Regulation of nitrate transporter CHL1 phosphorylation by different nitrogen source

• Main Authors: Cheng-Syun Ho, 何承訓
• Other Authors: Yi-Fang Tsay
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/48305748130149882852

碩士 === 國立臺灣大學 === 植物科學研究所 === 92 === CHL1 is a dual-affinity nitrate transporter. Two functional modes of CHL1 are switched by phosphorylation and dephosphorylation at threonine residue 101: when phosphorylated, CHL1 function as a high-affinity nitrate transporter, whereas, when dephosphorylated, it functions as a low-affinity nitrate transporter. However, little is known about how CHL1 phosphorylation is regulated by the N-status of the plant, and what the physiological impacts of CHL1 phosphorylation are. To address these questions, nitrate uptake activity, CHL1 mRNA levels, CHL1 protein levels, as well as CHL1 phosphorylation levels were determined for plants exposed to high- or low- concentration of nitrate in the presence or absence of ammonium. When exposed to high concentration of nitrate, both CHL1 mRNA level, protein level as well as CHL1-mediated nitrate uptake activity showed transient increment followed by graduate decline. However, phosphorylation levels remain high 24 hour after exposing to high-concentration of nitrate. In contrast, when exposed to low-concentration of nitrate, CHL1 phosphorylation level showed transient increment then decline, but the protein levels remain high 24 hours after shift. These data indicated that phosphorylation level is high when the protein level is low. In addition, under certain condition, CHL1 protein level is not proportional to its mRNA level suggesting that CHL1is post-transcriptionally regulated in response to different nitrogen condition.