New Paper from Jake Brunkard and Pat Zambryski

Significance

Plant cells are connected to each other by plasmodesmata (PD), membrane-bound cytosolic channels that cross the cell wall. Diverse molecules, ranging from metabolites to small RNAs and proteins, can traffic between plant cells via PD. During development, PD transport is regulated to control the redistribution of carbohydrates from mature leaves that photosynthesize excess sugars to young leaves that rapidly consume sugars. Here, we show that the ancient eukaryotic TARGET OF RAPAMYCIN (TOR) metabolic signaling network controls PD transport in plants. TOR is a protein kinase that is activated by nutrients, including sugars, and then coordinates growth with nutrient availability. Our study demonstrates that TOR has evolved new roles in plants by regulating cell–cell connectivity via PD.

Abstract

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.

https://www.pnas.org/content/early/2020/02/11/1919196117.abstract?etoc