Gyeongsang National University Jinju, Kyongsang-namdo, Republic of Korea
Body of Abstract: Transcription factors are involved in plant stress responses, and the bZIP family, to which HY5 and bZIP17 belong, are known to play key role in various stress responses. HY5 is known to have multiple physiological and transcriptional functions in plant development, including photomorphogenesis. bZIP17, along with bZIP28, is an endoplasmic reticulum (ER)-anchored transcription factor that is involved in the unfolded protein response (UPR) under ER stress conditions. In this regard, bZIP28 regulates the expression of ER stress response genes in competition with HY5 and its function as a transcription factor is relatively well studied, but the relationship with HY5 and the transcriptional role of bZIP17 are largely unknown. Therefore, in this study, we characterize the role of bZIP17 as a transcription factor removing its transmembrane domain. Further, identified its subcellular localization to the nucleus, and analyzed its protein-protein binding interaction with HY5 and its function under stress. Using yeast two-hybrid and BiFC assay, examined their binding and found that HY5 and bZIP17 interaction in vivo. To investigate the function of HY5 and bZIP17 in ER stress, we compared the phenotypes of hy5 mutant and 35S::bZIP17-SRDX transformant with an EAR repression domain (SRDX) in tunicamycin (Tm) and azetidine-2-carboxylic acid (AZC) medium, and found that the hy5 mutant was tolerant and the 35S::bZIP17-SRDX transformant was sensitive, suggesting that they have opposite functions in ER stress. To gain further insights into their function at the transcriptional level, we found that when treated with dithiothreitol (DTT) or mannitol, the expression of bZIP17 in hy5 mutant plants increased and the expression of HY5 remained unchanged or decreased in 35S::bZIP17-SRDX transgenic plants, indicating that HY5 and bZIP17 are involved in each other's expression under ER stress conditions. Overall, the results suggest that bZIP17 may play an important role in stress response through interaction with HY5.