Molecular Characterization of a Salt‐Inducible Monodehydroascorbate Reductase from the Halophyte Avicennia marina

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 (high‐intensity 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 5′ upstream region of Am‐MDAR was iso...