Early auxin-induced genes encode short-lived nuclear proteins.

The plant growth hormone indoleacetic acid (IAA) transcriptionally activates gene expression in plants. Some of the genes whose expression is induced by IAA encode a family of proteins in pea (PS-IAA4 and PS-IAA6) and Arabidopsis (IAA1 and IAA2) that contain putative nuclear localization signals that direct a beta-glucuronidase reporter protein into the nucleus. Pulse-chase and immunoprecipitation experiments have defined 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 beta alpha alpha motif similar to the beta-sheet DNA-binding domain found in prokaryotic repressors of the Arc family. Based on these data, we suggest that plant tissues express short-lived nuclear proteins as a primary response to IAA. We propose that these proteins act as activators or repressors of genes responsible for mediating the various auxin responses.