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：

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蔗糖相关的 SnRK1a1 介导的 Opaque2 磷酸化调节玉米胚乳充盈

在玉米胚乳充盈过程中，蔗糖不仅作为储存-储备合成的碳骨架来源，而且还充当促进这一过程的刺激物。然而，人们对蔗糖和胚乳充盈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中心基因（）的表达，与储存储备积累相协调。我们发现蛋白激酶 SnRK1a1 可以减弱 O2 介导的反式激活，但蔗糖可以解除这种抑制。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，SnRK1a1 的突变会导致种子变大，籽粒重量和储存储备增加，而过度表达则会产生相反的效果。天然 (O2-OE)、磷酸死 (O2-SA) 和磷酸模拟 (O2-SD) 变体的过表达均增加了 100 粒重量。尽管 O2-SA 种子的籽粒尺寸较小，但它们具有较高的淀粉和蛋白质积累，导致玻璃体胚乳较大并增加了容重。 O2-SD 种子的籽粒尺寸较大，但储存储备和容重水平未发生变化。 O2-OE 种子显示出更高的籽粒尺寸和养分储存，就像 O2-SA 和 O2-SD 种子的混合物。总的来说，我们的研究发现了玉米胚乳充盈的一种新的调节机制。将 S41 鉴定为 O2 中 SnRK1 介导的磷酸化位点，为增强玉米储存储备积累和产量提供了潜在的工程靶点。