Figure 5.

Functional characterization of MYB74oe lines. (A) qPCR analysis of the transcriptional activation of MYB74 by heat and osmotic stress conditions. Gene expression is given relative to the MYB74 expression in untreated control plants, which has been set to 1. (B) Seed germination kinetics in wild-type Arabidopsis (Col-0) and the two conditionally MYB74 overexpressing lines. Seed coat rupture (SCR) and endosperm rupture (ER) time course. Different letters indicate significant differences (p < 0.05) in germination of the tested genotypes at t₅₀(h), indicated by the dashed lines. Two-way ANOVA analysis with a subsequent Tukey–Kramer post hoc test was employed to statistically assess the data. (C) Phenotypic analysis of primary root growth under control (Ctrl) and osmotic stress condition (Stress). To apply osmotic stress, young seedlings were grown on plates containing 300 mM mannitol. Scale bar = 1 cm. (D) Violine plot showing the relative primary root elongation response of 4 days-old seedlings that were transferred to plates containing 300 mM mannitol and grown for another 7 days. The primary root elongation of each genotype grown under control conditions was set to 100%. The boxes and whiskers display the median, quartiles, and extremes of the compared datasets (n = 20). The colored regions indicate the density distribution of the samples in each genotype and condition. Different letters refer to significant differences between the means of the compared datasets analyzed by ANOVA and a Tukey–Kramer post hoc test (p ≤ 0.05). (E) Stacked bar plots representing the relative quantification of endogenous IAA, IAM, and ABA contents in wild-type Arabidopsis and the two MYB74oe lines. The content of each metabolite in wild-type seedlings (Col-0) was set to 1. The metabolite levels in the MYB74oe lines were expressed in reference to the wild-type levels. The stacks show mean values ±SE (n = 3). The same letters for each metabolite in the different genotypes refer to a lack of significant differences between the means of the compared datasets analyzed by ANOVA and a Tukey–Kramer post hoc test (p ≤ 0.05). (F) Survival rate of Col-0 and MYB74oe seedlings 7 days after a heat shock treatment (42°C, 30 min). The conditional overexpression of MYB74 reduced the survival rate of the seedlings considerably. (G) Comparison of the stomatal aperture of wild-type (Col-0) and MYB74oe lines under control conditions. The overexpression of MYB74 significantly increases stomatal aperture. Student’s t-test: ^***p ≤ 0.001.