A peptide that regulates metalation and function of the Arabidopsis ethylene receptor

Ethylene signalling represents one of the classic hormonal pathways in plants, with diverse roles in development and stress responses. The dimeric ethylene receptor localizes to the endoplasmic reticulum (ER) and contains Cu(I) ions essential for ethylene binding and signalling. As for other vesicular cupro-proteins, the final step of Cu(I) maturation at the ER is undefined. We previously discovered that mutants in the Arabidopsis gene POLARIS (PLS), encoding a 36 amino acid peptide, exhibit enhanced ethylene signalling responses. Here we report a 1:2 thiol-dependent Cu(I):PLS2 complex, with an affinity of 3.79 (±1.5) x1019 M-2. We demonstrate PLS interactions with the transmembrane domain of receptor protein ETR1, the Cu(I) chaperones ATX1 and CCH, and Cu(I)-transporting P1B-type ATPase RAN1 at the ER. Formation of Cu(I)-dependent PLS-cuproprotein interactions at the ER provides a mechanism to modulate the metalation of ETR1, thereby regulating its activity and representing a novel mechanism for plant hormone receptor regulation. Overall design: To investigate the pls molecular phenotype, we carried out an RNA-seq analysis on loss-of-function pls mutant and PLS transgenic overexpressor seedlings, each compared with the wildtype seedlings of the same ecotype as controls. There were triplicates in each of the four groups (C24 pls mutant, C24 wild type, COL-0 PLS overexpressor, COL-0 wild type)