Review: Source–sink regulation in crops under water deficit ($) (Trends Plant Sci)

Plants have a remarkable ability to coordinate cellular activities across huge distances, yet we have only a basic understanding of how these remote activities are coordinated. A review by Rodrigues et al. summarizes what we know about the relationship between source (e.g., photosynthetic tissues) and sinks (e.g., growing tissues or seeds), and particularly how this relationship is affected by water deficit (WD). As the authors describe, greater insights into whole-plant physiological integration is needed in order to develop high-yielding, drought-tolerant crops. The authors summarize how both source and sink activities are affected by WD, at physiological as well as cellular and biochemical levels. As examples, WD closes stomata and reduces gas exchange, leading to a decrease in photosynthetic carbon fixation. WD also decrease xylem flow, causing also a decrease in phloem flow and the movement of sugars into the sink tissues. The authors discuss results from genetic studies that reveal the contributions of specific transcription factors and hormones, as well as the metabolic integrators SnRK1 and TOR.  Finally, they describe the many questions that need additional research. This excellent, accessible review would be useful for students to help them integrate molecular and physiological stress responses. (Summary by Mary Williams) Trends Plant Sci  10.1016/j.tplants.2019.04.005