Sucrose synthases are not involved in starch synthesis in Arabidopsis leaves

第一作者：Maximilian M. F. F. Fünfgeld

第一单位：德国马克斯·普朗克分子植物生理学研究所

通讯作者：Totte Niittylä

 Abstarct 

假设1：Many plants accumulate transitory starch reserves in their leaves during the day to buffer their carbohydrate supply against fluctuating light conditions, and to provide carbon and energy for survival at night. It is universally accepted that transitory starch is synthesized from ADP-glucose (ADPG) in the chloroplasts. 

很多植物会在白天于叶片中暂时积累淀粉储备，以便缓冲由于光照条件波动所导致的碳水化合物供应波动，并为夜间的生存提供碳源和能量。人们普遍认为，暂时性的淀粉是由叶绿体中的ADP-葡糖（ADPG）合成的。

假设2：However, the consensus that ADPG is made in the chloroplasts by ADPG pyrophosphorylase has been challenged by a controversial proposal that ADPG is made primarily in the cytosol, probably by sucrose synthase (SUS), and then imported into the chloroplasts. 

然而，之前普遍认为的ADPG是在叶绿体中由ADPG焦磷酸化酶产所合成这一假设一直受到另一假设的挑战，即认为ADPG主要是由蔗糖合酶SUS在胞质中合成，然后被转运进叶绿体。

主要研究：To resolve this long-standing controversy, we critically re-examined the experimental evidence that appears to conflict with the consensus pathway. 

为了解决这个长期存在的争议，作者重新严苛审视了似乎与先前假设相冲突的实验证据。

结果-高阶突变体支持假设1：We show that when precautions are taken to avoid artefactual changes during leaf sampling, Arabidopsis thaliana mutants that lack SUS activity in mesophyll cells (quadruple sus1234) or have no SUS activity (sextuple sus123456) have wild-type levels of ADPG and starch, while ADPG is 20 times lower in the pgm and adg1 mutants that are blocked in the consensus chloroplastic pathway of starch synthesis. 

作者发现，当在叶片采样过程中通过采取预防措施避免人为因素干扰，拟南芥SUS四突植株sus1234（叶肉细胞中缺乏SUS活性）或者六突植株sus123456（全株均没有SUS活性）具有与野生型相当的ADPG和淀粉水平；而在pgm和adg1突变体中，ADPG的水平要比野生型低20倍，后两种突变的基因是第一个假设中在叶绿体中淀粉合成的关键基因。

结论：We conclude that the ADPG needed for starch synthesis in leaves is synthesized primarily by ADPG pyrophosphorylase in the chloroplasts.

因此，作者得到结论，叶片中淀粉合成所需的ADPG主要是由叶绿体中的ADPG焦磷酸化酶所合成。

 Totte Niittylä 

doi: https://doi.org/10.1038/s41477-022-01140-y

Journal: Nature Plants

Published date: April 28, 2022