mRNA abundance of OsUGT90A1 in different rice tissues and in transgenic Arabidopsis plants at warm (control) and cold temperatures. (a) Relative expression of OsUGT90A1 in leaves and roots at control temperatures (28/25 °C day/night, 12-h photoperiod) and after continuous exposure to 4 °C for 7 h, as determined by qPCR analysis. (b) Quantification of real-time firefly luciferase (LUC) intensity in whole plants of homozygous Arabidopsis lines transformed with a 500-bp OsUGT90A1-promoter::LUC construct before (control) and after chilling treatment at 4 °C for 3 h. (c) Normalized LUC)bioluminescent activity at 28 °C in rice protoplast transiently transfected with plasmids containing a 500-bp OsUGT90A1-promoter::LUC reporter gene. (d) Time-series analysis of OsUGT90A1 expression in leaves and roots during exposure to 4 °C, as determined by qPCR analysis. Relative expression levels at 7, 24, and 48 h were normalized to the level of the warm-temperature control (time 0, set as 1). JAP, japonica accession Krasnodarskij 3352 (haplotype I; Fig. 1a); IND: indica accession Carolino 164 (haplotype IX; Fig. 1a). JAP::LUC, a 500-bp OsUGT90A1 promoter fragment from Krasnodarskij 3352 fused to LUC; IND::LUC, a 500-bp OsUGT90A1 promoter fragment from Carolino 164 fused to LUC. Data are means (±SD), n=3 (a, b, d), n=10 (c). Significant differences between means are indicated and were determined using two-tailed Student’s t-tests: *P<0.05; **P<0.01; ***P<0.001.