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 50 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