Institute of Molecular Plant Biology, ETH Zurich, 8092, Zurich, Switzerland.
Laboratory for Biological Geochemistry, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
Nat Commun. 2021 Nov 26;12(1):6944. doi: 10.1038/s41467-021-27151-5.
Living cells orchestrate enzyme activities to produce myriads of biopolymers but cell-biological understanding of such processes is scarce. Starch, a plant biopolymer forming discrete, semi-crystalline granules within plastids, plays a central role in glucose storage, which is fundamental to life. Combining complementary imaging techniques and Arabidopsis genetics we reveal that, in chloroplasts, multiple starch granules initiate in stromal pockets between thylakoid membranes. These initials coalesce, then grow anisotropically to form lenticular granules. The major starch polymer, amylopectin, is synthesized at the granule surface, while the minor amylose component is deposited internally. The non-enzymatic domain of STARCH SYNTHASE 4, which controls the protein's localization, is required for anisotropic growth. These results present us with a conceptual framework for understanding the biosynthesis of this key nutrient.
活细胞通过协调酶的活性来产生无数的生物聚合物，但对这些过程的细胞生物学理解还很匮乏。淀粉是一种植物生物聚合物，在质体中形成离散的半结晶颗粒，在葡萄糖储存中起着核心作用，而葡萄糖储存对生命是至关重要的。通过结合互补的成像技术和拟南芥遗传学，我们揭示了在叶绿体中，多个淀粉颗粒首先在类囊体膜之间的基质小囊中形成。这些初始颗粒融合在一起，然后以各向异性的方式生长，形成透镜状颗粒。主要的淀粉聚合物支链淀粉在颗粒表面合成，而较小的直链淀粉成分则在内部沉积。控制蛋白质定位的淀粉合成酶 4 的非酶结构域对于各向异性生长是必需的。这些结果为我们理解这种关键营养物质的生物合成提供了一个概念框架。
