Figure 3.

The ARE Contributes to Downregulation of the Pi Transporter in Response to As(V).

(A) Diagram showing the relative sizes of the three classes of downregulated genes in response to 30 μM As(V) and 30 μM Pi identified in a microarray analysis. As(V) > Pi, genes preferentially downregulated by As(V); As(V) < Pi, genes preferentially downregulated by Pi; As(V) = Pi, genes downregulated equally in response to both. For microarray analysis, wild-type plants were grown on Johnson medium with 1 mM Pi for 7 d, transferred to -Pi for 2 d, and finally to -Pi medium supplemented with 30 μM As(V) or 30 μM Pi (8 h).

(B) Analysis of ARE frequency in 0.5 kb of the promoter regions of genes in the As(V)>Pi and As(V)<Pi classes. The table shows observed and expected ARE numbers assuming random distribution. Significant overrepresentation is highlighted (χ² test, P < 0.05).

(C) Diagram showing wild-type (PHT1;1p-I/II) and mutated versions (PHT1;1p-I/IIm, PHT1;1p-Im/II, and PHT1;1p-Im/IIm) of the PHT1;1 promoter region fused to luciferase (PHT1;1-LUC). The ARE in the PHT1;1 promoter (I and II; black) was mutated sequentially (Im and IIm; diagonal stripes) by PCR site-directed mutagenesis.

(D) Kinetic analysis of LUC activity in transgenic plants expressing the PHT1;1p-I/II, PHT1;1p-I/IIm, PHT1;1p-Im/II, or PHT1;1p-Im/IIm constructs, in response to 30 μM As(V) (1.5 h). Values represent data from analysis of 12 independent lines of each construct; mean ± sd.