Figure Legends
FIGURE 1 (a) Photosynthetic capacity (i.e., maximal light- and CO2-saturated rate of oxygen evolution) per leaf area, (b) leaf dry mass per area, (c) level of chlorophyll a + bper leaf area, and (d) chlorophyll a/b ratio in leaves of IT (red columns) and SW (blue columns) plants that were grown in low light/warm temperature growth conditions (LLW), low light/cool temperature growth conditions (LLC), high light/warm temperature growth conditions (HLW), or high light/cool temperature growth conditions (HLC). Mean values ± standard deviations (n = 3 or 4); groups that share the same letters are not considered statistically different, and groups that do not share the same letters are considered statistically different based on one-way ANOVA and post hoc Tukey–Kramer HSD tests.
FIGURE 2 Light response of reduction state of the primary electron acceptor of photosystem II (QA, quantified by chlorophyll fluorescence using the equation 1 − qL) of leaves from IT (red circles) and SW (blue squares) plants grown under (a) LLW and (b) HLC. Mean values ± standard deviations (n = 3); statistically significant differences between ecotypes based on Student’s t -tests are indicated with asterisks (* =P  < 0.05, ** = P  < 0.01, *** =P  < 0.001); n.s . = not significantly different.
FIGURE 3 Relative transcript abundance (via RT-qPCR) of (a)CBF1 , (b) CBF2 , and (c) CBF3 in leaves of IT (red columns) and SW (blue columns) plants that were grown in LLW, LLC, HLW, or HLC conditions. Values are presented relative to the expression level for each respective gene in the IT ecotype grown under LLW. Mean values ± standard deviations (n = 3); groups that share the same letters are not considered statistically different, and groups that do not share the same letters are considered statistically different based on one-way ANOVA and post hoc Tukey–Kramer HSD tests.
FIGURE 4 (a) Hierarchical clustering of the log2 expression data (via RNAseq) for 7,933 genes with an adjusted P- value below 0.01 in one of the pairwise comparisons for differential expression between ecotypes and growth conditions. The three biological replicates for each growth condition/ecotype set are shown as separate columns. (b) Log2 expression data (via RNAseq) for IT and SW in HLC relative to LLW for genes previously characterized as regulated by CBF1–3 in Col-0 (Jia et al. 2016; Park et al. 2018). CIPK25 and KIN2 are protein kinases and EGR2 is a protein phosphatase, all participating in cold acclimation signaling (Thomashow 1999; Ding et al. 2019). COR47, LTI30, and LTI29 each are cold and drought-induced dehydrin proteins (Puhakainenet al. 2004). SUS1 and GOLS3 are stress-induced sucrose synthase and galactinol synthase enzymes, respectively (Maruyama et al.2009). COR15B is essential for chloroplast membrane integrity during freezing (Thalhammer, Hundertmark, Popova, Seckler & Hincha 2010).
FIGURE 5 (a) Photosynthetic capacity (light- and CO2-saturated rate of oxygen evolution) per leaf area, (b) leaf dry mass per area, (c) level of chlorophyll a + bper leaf area, and (d) chlorophyll a/b ratio in leaves of IT (red columns), it:cbf123 (light red columns), SW (blue columns), and sw:cbf123 (light blue columns) plants that were grown in LLW or HLC. Mean values ± standard deviations (n = 6); Groups that share the same letters are not considered statistically different, and groups that do not share the same letters are considered statistically different based on one-way ANOVA and post-hoc Tukey–Kramer HSD tests.
FIGURE 6 (a) Leaf thickness of IT (red column), it:cbf123 (light red column), SW (blue column), and sw:cbf123 (light blue column) plants that were grown in HLC, as well as representative images of leaf cross-sections for (b) IT, (c) it:cbf123 , (d) SW, and (e) sw:cbf123 . For (a), mean values ± standard deviations (n = 3); groups that share the same letters are not considered statistically different, and groups that do not share the same letters are considered statistically different based on one-way ANOVA and post-hoc Tukey–Kramer HSD tests.
FIGURE 7 (a) Rosette diameter of IT (red column), it:cbf123 (light red column), SW (blue column), and sw:cbf123 (light blue column) after 40 days of growth in HLC, as well as images of representative (b) IT, (c) it:cbf123 , (d) SW, and (e) sw:cbf123 plants. For (a), mean values ± standard deviations (n = 5); groups that share the same letters are not considered statistically different, and groups that do not share the same letters are considered statistically different based on one-way ANOVA and post-hoc Tukey–Kramer HSD tests.
FIGURE 8 (a–c) Cellular electrolyte leakage from mature leaves, and (d) images of mature leaves with photosystem II photochemical efficiency (visualized via false colors based on Fv/Fm values) from IT (red circles), it:cbf123 (light red circles), SW (blue squares), and sw:cbf123 (light blue squares) plants grown under LLW or HLC. For (a,b) mean values (n = 3). For (c), mean values ± standard deviations (n = 3); groups that share the same letters are not considered statistically different, and groups that do not share the same letters are considered statistically different based on one-way ANOVA and post-hoc Tukey–Kramer HSD tests.
FIGURE 9 Percent survival after an overnight freezing treatment (16 h at −10°C) of IT (red columns), it:cbf123 (light red columns), SW (blue columns), and sw:cbf123 (light blue columns) plants grown under LLW or HLC. Mean values ± standard deviations (n = 3 plates, each of which contained 40 plants); groups that share the same letters are not considered statistically different, and groups that do not share the same letters are considered statistically different based on one-way ANOVA and post-hoc Tukey–Kramer HSD tests.
FIGURE 10 Relative transcript abundance (via RT-qPCR) for (a) AT5G44565, (b) SUS1, (c) LCR69, (d) AT1G13930, and (e) RCI2A in leaves of IT (red columns), it:cbf123 (light red columns), SW (blue columns), and sw:cbf123 (light blue columns) plants grown in LLW or HLC. All values are normalized based on the expression levels of IT in LLW. Mean values ± standard deviations (n = 3); groups that share the same letters are not considered statistically different, and groups that do not share the same letters are considered statistically different based on one-way ANOVA and post-hoc Tukey–Kramer HSD tests. SUS1 is a stress induced sucrose synthase (Barratt et al. 2009).
FIGURE 11 Relative transcript abundance (via RT-qPCR) for (a)GolS3 , (b) CIPK25, (c) KIN2 , (d) EGR2 , (e)COR78, (f) COR15A , (g) LTI30 , (h) COR15B , and (i) AT1G21790 in leaves of IT (red columns), it:cbf123 (light red columns), SW (blue columns), and sw:cbf123 (light blue columns) plants grown under LLW or HLC. CIPK25 and KIN2 are protein kinases and EGR2 is a protein phosphatase, all participating in cold acclimation signaling (Thomashow 1999; Ding et al. 2019). LTI30 is a drought-induced dehydrin protein (Puhakainen et al. 2004). GOLS3 is a galactinol synthase enzyme (Fowler & Thomashow 2002). COR15B is essential for chloroplast membrane integrity during freezing (Thalhammer et al. 2010). All values are normalized based on the expression levels of IT under LLW. Mean values ± standard deviations (n = 3); groups that share the same letters are not considered statistically different, and groups that do not share the same letters are considered statistically different based on one-way ANOVA and post-hoc Tukey–Kramer HSD tests.