Fahy Brendan, Chen Jiawen, Seung David
John Innes Centre, Norwich Research Park, Norwich, NR4 7UH, UK.
Theor Appl Genet. 2025 Aug 25;138(9):227. doi: 10.1007/s00122-025-05013-8.
Different missense mutations in TtMRC-A1 can be used to fine-tune granule size distributions in durum wheat grains, creating useful alterations in starch properties. The size distribution of starch granules in wheat grains influences bread- and pasta-making quality, as well as nutritional properties. Here, we demonstrate that in durum wheat, wide variation in starch granule size distributions can be induced through missense mutations at a single genetic locus encoding the MYOSIN RESEMBLING CHLOROPLAST PROTEIN on chromosome 6A (TtMRC-A1). We isolated 29 independent TILLING mutants in durum cultivar Kronos, each harbouring a different missense mutation that causes an amino acid substitution in the MRC protein. Compared to the B-type granule content of wild-type Kronos (24%), six of the missense lines had significant increases in B-type granule content (33-42%), although not to the extent observed in the mrc-1 mutant (58%) which carries a premature stop codon mutation. Notably, one missense line had significantly decreased B-type granule content (15%), demonstrating that mutations in TtMRC-A1 can achieve both increases and decreases in B-type granule content. In these lines, A-type granule size decreased as B-type granule content increased, and Rapid Visco Analysis on selected lines demonstrated that both B-type granule content and A-type granule size strongly correlated with pasting parameters (e.g. peak viscosity and pasting temperature). However, strong correlations between pasting properties and A-type granule size were still observed after removing most of the B-type granules via sieving, indicating that A-type granule size is the primary contributor to the observed variation in pasting properties. Overall, we demonstrate that mutations at TtMRC-A1 can greatly extend the range of granule size distributions in durum wheat, creating useful alterations in starch properties.
TtMRC-A1基因中的不同错义突变可用于微调硬粒小麦籽粒中颗粒大小分布，从而对淀粉特性产生有益改变。小麦籽粒中淀粉颗粒的大小分布会影响面包和意大利面的制作品质以及营养特性。在此，我们证明，在硬粒小麦中，通过位于6A染色体上编码类肌球蛋白叶绿体蛋白（TtMRC-A1）的单个基因座处的错义突变，可诱导淀粉颗粒大小分布产生广泛变异。我们在硬粒小麦品种Kronos中分离出29个独立的定向诱导基因组局部突变体（TILLING突变体），每个突变体都带有不同的错义突变，这些突变会导致MRC蛋白中的氨基酸替换。与野生型Kronos的B型颗粒含量（24%）相比，六个错义突变系的B型颗粒含量显著增加（33%-42%），尽管增幅未达到携带提前终止密码子突变的mrc-1突变体（58%）的水平。值得注意的是，一个错义突变系的B型颗粒含量显著降低（15%），这表明TtMRC-A1中的突变既能使B型颗粒含量增加，也能使其降低。在这些品系中，随着B型颗粒含量增加，A型颗粒大小减小，对选定品系进行的快速粘度分析表明，B型颗粒含量和A型颗粒大小均与糊化参数（如峰值粘度和糊化温度）密切相关。然而，通过筛分去除大部分B型颗粒后，仍观察到糊化特性与A型颗粒大小之间存在强相关性，这表明A型颗粒大小是观察到的糊化特性变异的主要贡献因素。总体而言，我们证明TtMRC-A1处的突变可极大地扩展硬粒小麦颗粒大小分布的范围，从而对淀粉特性产生有益改变。
