Abstract
Proline is a common osmolytes. We reported that an ACTCAT sequence acts as a cis-acting element involved in hypoosmolarity- and proline-responsive expression of proline dehydrogenase (ProDH) gene. Search of the database for cis-acting elements revealed that the ACTCAT sequence is similar to the GCN4 motif recognized by bZIPs. We examined whether bZIPs function as transcription factors for the ACTCAT sequence. Transient assay revealed that the ATB2 subgroup activate the expression of a reporter gene driven by the ACTCAT sequence. The transactivation activity of ATB2 subgroup was enhanced by hypoosmolarity. The sGFP::ATB2 fusion protein is localized in the nucleus. These suggest that the ATB2 subgroup functions as a transcriptional activator for hypoosmolarity-inducible expression of ProDH. To understand the role of ATB2 subgroup in plant, we analyzed transgenic Arabidopsis plants overexpressing the ATB2 subgroup cDNAs. In these plants, expression of ProDH was upregulated. Moreover, these plants showed decreased level of proline content.
