A diurnally regulated dehydrin from Avicennia marina that shows nucleo-cytoplasmic localization and is phosphorylated by Casein kinase II in vitro

Dehydrins have a key role in protecting plants from dehydration stress. We report here the isolation of two cDNAs coding for the same dehydrin, AmDHN1 and AmDHN1a from salt stressed leaves of Avicennia marina (Forsk.) Vierh. by EST library screening. AmDHN1 was found to contain a retained intron that was absent in AmDHN1a. AmDHN1 expression in the context of various environmental stresses was investigated. In leaves, AmDHN1 shows a diurnal pattern of regulation and is induced only by mannitol application. In roots, AmDHN1 is rapidly induced by salinity (NaCl) and dehydration stress (PEG and mannitol). A fragment of 795 bp corresponding to the 5′ upstream region of AmDHN1 was isolated by TAIL-PCR. In silico analysis of this sequence reveals the presence of putative stress regulatory elements (ABRE, DRE, MYB and MYC binding sequences). Putative phosphorylation sites for Casein kinase II were identified in the AmDHN1a ORF. In vitro phosphorylation of Escherichia coli expressed Trx-AmDHN1a by Casein kinase II was observed that was reversed by Shrimp Alkaline Phosphatase treatment. A putative nuclear targeting domain was identified in the translated AmDHN1a ORF and stably transformed AmDHNIa-GFP was found to show nucleo-cytoplasmic localization in tobacco guard cells. As observed for maize Rab17, the phosphorylation of AmDHN1a may contribute to its nuclear localization.