FODOR-DUNAI, C., FRICKE, I., POTOCKÝ, Martin, DORJGOTOV, D., DOMOKI, M., JURCA, M. E., OETVOES, K., ŽÁRSKÝ, Viktor, BERKEN, A., FEHER, A. The phosphomimetic mutation of an evolutionarily conserved serine residue affects the signaling properties of Rho of plants (ROPs). Plant Journal. 2011, 66(4), 669-679. ISSN 0960-7412. E-ISSN 1365-313X

Plant ROP proteins form a unique subgroup of Rho-type small G-proteins. Here we demonstrate that the phosphomimetic mutation of a serine conserved in all Rho proteins affects ROP signaling. We found that the S74E mutation prevented the binding of Medicago ROP6 to its upstream activator, PRONE-domain-containing RopGEF protein and abolished the PRONE-mediated nucleotide exchange in vitro. Structural modeling supported the hypothesis that phosphorylation of the S74 residue interferes with the binding of the PRONE-domain to the adjacent R76 residue which is critical in ROP-PRONE interaction. Moreover, we show that the capability of S74E mutant to activate the RRK1 kinase was reduced. This correlates with the morphology of tobacco pollen tubes expressing mutant forms of YFP:ROP6. The S74E mutation had no influence on pollen tube morphology. The presented data suggest that the phosphorylation of the serine corresponding to S74 in ROP6 is a general principle for regulating ROP signaling.