PyMPV17, the MPV17 Homolog of Pyropia yezoensis (Rhodophyta), Enhances Osmotic Stress Tolerance in Chlamydomonas

Pyropia yezoensis is the most cultivated marine red algae in East Asia and is desiccation tolerant. PyMPV17, a desiccation stress response gene isolated from P. yezoensis, shares significant sequence similarity with mouse MPV17. A yeast knock-out mutant for SYM1, an MPV17 ortholog, could not grow on ethanol-containing medium at 38°C. Expression of PyMPV17 in yeast sym1 cells complemented the ethanol growth defect at 38°C, which suggests that PyMPV17 is a functional ortholog of SYM1. PyMPV17-green fluorescent protein (GFP) fluorescence was detected in mitochondria and PyMPV17 transcription was upregulated under desiccation stress in P. yezoensis gametophytes. Transcription of the PyMPV17 gene also increased in response to H2O2 and abscisic acid treatments. When PyMPV17 was introduced into the green alga Chlamydomonas, transgenic cells grew better than control cells on agar plates containing mannitol. Total malondialdehyde content in the transgenic cells was lower than that in the control cells under stress conditions. These results suggest that PyMPV17 reduces oxidative damage and contributes to the mechanism underlying tolerance to osmotic stress in red algae.