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

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 Arabidopsis thaliana MscS-Like (MSL)10 have been well studied, but how MSL10 signals remains largely unknown. To uncover signaling partners of MSL10, we employed both a proteomic screen and a forward genetic screen; both unexpectedly implicated ER-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 MSL10 allele (msl10-3G, MSL10S640L), identified mutations in the synaptotagmin (SYT)5 and SYT7 genes. We also found that EPCSs were expanded in leaves of msl10-3G plants compared to the wild type. Taken together, these results indicate that MSL10 can be found at EPCSs and functions there, providing a new cell-level framework for understanding MSL10 signaling. In addition, placing a mechanosensory protein at EPCS provides new insight into the function and regulation of this type of subcellular compartment.