EARLY AUXIN-INDUCED GENES ENCODE SHORT-LIVED NUCLEAR PROTEINS

The plant growth hormone indoleacetic acid (IAA) transcriptionally act ivates gene expression in plants. Some of the genes whose expression i s induced by IAA encode a family of proteins in pea (PS-IAA4 and PS-IA A6) and Arabidopsis (IAA1 and IAA2) that contain putative nuclear loca lization signals that direct a beta-glucuronidase reporter protein int o the nucleus. Pulse-chase and immunoprecipitation experiments have de fined the t1/2 of the PS-IAA4 and PS-IAA6 proteins to be 8 and 6 min, respectively. Their most prominent feature is the presence of a betaal phaalpha motif similar to the beta-sheet DNA-binding domain found in p rokaryotic repressors of the Arc family. Based on these data, we sugge st that plant tissues express short-lived nuclear proteins as a primar y response to IAA. We propose that these proteins act as activators or repressors of genes responsible for mediating the various auxin respo nses.