The CKH1/EER4 Gene Encoding a TAF12-Like Protein Negatively Regulates Cytokinin Sensitivity in Arabidopsis thaliana

The recessive ckh1 (cytokinin hypersensitive 1) mutant of Arabidopsis thaliana shows hypersensitivity to cytokinins, which promote proliferation and greening of calli. The CKH1 gene encodes a protein resembling TAF12 (TATA BOX BINDING PROTEIN ASSOCIATED FACTOR 12), which is a component of transcription factor IID (TFIID)- and histone acetyltransferase-containing complexes in yeast and animals. Microarray analyses revealed that a substantially greater number of genes responded to a low level of cytokinins in the ckh1 mutant than in the wild type. However, expression of cytokinin primary response genes was not significantly affected by the ckh1 mutation. These results suggest that the CKH1 protein regulates a set of genes involved in late signaling processes governing a range of cytokinin responses, including cell proliferation and differentiation.