Isolation and Characterization of Sea Aster Salt-Stress Responsive Cysteine Protease Gene Obtained by a Hetero-probed Macroarray

To isolate and analyze salt-stress inducible genes in a halophyte, sea aster (Aster tripolium L.), we screened 5760 Arabidopsis cDNA clones by macroarray procedure using 33P-labeled cDNA targets synthesized from mRNAs isolated from NaCl treated and untreated sea aster seedlings. Seventeen Arabidopsis cDNAs were hetero-hybridized to NaCl inducible sea aster genes. These cDNAs were used as probes to isolate cDNA homologs from a sea aster cDNA library. One of the obtained cDNAs shared 71% amino acids identity with Arabidopsis cysteine protease (AtCysP) and named SaCysP (sea aster CysP). Northern blot analysis revealed that mRNAs corresponding to both SaCysP and AtCysP were induced by salt and osmotic stress in leaves. On the other hand, SASR21 mRNA encoding another CysP in sea aster was irresponsive to these stress in leaves but respond in roots. SaCysP and SASR21 genes may have a tissue-specific function in stress response by modulating their expression levels.