John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK.
Harper Adams University, Newport TF10 8NB, UK.
Plant Physiol. 2024 Nov 4;196(3):1980-1996. doi: 10.1093/plphys/kiae429.
Molecular factors that contribute to the diverse spatial and temporal patterns of starch granule initiation between species and organs are poorly understood. Wheat (Triticum sp.) endosperm contains both large A-type granules initiated during early grain development and small B-type granules that initiate about 10 to 15 days later. Here, we identify that the MYOSIN-RESEMBLING CHLOROPLAST PROTEIN (MRC) is required for the correct timing of B-type granule initiation in wheat endosperm during grain development. MRC is expressed in the endosperm exclusively in early grain development, before B-type granule initiation. We isolated three independent TILLING mutants of tetraploid wheat (Triticum turgidum cv. 'Kronos') with premature stop or missense mutations in the A-genome homeolog, which we showed to be the only active homeolog in tetraploid wheat due to a disruption of the B-genome homeolog. The mrc mutants had significantly smaller A-type granules and a higher relative volume of B-type granules in the endosperm than the wild type. Whereas B-type granules initiated 15 to 20 days post-anthesis (dpa) in the wild type, they appeared as early as 10 dpa in the mrc-1 mutant. These results suggest a temporal role for MRC in repressing B-type granule initiation, providing insight into how the distinct biochemical mechanisms that control A- and B-type granule initiation are regulated. This role of MRC in the wheat endosperm is distinct from the previously described role of Arabidopsis (Arabidopsis thaliana) MRC in promoting granule initiation in leaves, providing an example of functional diversification among granule initiation proteins.
分子因素导致物种和器官之间淀粉颗粒起始的空间和时间模式多样化，但目前对此知之甚少。小麦（Triticum sp.）胚乳中既有在谷物早期发育过程中起始的大型 A 型颗粒，也有大约在 10 到 15 天后起始的小型 B 型颗粒。在这里，我们发现肌球蛋白类似叶绿体质体蛋白（MRC）对于小麦胚乳中 B 型颗粒在谷物发育过程中的正确起始时间是必需的。MRC 在胚乳中的表达仅限于早期谷物发育阶段，即在 B 型颗粒起始之前。我们分离了三个独立的四倍体小麦（Triticum turgidum cv. 'Kronos'） TILLING 突变体，它们在 A 基因组同源基因中具有过早终止或错义突变，我们证明由于 B 基因组同源基因的破坏，该基因是四倍体小麦中唯一活跃的同源基因。mrc 突变体的胚乳中 A 型颗粒明显较小，B 型颗粒的相对体积较高。而在野生型中，B 型颗粒在授粉后 15 到 20 天（dpa）开始出现，而在 mrc-1 突变体中，它们早在 10 dpa 就出现了。这些结果表明 MRC 在抑制 B 型颗粒起始方面具有时间作用，为了解控制 A 型和 B 型颗粒起始的不同生化机制如何受到调节提供了线索。MRC 在小麦胚乳中的作用与先前描述的拟南芥（Arabidopsis thaliana）MRC 在促进叶片中颗粒起始的作用不同，为颗粒起始蛋白的功能多样化提供了一个例子。
