| Summary: | 博士 === 國防醫學院 === 生命科學研究所 === 97 === Ions, essential nutrients for higher plants, also act as signal molecules. Little is known about how plants sense changes in soil nutrient concentrations. In this study, analysis of an uptake- and sensing-decoupled mutant showed that the dual-affinity nitrate transporter CHL1 functions as a nitrate sensor. Previous studies showed that T101-phosphorylated CHL1 is a high-affinity nitrate transporter, while T101-dephosphorylated CHL1 is a low-affinity transporter. Here, primary nitrate responses in CHL1T101D and CHLT101A transgenic plants showed that the phosphorylated and dephosphorylated CHL1 lead to a low- and high-level response, respectively. In vitro and in vivo studies showed that, in response to low nitrate concentrations, protein kinase CIPK23 can phosphorylate T101 of CHL1 to maintain a low-level primary response. CHL1, the first ion sensor identified in higher plants, uses dual-affinity binding and phosphorylation switching to sense a wide range of nitrate concentrations in the soil and thus trigger different levels of nitrate response.
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