RNAseq of drought treated Populus trichocarpa

To identify genes that are drought-responsive we conducted drought (soil water depletion) experiments on 3-month-old *P*. *trichocarpa *clonal plants. The plants undergo five different stages based on the appearance of their shoots and leaves during the drought experiments. Stage I: The shoot and leaves are green, and the leaves are well-spread. Stage II: The leaves are droopy. Stage III: The shoot is droopy, and the leaves are partially dry. Stage IV: The leaves are brown and totally dry. Stage V: The shoot is brown. With fully irrigation, the soil water content is 74% and the xylem water content is 80.6%. Plants in Stage III (Day 5) are under a mild drought state. The soil and xylem water content in Stage III dropped to 33% and 75.3%, respectively. Stage IV (Day 6-10) is a severe drought state where the soil and xylem water content continued decreasing to 29% and 74.3%, respectively in Day 7. The stressed plants from Stage I-IV could all recover in 3 days after rehydration, but the plants in Stage V could not recover after rehydration. Overall design: We collected the xylem tissue from plants (1) without drought treatment (Control, Day 0), (2) under mild drought stress (Stage III, Day 5), (3) under severe drought stress (Stage IV, Day 7) followed by RNA-seq analysis.