Developmental phenotypes of the reil1-1 reil2-1 mutant under standard and suboptimal temperature regimes. reil1-1 reil2-1 and Arabidopsis Col-0 wild-type plants were compared under constant temperature and temperature-shift regimes. A, Constant standard temperature conditions at 20°C/18°C (day/night). Mutant and wild-type plants reached vegetative developmental stage ∼1.10 (Boyes et al., 2001) approximately 4 weeks after transfer to soil. Note that the mutant had a mild pointed-leaves phenotype (Van Lijsebettens et al., 1994; Horiguchi et al., 2012). B, Constant low-temperature conditions at 10°C/8°C (day/night). Mutant plants survived at least 13 weeks after germination and transfer to soil but remained extremely dwarfed, with final rosette diameters less than 1 cm and only five to seven visible leaves. C, Temperature shift from the 20°C to the 10°C regime. In contrast to the acclimating wild type, growth and development of the mutant were arrested. Mutant plants survived at least 13 weeks at low temperatures. D, Temperature shift from the 20°C to a 4°C/4°C (day/night) regime. Mutant plants and the wild type were growth arrested. Mutant survival was not tested. E, Inverse temperature shift from the 10°C to the 20°C regime. In contrast to the deacclimated wild type, mutant plants entered a rapid flowering program reminiscent of stress-induced early flowering (Xu et al., 2014). Temperature shifts in C and D were performed at developmental stage ∼1.10 of wild-type and mutant plants at the stages shown in A at week 0. Note that plant age is given by week prior to or post developmental stage ∼1.10. Plants were germinated under sterile conditions (Schmidt et al., 2013) and transferred to soil at stage 1.02-1.03 (i.e. at −6 weeks [10°C] or −4 weeks [20°C]). The inverse temperature shift from 10°C to 20°C (E) was performed when the wild type reached stage ∼1.10 at 10°C. Cocultivated mutant plants had stage 1.02-1.03. Arrowheads within the experimental schemes indicate the time at which representative photographs of n ≥ 10 plants per experiment were taken. Bars = 1 cm.