Chemical screening of inhibitors specific for MdDOX-Co that cause an apple columnar tree-shape.

MdDOX-Co, the ectopic expression of which is considered to cause the columnar tree shape, belongs to the 2-oxoglutarate-dependent dioxygenase (2ODD) family. It adds a hydroxyl group to position 12 of gibberellins. However, the 2ODD enzymes related to gibberellin biosynthesis and catabolism are phylogenetically distinct from MdDOX-Co. Thus, it is possible that substrates other than gibberellins exist in MdDOX-Co. To identify the previously unidentified substrate(s) of MdDOX-Co, we searched for MdDOX-Co-specific inhibitors. Chemical screening using GC-MS was performed to investigate the effects of 2,400 compounds that inhibited the catalytic reaction of MdDOX-Co, but not the catabolic reaction of GA 2-oxidase, an enzyme involved in gibberellin catabolism. By applying these two compounds in Arabidopsis, a chemical designated as TPDD that did not inhibit gibberellin biosynthesis was selected. The structure-activity relationships among the TPDD analogs were also obtained.