Univ. Lille, CNRS, UMR 8576 - UGSF - Unité de Glycobiologie Structurale et Fonctionnelle, F-59000, Lille, France.
Univ. Lille, CNRS, Inserm, CHU Lille, Institut Pasteur de Lille, US 41 - UAR 2014 - PLBS, F-59000, Lille, France.
New Phytol. 2023 Jul;239(1):132-145. doi: 10.1111/nph.18923. Epub 2023 Apr 19.
The control of starch granule initiation in plant leaves is a complex process that requires active enzymes like Starch Synthase 4 and 3 (SS4 or SS3) and several noncatalytic proteins such as Protein Involved in starch Initiation 1 (PII1). In Arabidopsis leaves, SS4 is the main enzyme that control starch granule initiation, but in its absence, SS3 partly fulfills this function. How these proteins collectively act to control the initiation of starch granules remains elusive. PII1 and SS4 physically interact, and PII1 is required for SS4 to be fully active. However, Arabidopsis mutants lacking SS4 or PII1 still accumulate starch granules. Combining pii1 KO mutation with either ss3 or ss4 KO mutations provide new insights of how the remaining starch granules are synthesized. The ss3 pii1 line still accumulates starch, while the phenotype of ss4 pii1 is stronger than that of ss4. Our results indicate first that SS4 initiates starch granule synthesis in the absence of PII1 albeit being limited to one large lenticular granule per plastid. Second, that if in the absence of SS4, SS3 is able to initiate starch granules with low efficiency, this ability is further reduced with the additional absence of PII1.
植物叶片中淀粉颗粒起始的控制是一个复杂的过程，需要有活性的酶，如淀粉合酶 4 和 3（SS4 或 SS3）和几种非催化蛋白，如淀粉起始蛋白 1（PII1）。在拟南芥叶片中，SS4 是控制淀粉颗粒起始的主要酶，但在其不存在的情况下，SS3 部分地履行了这一功能。这些蛋白质如何共同作用来控制淀粉颗粒的起始仍然难以捉摸。PII1 和 SS4 物理相互作用，并且 PII1 是 SS4 完全活性所必需的。然而，缺乏 SS4 或 PII1 的拟南芥突变体仍积累淀粉颗粒。将 pii1 KO 突变与 ss3 或 ss4 KO 突变相结合，提供了关于剩余淀粉颗粒如何合成的新见解。ss3 pii1 系仍然积累淀粉，而 ss4 pii1 的表型比 ss4 更强。我们的结果首先表明，尽管 SS4 在缺乏 PII1 的情况下将淀粉颗粒起始限制在每个质体的一个大透镜状颗粒中，但它仍能起始淀粉颗粒的合成。其次，如果缺乏 SS4，SS3 能够以低效率起始淀粉颗粒，而在进一步缺乏 PII1 的情况下，这种能力进一步降低。
