ABSTRACT
The unfolded protein response (UPR) or the endoplasmic reticulum (ER) stress response occurs when folding and maturation of secretory and membrane proteins are impaired in the ER. The UPR induces a number of genes that encode ER-localized molecular chaperones and folding enzymes to increase folding capacity in the ER. We have identified Tunicamycin Induced 1 (TIN1), an Arabidopsis gene that is highly induced during the UPR. We have shown that TIN1 protein is localized in the ER but its physiological function remains to be elucidated. In the present study we generated and analyzed transgenic Arabidopsis plants expressing TIN1 under CaMV35S promoter to obtain insights into the physiological role of TIN1. We found that although TIN1-overexpressing plants grew as did wild-type plants under ambient laboratory conditions, their pollen grains exhibited abnormal surface morphology. The result suggests a specific role of TIN1 in secretion of proteins and/or lipids during pollen development.
ABSTRACT
We have conducted transcriptome analysis and have identified a number of genes that are upregulated by treatment with the endoplasmic reticulum (ER) stress inducer tunicamycin. Here we focused on one particular gene of unknown function. This gene, designated tunicamycin induced 1 (TIN1), encodes an open reading frame consisting of 424 amino acids with a putative signal peptide. TIN1 orthologs are present in several plant species, including poplar, rice, and moss, but not in other organisms, including yeast and animals. Transcriptional induction of TIN1 by ER stress was regulated in part by AtbZIP60, a membrane-bound transcription factor activating many ER stress-responsive genes. In agreement with increases of TIN1 transcripts, the TIN1 protein accumulated in response to tunicamycin treatment. It was localized at the ER when fused with a fluorescent protein. These results represent a first step toward elucidating the molecular function of TIN1.
