Cloning and characterization of the stress-induced bZIP gene ZmbZIP60 from maize

ZmbZIP60 is a member of the bZIP transcription factor family in maize. Expression of ZmbZIP60 is strongly induced by a wide spectrum of stresses, including dehydration, high salinity, abscisic acid and tunicamycin treatments. A truncated form of ZmbZIP60, without a transmembrane domain (ZmbZIP60ΔC) and fused with GFP, is localized in the nucleus, suggesting the translocation of the native protein to the nucleus by release from the membrane. Yeast one-hybrid analysis showed that both ZmbZIP60 and ZmbZIP60ΔC had transcriptional activity. The expression of ZmbZIP60 in Arabidopsis bzip60 mutant partially restored the induction of BiP3 transcription under TM treatment, which indicated that ZmbZIP60 may play a role in the signal transduction of endoplasmic reticulum stress. Overexpression of ZmbZIP60 in wild-type Arabidopsis displayed enhanced bolting trends when subjected to dithiothreitol stress. Real-time PCR analysis revealed that some key genes in floral transition, including CO, FT, and AP1, were up- or down-regulated in ZmbZIP60-overexpressing plants, which may reveal the functional difference of ZmbZIP60 from AtbZIP60.