Department of Plant and Microbial Biology, University of California, Berkeley CA 94720;
Plant Gene Expression Center, US Department of Agriculture, Agricultural Research Service, Albany, CA 94710.
Proc Natl Acad Sci U S A. 2020 Mar 3;117(9):5049-5058. doi: 10.1073/pnas.1919196117. Epub 2020 Feb 12.
The coordinated redistribution of sugars from mature "source" leaves to developing "sink" leaves requires tight regulation of sugar transport between cells via plasmodesmata (PD). Although fundamental to plant physiology, the mechanisms that control PD transport and thereby support development of new leaves have remained elusive. From a forward genetic screen for altered PD transport, we discovered that the conserved eukaryotic glucose-TOR (TARGET OF RAPAMYCIN) metabolic signaling network restricts PD transport in leaves. Genetic approaches and chemical or physiological treatments to either promote or disrupt TOR activity demonstrate that glucose-activated TOR decreases PD transport in leaves. We further found that TOR is significantly more active in mature leaves photosynthesizing excess sugars than in young, growing leaves, and that this increase in TOR activity correlates with decreased rates of PD transport. We conclude that leaf cells regulate PD trafficking in response to changing carbohydrate availability monitored by the TOR pathway.
从成熟的“源”叶到发育中的“汇”叶，糖的协调再分配需要通过胞间连丝（PD）对糖在细胞间的运输进行严格调控。尽管这对植物生理学至关重要，但控制 PD 运输并支持新叶发育的机制仍然难以捉摸。通过对 PD 运输改变的正向遗传学筛选，我们发现保守的真核葡萄糖-TOR（雷帕霉素靶蛋白）代谢信号网络限制了叶片中的 PD 运输。促进或破坏 TOR 活性的遗传方法和化学或生理处理表明，葡萄糖激活的 TOR 会降低叶片中的 PD 运输。我们进一步发现，在光合作用产生多余糖分的成熟叶片中，TOR 的活性明显高于正在生长的年轻叶片，并且 TOR 活性的增加与 PD 运输速率的降低相关。我们的结论是，叶片细胞通过 TOR 途径监测碳水化合物可用性的变化来调节 PD 运输。
