PIF4 and TCP4 function together to regulate high temperature-induced cell number suppression. A, Expression level of TCPs relative to an endogenous control, ACTIN2, at 21°C and 1 h of 28°C temperature treatment in young proliferating leaves of Col-0 plotted as 2^−(dCt). Values represent mean ± se (n = 6–8). B and C, GUS staining (scale = 1 cm, B) and its quantification (C) in leaves of TCP4:GUS reporter lines at 21°C or 28°C. Values represent mean ± se (n = 4). Stars indicate Student’s t test ^*P < 0.05. D, Rosette and leaf pictures of different genotypes grown at 21°C or 28°C at 20 DAS. The images were digitally extracted for size comparison. Scale = 1 cm. E, Quantification of rosette area in PIF4- and TCP4-related mutants grown at 21°C or 28°C (n = 45–55), P < 0.0001 (temperature), P < 0.001 (genotype). F, Quantification of leaf four area (n = 25), P < 0.001 (temperature), P < 0.05 (genotype). G, Average pavement cell number in the abaxial side of leaf four (n = 4–5 leaves), P < 0.0001 (temperature), P < 0.0001 (genotype). H, Average pavement cell area in the abaxial side of leaf four (n = 4–5 leaves), P < 0.001 (temperature), P < 0.001 (genotype). Box plot extends from 25th to 75th percentiles, where the center line represents the median and whiskers minimum and maximum values. The letters in (A) and (E–H) indicate significant differences based on two-way ANOVA and Tukey’s test (P < 0.05). Percent change between 21°C and 28°C is indicated above the graphs. The P-value for the interaction (genotype × temperature) is shown at the top of each plot. ns, not significant.