dda1-1 mutants display shorter hypocotyls in the dark. (A) Hypocotyl length of 7-day-old Col, dda1-1, and DDA1-GR seedlings grown under a 16 h light/8 h dark photoperiod (white columns) or in the dark (black columns). A minimum of 12 seedlings was assayed for each background and growth condition. Error bars represent the standard error. t-test for dark treatment, P <0.0001 (Col×dda1-1); P <0.001 (Col×dda1-1/+); P <0.0001 (Col+DEX×DDA1-GR+DEX). (B) The same experiment as in (A) but using dda1-1, ted5-1, and dda1-1 ted5-1 seedlings. t-test for light treatment, P <0.0001 (dda1-1×ted5-1); P <0.0001 (dda1-1×dda1-1 ted5-1). ted5-1 and dda1-1 ted5-1 were not significantly different (P <0.2). t-test for dark treatment, P <0.0001 (dda1-1×ted5-1); P <0.0001 (dda1-1×dda1-1 ted5-1); P <0.05 (ted5-1×dda1-1 ted5-1). (C) RT-PCR analysis of DDA1 transcript levels in 7-day-old Col, ted5-1, and dda1-1 ted5-1 seedlings following 0 h or 2 h exposure to dark conditions. RT-PCR products were detected by blotting and probing with gene-specific probes, following either 15 cycles (DDA1) or 10 cycles (ACT2) of amplification.