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. 2018 Dec 17;9:1873. doi: 10.3389/fpls.2018.01873

FIGURE 1.

FIGURE 1

Bud set-associated genes in poplar are sensitive to low ambient temperature. (A) Bud set scores for hybrid poplar (Populus tremula x P. alba) plants grown under SD and three different temperatures (21, 18, and 15°C) for 9 weeks. (B) Comparative analysis of hybrid poplar bud stage progression in plants grown under SD and three different temperatures (21, 18, and 15°C) over 4 weeks. Asterisks denote significant differences between hybrid poplar plant groups (n = 8) grown at different temperatures (Kruskal–Wallis test followed by pairwise Wilcox test; ∗P < 0.05, ∗∗P < 0.01). (C) Venn diagram representing the intersection between genes with SNPs associated with bud set and that show robust diurnal oscillations (cut-off = 0.8) under light/dark cycles (LD) and constant temperature (25°C, HH) or photothermocycles (25°C during the day, 12°C during the night, HC). 172 genes (lilac) show robust diurnal rhythms only under LDHH, 134 genes (pink) show diurnal rhythms only under LDHC and 135 genes (fuchsia) oscillate under both conditions, respectively. (D,E) Clusters of genes that show diurnal expression within 0–11 h under LDHC (D, mean = pink) and within 12–23 h under LDHC (E, mean = pink). The line chart demonstrates how photothermocycles (LDHC) promote diurnal oscillation of poplar PDLDELTA (D) and CBF4 genes (E). (F,G) Clusters of genes that show diurnal expression within 0–11 h under LDHH (F, mean = lilac) and within 12–23 h under LDHH (G, mean = lilac). The line chart demonstrates how photothermocycles (LDHC) disrupt the diurnal oscillation of poplar CCR1 (F) and PUR7 genes (G).