Arabidopsis GLP4 is localized to the Golgi and binds auxin in vitro

Hormones are critical for cell differentiation, elongation, and division. The plant hormone auxin plays vital roles in plant growth and development and is essential for various physiologic processes. Previous studies showed that germin-like proteins (GLPs) are involved in multiple physiologic and developmental processes and that several GLP members could bind different auxin molecules. Here we showed that Arabidopsis thaliana GLP4 gene, which has a length of 660 bp and encodes a 219-aa polypeptide, contains the conserved auxin-binding region box A and binds indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid (2,4-D) with low affinity, but not a-naphthaleneacetic acid, in vitro, by using assays equilibrium dialysis and nuclear magnetic resonance. This binding character is different from that of auxin-binding protein 1, which does not bind 2,4-D. GLP4 is highly transcribed in various tissues, but it shows low transcription in roots and during embryo development. In addition, transcription of GLP4 is stimulated by auxin treatment. Subcellular localization studies indicated that GLP4 protein is localized in the Golgi compartment and the N-terminus of GLP4 is crucial for its proper localization, which suggests that GLP4 may be involved in Golgi-dependent developmental processes.