Figure 6.

Alternative transcriptional start sites for PDX1.2 as a function of heat stress in eudicots. A, Scheme depicting the TSSs identified in PDX1.2 from Arabidopsis. In the absence of heat stress, the TSS1 is 156 nucleotides upstream of +1 and within the HSE (colored red). In the presence of heat stress, the TSS2 is 83 nucleotides upstream of the translational start (+1). The TATA box region is depicted by the gray box. The corresponding sequence of the region until the start codon (ATG) is given below the scheme. The boxed Gs in the sequence represent the precise starts of TSS. The open reading frame is depicted by the arrow-headed box in black in the scheme. B, Quantitative analysis of PDX1.2 expression in Arabidopsis wild type (Col-0) in the absence (22°C) and presence (37°C) of heat stress using the primer pairs depicted by arrowheads in A and which correspond to transcript levels of the 5′-UTR (from TSS1, left panel) and the ORF (right panel). C, Quantification of luciferase activity by transient expression in tobacco as a function of temperature using the constructs depicted in the scheme, which correspond to the fusion of the promoter of PDX1.2 to LUC. The wild-type HSE is depicted by the pale red line in the scheme and by the hashed line when mutated. REN was used as the transformation reporter. The LUC/REN ratio for wild type and mutated HSE is given in the absence (22°C) and presence (37°C) of heat stress.