Figure 6.

Auxin Modulates PIP5K Expression and Transcript Accumulation.

(A) and (B) Four-day-old seedlings expressing the transcriptional reporters pPIP5K1:nlsGUS-GFP (A) and pPIP5K2:nlsGUS-GFP (B) were treated in liquid Arabidopsis medium containing 10 μM IAA for the times indicated in the bottom left corners and imaged immediately using confocal microscopy. Both transcriptional reporters were induced within 1 h of auxin treatment and maintained their induction over the period of 4 h studied. The pPIP5K2:nlsGUS-GFP marker was induced in the epidermal cell file (arrowheads in [B]) and all over the differentiation zone after 2 h of auxin treatment (asterisks in [B]). The fluorescence intensity is indicated as a gradient of color from low (black/dark blue) to high (yellow) fluorescence.

(C) and (D) Time-course experiment using 10 μM IAA for the times indicated in (C) and for 4 h in (D). RNA extracted from a 1-mm distal section of the root tips of 4-d-old seedlings was used. Means ± se are presented for three independent experiments. PIP5K1 transcript accumulated after 0.5 h of IAA treatment, and these levels were maintained over the time course of the experiment; this pattern of transcript accumulation is similar to that observed for the early auxin-inducible genes BDL and IAA3 (C). The PIP5K1 transcript accumulation after auxin treatment was abolished in arf7 arf19 double mutants (D).