Faculty of Bio-Industry, Tokyo University of Agriculture, 196 Yasaka, Abashiri, 099-2493, Japan.
Faculty of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate, 041-0821, Japan.
Mar Environ Res. 2020 Jul;159:105004. doi: 10.1016/j.marenvres.2020.105004. Epub 2020 May 16.
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.
海水中氮源的减少会导致可食用的红色海藻条斑紫菜变色，并诱导编码氨、硝酸盐和尿素转运蛋白的基因表达。在本研究中，我们证明低温也会导致这种具有重要经济价值的海藻变色。因此，我们研究了低温诱导变色的调控机制。当条斑紫菜藻体在 0、5 和 10°C 下孵育时，藻体生长缓慢并变色，同时藻红蛋白含量降低。在 0°C 下用氮源施肥不能恢复这种变色，这表明氮吸收的缺陷导致低温诱导的变色。许多氮转运基因的表达水平在低温下降低。我们提出，低温介导的铵、硝酸盐和尿素转运蛋白基因表达的抑制促进了条斑紫菜对氮源的吸收减少，从而导致变色。这个过程与在正常培养温度下氮缺乏条件下条斑紫菜变色的已知机制不同。
