Carbohydrate dynamics in Populus trees under drought: an expression atlas of genes Carbohydrate dynamics in Populus trees under drought: an expression atlas of differentially expressed genes across leaf, stem, and root

Nonstructural carbohydrates (NSC) management in response to drought stress is vital to understanding drought acclimation in trees. However, the molecular mechanisms underlying such processes remain unclear for most forest trees. Poplars are considered a model species for studying woody plants' molecular mechanisms. They are known to deploy a passive, symplastic sugar loading strategy, relying on sugars' concentration gradient through the plasmodesmata rather than on active sugar transport. Under drought conditions, tight regulation is needed to sustain long periods of stress and maintain water content. This study subjected young poplar trees (P. alba) to drought stress, following a combined analysis of sugar content and gene expression profile (RNAseq). We analyzed the expression of 29 gene families related to NSC signaling, translocation, and metabolism along three tree compartments (leaves, shoots, and roots). Starch depletion was evident in all organs, while soluble sugars accumulated only in the leaves, with an overall whole-tree decrease of ~30% in total sugar content. Our findings highlight relevant genes that specialize in triggering drought metabolism, starch depletion, sugar immobility, and osmotic adjustment. Broadly up-regulated genes are highlighted, as well as tissue-specific ones. This research provides a broad overview of the molecular process underlining NSC dynamics under drought in poplar trees.