Proteome-wide cellular thermal shift assay reveals novel crosstalk between brassinosteroid and auxin signaling

We demonstrated that bikinin changed the thermal stability of some of its target proteins as well as several known or putative interacting proteins of Arabidopsis GSK3s. By combining the thermal- and the phospho-proteomes of bikinin we uncovered the auxin carrier PIN-FORMED1 (PIN1) as a novel substrate of the Arabidopsis GSK3s. We showed that inhibition the kinase activity of GSK3s by brassinosteroids or the specific chemical inhibitor bikinin led to the loss of PIN1 polarity, revealing a novel crosstalk between brassinosteroid and auxin signaling. Hence, our study demonstrates the applicability of CETSA MS in plant intact cells for identification of small-molecule targets and for discovery of novel protein-protein interactions.