Wang Zizhang, Li Hao, Weng Yuxiang
Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
iScience. 2024 Jun 8;27(7):110217. doi: 10.1016/j.isci.2024.110217. eCollection 2024 Jul 19.
Sucrose is the transport form of carbohydrate in plants serving as signal molecule besides nutrition, but the signaling is elusive. Here, neutral invertase 8 (OsNIN8) mutated at G461R into OsNIN8m, which increased its charge and hydrophobicity, decreased hydrolysis of sucrose to 13% and firmer binding to sucrose than the wildtype. This caused downstream metabolites and energy accumulation forming overnutrition. Paradoxically, division of subinitials in longitudinal cell lineages was only about 15 times but more than 100 times in wildtype, resulting in short radicle. Further, mutation of OsNIN8 into deficiency of hydrolysis but maintenance of sucrose binding allowed cell division until ran out of energy showing the association but not hydrolysis gave the signal. Chemically, sucrose binding to OsNIN8 was exothermic but to OsNIN8m was endothermic. Therefore, OsNIN8m lost the signal function owing to change of thermodynamic state. So, OsNIN8 sensed sucrose for cell division besides hydrolyzed sucrose.
蔗糖是植物中碳水化合物的运输形式，除了作为营养物质外，还充当信号分子，但这种信号传导尚不清楚。在这里，中性转化酶8（OsNIN8）在G461R处突变为OsNIN8m，这增加了其电荷和疏水性，将蔗糖水解降低至13%，并且与蔗糖的结合比野生型更紧密。这导致下游代谢物和能量积累，形成营养过剩。矛盾的是，纵向细胞谱系中初始细胞的分裂在突变体中仅约为野生型的15倍，但在野生型中超过100倍，导致胚根短小。此外，将OsNIN8突变为水解缺陷但保持蔗糖结合能力，使细胞分裂能够持续到能量耗尽，这表明是蔗糖结合而非水解发出了信号。从化学角度来看，蔗糖与OsNIN8的结合是放热的，但与OsNIN8m的结合是吸热的。因此，由于热力学状态的改变，OsNIN8m失去了信号功能。所以，OsNIN8除了水解蔗糖外，还能感知蔗糖以进行细胞分裂。
