The reduced availability of nitrogen sources in seawater leads to discoloration of the edible red seaweed Pyropia yezoensis and induces the expression of genes encoding ammonium, nitrate and urea transporters. In the present study, we demonstrate that low temperatures can also cause discoloration of this economically important seaweed. Thus, we addressed regulatory mechanisms of cold-inducible discoloration. When P. yezoensis thalli were incubated at 0, 5 and 10°C, the thalli exhibited retarded growth and discoloration, along with reduced phycoerythrin contents. Fertilization with nitrogen sources did not recover this discoloration at 0°C, suggesting that defects in nitrogen absorption cause low temperature-induced discoloration. The expression levels of many nitrogen transporter genes were reduced at low temperature. We propose that low temperature-mediated repression of ammonium, nitrate and urea transporter gene expression promotes the reduced absorption of nitrogen sources in P. yezoensis, thereby leading to discoloration. This process is different from the well-known mechanism underlying discoloration in P. yezoensis under nitrogen-deficient conditions at normal culture temperature.
Bibliographical noteFunding Information:
We thank Dr. Keiji Sasuga of the Suzuyo Research Institute, Co. Ltd., Shizuoka, Japan, for his support with statistical analysis of the data. Puja Kumari is an International Research Fellow supported by JSPS with Postdoctoral Fellowship for Research in Japan (Standard). This work was supported in part by the KAKENHI grants from the MEXT ( 15H04539 and 18F18388 ).
- Gene expression
- Low temperature
- Nitrogen transporter
- Photosynthetic pigment
- Pyropia yezoensis
- Ammonium Compounds
- Rhodophyta/growth & development