Salinity poses a major threat to crop productivity. Our earlier work has used the halophytic plant Avicennia
marina as a model organism for mining genes that function in salinity stress tolerance. Here we report the
isolation and characterization of a monodehydroascorbate reductase (MDAR) from this plant. MDAR plays
a key role in regeneration of ascorbate from monodehydroascorbate for reactive oxygen species scavenging. A
cDNA clone encoding MDAR was isolated from a cDNA library created from a salt-stressed leaf of A. marina.
A transit peptide at the N-terminal region of Am-MDAR suggested chloroplastic localization. Transcript
profiling for Am-MDAR revealed that the gene is expressed in response to salinity and oxidative stress (highintensity
light, H2O2, and iron overload). The genomic clone of Am-MDAR contained 16 exons. The presence
of two identical MDAR transcripts, with and without exon 3, indicated possible exon skipping. A 1167-bp
fragment corresponding to the 59 upstream region of Am-MDAR was isolated, and transient reporter gene
expression studies revealed it to be a functional promoter. In-silico analysis of this sequence revealed the
presence of putative light- and abiotic-stress regulatory elements. The possible reasons for changes in gene
expression during stress in relation to the host plant’s stress tolerance mechanisms are discussed.