THE FUSICOCCIN RECEPTOR OF PLANTS IS A MEMBER OF THE 14-3-3-SUPERFAMILY OF EUKARYOTIC REGULATORY PROTEINS

The receptor for the wilt-inducing phytotoxin fusicoccin was purified to homogeneity from plasma membranes of Commelina communis as a complex with the radioligand [H-3]9'-nor-8'-hydroxyfusicoccin. The preparation consisted of two polypeptides with apparent molecular masses of 30.5 kDa and 31.5 kDa and with isoelectric points of around pH 5.2 and 5.3, respectively. The proteins were N-terminally blocked. Internal amino acid sequences were obtained for both polypeptides of the fusicoccin-binding complex. Sequence information, as well as subsequent immunological analysis, proved that both polypeptides are members of the eukaryotic 14-3-3 family, which comprises structurally conserved regulatory proteins of widespread occurrence and a wide range of functions. 14-3-3 isoform(s) constituting the fusicoccin receptor are distinguishable from other cellular 14-3-3 proteins by their tight association with the plasma membrane. Applying temperature-induced Triton X-114 phase separation experiments, they, as well as the target enzyme of fusicoccin action, the H+-ATPase, partitioned into the phospholipid-rich fraction which contains the most hydrophobic proteins. The results discussed herein provide a basis for the elucidation of the molecular mechanism of fusicoccin action.