Molecular cloning and transcriptional regulation of two γ-carbonic anhydrase genes in the green macroalga Ulva prolifera

Ulva prolifera O.F. Muller (Ulvophyceae, Chlorophyta) is well known as a typical green-tide forming macroalga which has caused the world's largest macroalgal blooms in the Yellow Sea of China. In this study, two full-length gamma-carbonic anhydrase (gamma-CA) genes (Up gamma CA1 and Up gamma CA2) were cloned from U. prolifera. Up gamma CA1 has three conserved histidine residues, which act as an active site for binding a zinc metal ion. In Up gamma CA2, two of the three histidine residues were replaced by serine and arginine, respectively. The two gamma-CA genes are clustered together with other gamma-CAs in Chlorophyta with strong support value (100% bootstrap) in maximum likelihood (ML) phylogenetic tree. Quantitative real-time PCR (qRT-PCR) analysis showed that stressful environmental conditions markedly inhibited transcription levels of these two gamma-CA genes. Low pH value (pH 7.5) significantly increased transcription level of Up gamma CA2 not Up gamma CA1 at 12 h, whereas high pH value (pH 8.5) significantly inhibited the transcription of these two gamma-CA genes at 6 h. These findings enhanced our understanding on transcriptional regulation of gamma-CA genes in response to environmental factors in U. prolifera.