Molecular cloning and characterization of genes encoding BURP domain-containing protein in the mangrove, Brugniera gymnorrhiza

We cloned and characterized four independent genes encoding BURP domain-containing proteins from mangrove, Bruguiera gymnorrhiza, two as cDNA (BgBDC2 and BgBDC3) and the other two as genomic DNA (S2 and L3). The putative coding sequences of S2 and L3 were computationally analysed and designated as BgBDC1 and BgBDC4, respectively. These four genes are highly homologous to the dehydration-responsive RD22 gene from Arabidopsis thaliana. Amino acid sequences deduced from the four isolated genes contain characteristic repeated regions, which consist of repeated units whose consensus sequence is similar to that of RD22. The repeated regions, however, differ from each other and from RD22 by the copy number of the repeated unit; x copies in BgBDCX (x=1, 2, 3, and 4), while five copies in RD22. Northern blot analysis probed with BgBDC3 cDNA showed that the amount of RNA hybridized to the probe was retained in the top leaves following 500 mM NaCl treatment, while it distinctly decreased in the lower leaves. Desiccation treatment and exogenous abscisic acid (ABA) treatment also decreased the amount in all leaves. The results indicate that the regulatory mechanisms in B. gymnorrhiza for the expression of RD22 homologues are different from that of RD22.