A FRET sensor for live-cell imaging of MAP kinase activity in Arabidopsis

摘要： The catalytic activity of mitogen activated protein kinases (MAPKs) is dynamically modified in plants. Since MAPKs have been shown to play important roles in a wide range of signaling pathways, the ability to monitor MAPK activity in living plant cells would be valuable. Here we report the development of a genetically encoded MAPK activity sensor for use in Arabidopsis thaliana. The sensor is composed of yellow and blue fluorescent proteins, a phosphopeptide binding domain, a MAPK substrate domain, and a flexible linker. Using in vitro testing, we demonstrated that phosphorylation causes an increase in the F?rster resonance energy transfer (FRET) efficiency of the sensor. FRET efficiency can therefore serve as a readout of kinase activity. We also produced transgenic Arabidopsis lines expressing this sensor of MAPK activity (SOMA) and performed live-cell imaging experiments using detached cotyledons. Treatment with NaCl, the synthetic flagellin peptide flg22, and chitin all led to rapid gains in FRET efficiency. Control lines expressing a version of SOMA in which the phosphosite was mutated to an alanine did not show any substantial FRET changes. We also expressed the sensor in a conditional loss-of function double-mutant line for the Arabidopsis MAPK genes MPK3 and MPK6. These experiments demonstrated that MPK3/6 are necessary for the sensor’s NaCl-induced FRET gain, while other MAPKs are likely contributing to the chitin and flg22-induced FRET increases. Taken together, our results suggest that SOMA is able to dynamically report MAPK activity in living plant cells.