During maize endosperm filling, sucrose not only serves as a source of carbon skeletons for storage-reserve synthesis but also acts as a stimulus to promote this process. However, the molecular mechanisms underlying sucrose and endosperm filling are poorly understood. In this study, we found that sucrose promotes the expression of endosperm-filling hub gene (), coordinating with storage-reserve accumulation. We showed that the protein kinase SnRK1a1 can attenuate O2-mediated transactivation, but sucrose can release this suppression. Biochemical assays revealed that SnRK1a1 phosphorylates O2 at serine 41 (S41), negatively affecting its protein stability and transactivation ability We observed that mutation of results in larger seeds with increased kernel weight and storage reserves, while overexpression of causes the opposite effect. Overexpression of the native (O2-OE), phospho-dead (O2-SA), and phospho-mimetic (O2-SD) variants all increased 100-kernel weight. Although O2-SA seeds exhibit smaller kernel size, they have higher accumulation of starch and proteins, resulting in larger vitreous endosperm and increased test weight. O2-SD seeds display larger kernel size but unchanged levels of storage reserves and test weight. O2-OE seeds show elevated kernel dimensions and nutrient storage, like a mixture of O2-SA and O2-SD seeds. Collectively, our study discovers a novel regulatory mechanism of maize endosperm filling. Identification of S41 as a SnRK1-mediated phosphorylation site in O2 offers a potential engineering target for enhancing storage-reserve accumulation and yield in maize.

中文翻译：

---

蔗糖相关 SnRK1a1 介导的 Opaque2 磷酸化调节玉米胚乳填充


在玉米胚乳灌浆过程中，蔗糖不仅作为储藏储备合成的碳骨架来源，而且还作为促进这一过程的刺激。然而，人们对蔗糖和胚乳填充的分子机制知之甚少。在这项研究中，我们发现蔗糖促进胚乳填充枢纽基因 （） 的表达，与储藏储备积累相协调。我们发现蛋白激酶 SnRK1a1 可以减弱 O 2 介导的反式激活，但蔗糖可以释放这种抑制。生化测定显示 SnRK1a1 在丝氨酸 41 （S41） 处磷酸化 O2，对其蛋白质稳定性和反式激活能力产生负面影响我们观察到，突变导致更大的种子，增加籽粒重量和储存储备，而过表达会导致相反的效果。天然 （O2-OE）、磷酸死亡 （O2-SA） 和磷酸模拟物 （O2-SD） 变体的过表达均增加了 100 粒核的重量。尽管 O2-SA 种子表现出较小的籽粒大小，但它们具有更高的淀粉和蛋白质积累，导致更大的玻璃体胚乳和增加的测试重量。O2-SD 种子显示较大的籽粒大小，但储存储备和测试重量水平不变。O2-OE 种子显示出较高的籽粒尺寸和养分储存，就像 O2-SA 和 O2-SD 种子的混合物一样。总的来说，我们的研究发现了玉米胚乳填充的一种新的调控机制。在 O2 中鉴定 S41 为 SnRK1 介导的磷酸化位点为提高玉米的储存储备积累和产量提供了一个潜在的工程靶点。