）与淀粉分支酶IIa（starch branching enzyme IIa, SBEIIa）的敲除系，并将其分别命名为Cad-GBSSI*、Cad-SSIIa*与Cad-SBEIIa*（Botticella等，2018）。这些突变系展现出全新的籽粒性状：直链淀粉含量分别降低100%、54%与21%，同时抗性淀粉（resistant starch）含量、支链淀粉/直链淀粉比例、籽粒硬度与外观均发生改变。为进一步解析淀粉代谢过程，并阐明多效性效应背后的分子差异，研究人员对开花后25天采集的Cad-GBSSI*、Cad-SSIIa*与Cad-SBEIIa*突变籽粒开展了形态解剖学与多组学（omics）分析，并将结果与野生型对照进行对比。