cDNA cloning of a lectin-like gene preferentially expressed in freshwater from the macroalgaUlva limnetica(Ulvales, Chlorophyta)

SUMMARY The macroalgal species Ulva limnetica Ichihara et Shimada was investigated to understand the molecular mechanism of its tolerance or adaptation to freshwater. We detected a 19 kDa protein by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which accumulated in greater amounts in freshwater conditions compared with marine conditions. The band was excised and the partial amino acid sequence was determined by Edoman degradation. Based on the sequences, we isolated the corresponding cDNA by the rapid amplification of cDNA ends (RACE) technique. The constructed, full-length cDNA was 1272 bp in length, consisting of 198 bp 5′-non-coding region, an open reading frame of 840 bp (279 amino acids), 233 bp 3′-non-coding region and poly (A) tail. The protein encoded by the cDNA showed 30% identity and 45% similarity to lectin isolated from Ulva pertusa Kjellman, and we named this gene ULL (encoding Ulva limnetica lectin-like protein). Northern blot analysis demonstrated that the expression level of the ULL in the freshwater-cultured sample was higher than in the seawater-cultured sample.