Zhao Shuping, Zhang Chuyan, Jiao Jiao, Zhang Yao, Jiang Tao, Wu Peng, Feng Kai, Li Liangjun
School of Horticulture and Gardens, Yangzhou University, Yangzhou, 225009, China.
Joint International Research Laboratory of Agriculture and Agri-Product Safety of Ministry of Education of China, Yangzhou University, Yangzhou, 225009, China.
Plant Cell Rep. 2025 Jan 3;44(1):21. doi: 10.1007/s00299-024-03408-3.
NnNAC100-NnSBEII modules enhance starch content of the rhizome in Nelumbo nucifera Gaertn. Nelumbo nucifera Gaertn. is a popular aquatic vegetable and traditional Chinese medicine whose quality and taste are mainly determined by the starch. Although starch-related genes have been functionally characterized, the regulated mechanism of enzyme (SBE) remains unclear. In this study, we identified and functionally elucidated the functions of NnSBEII and NnNAC100 using transient overexpression of NnSBEII and NnNAC100 in rhizomes of lotus, and it significantly increased the amylopectin content and total starch content. Accordingly, functional complementation assay in defective Arabidopsis also showed that NnSBEII compensated for the low content of starch in the mutant sbe2.2. In addition, overexpression of NnSBEII and NnNAC100 significantly increased the content of starch in transgenic lines. Consistently, opposite results were observed under the background of repressed NnSBEII and NnNAC100 in rhizomes of lotus. Furthermore, yeast one-hybrid and dual-luciferase assays revealed that NnNAC100 could directly bind to the NnSBEII promoter and promote the expression of NnSBEII. Transient overexpression of NnNAC100 upregulated NnSBEII expression significantly, while the expression level of AtSBE2.2 in transgenic Arabidopsis overexpressing NnNAC100 was higher than that of WT, which indicated that NnNAC100 promoted the synthesis of amylopectin by enhancing the expression of NnSBEII. In addition, we found that NnSBEII could form a complex protein by interacting with soluble starch synthase (NnSS2) to increase the activity of the SBEII enzyme. These results reveal a novel mechanism that the NnNAC100-NnSBEII-NnSBEII/NnSS2 module regulates amylopectin biosynthesis and these will provide insights into the broader implications of the regulation mechanism of starch biosynthesis.
NnNAC100-NnSBEII模块提高了莲（Nelumbo nucifera Gaertn.）根茎中的淀粉含量。莲是一种广受欢迎的水生蔬菜和传统中药，其品质和口感主要由淀粉决定。尽管与淀粉相关的基因已被进行功能表征，但酶（SBE）的调控机制仍不清楚。在本研究中，我们通过在莲根茎中瞬时过表达NnSBEII和NnNAC100来鉴定并功能解析它们的功能，结果显示其显著增加了支链淀粉含量和总淀粉含量。相应地，在缺陷型拟南芥中的功能互补试验也表明NnSBEII弥补了突变体sbe2.2中淀粉含量的降低。此外，NnSBEII和NnNAC100的过表达显著增加了转基因株系中的淀粉含量。同样，在莲根茎中抑制NnSBEII和NnNAC100的背景下观察到了相反的结果。此外，酵母单杂交和双荧光素酶试验表明NnNAC100可直接结合到NnSBEII启动子上并促进NnSBEII的表达。NnNAC100的瞬时过表达显著上调了NnSBEII的表达，而过表达NnNAC100的转基因拟南芥中AtSBE2.2的表达水平高于野生型，这表明NnNAC100通过增强NnSBEII的表达促进了支链淀粉的合成。此外，我们发现NnSBEII可通过与可溶性淀粉合酶（NnSS2）相互作用形成复合蛋白来提高SBEII酶的活性。这些结果揭示了一种新机制，即NnNAC100-NnSBEII-NnSBEII/NnSS2模块调控支链淀粉的生物合成，这将为淀粉生物合成调控机制的更广泛意义提供见解。
