Abstract
Abstract Malate dehydrogenase (MDH) is an enzyme that catalyzes the interconversion of malate and oxaloacetate substrates and is widely distributed from prokaryotes to eukaryotes. It plays crucial roles in many important metabolic pathways and includes different isoforms based on coenzyme specificity and cellular localization. To study MDH in rhodophytes, we obtained a full-length cDNA clone (here designated PhMDH) encoding an NAD-malate dehydrogenase in the marine red alga Pyropia haitanensis. The nucleotide sequence of PhMDH was 1521 bp, including an open reading frame (ORF) of 984 bp. The amino acid sequence showed 73% identity with other MDHs in proteobacteria. Two MDH-like domains were detected in the 5–145 and 156–320 regions. Real-time fluorescent quantitative PCR (qPCR) was used to examine mRNA expression levels during the gametophyte and sporophyte phases. The transcription of PhMDH in the gametophyte was barely detectable, whereas PhMDH in the sporophyte showed a much higher expression level. The activity of PhMDH in the filamentous sporophyte was approximately double that of the leafy gametophyte. Considering these results, we suggest that PhMDH may be localized in the cytosol and play a role in carbon fixation in the sporophyte stage.
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