Unbiased proteomic and forward genetic screens reveal that mechanosensitive ion channel MSL10 functions at ER-plasma membrane contact sites in <i>Arabidopsis thaliana</i>.

Mechanosensitive (MS) ion channels are an evolutionarily conserved way for cells to sense mechanical forces and transduce them into ionic signals. The channel properties of <i>Arabidopsis thaliana</i> MscS-Like (MSL)10 have been well studied, but how MSL10 signals remains largely unknown. To uncover signaling partners of MSL10, we employed a proteomic screen and a forward genetic screen; both unexpectedly implicated endoplasmic reticulum-plasma membrane contact sites (EPCSs) in MSL10 function. The proteomic screen revealed that MSL10 associates with multiple proteins associated with EPCSs. Of these, only VAMP-associated proteins (VAP)27-1 and VAP27-3 interacted directly with MSL10. The forward genetic screen, for suppressors of a gain-of-function <i>MSL10</i> allele (<i>msl10-3G, MSL10^S640L</i>), identified mutations in the <i>synaptotagmin (SYT)5</i> and <i>SYT7</i> genes. We also found that EPCSs were expanded in leaves of <i>msl10-3G</i> plants compared to the wild type. Taken together, these results indicate that MSL10 associates and functions with EPCS proteins, providing a new cell-level framework for understanding MSL10 signaling. In addition, placing a mechanosensory protein at EPCSs provides new insight into the function and regulation of this type of subcellular compartment.