A serine/threonine protein kinase gene isolated by an in vivo binding procedure using the Arabidopsis floral homeotic gene product, AGAMOUS

During the course of characterizing fragments bound to an Arabidopsis floral homeotic protein AGAMOUS in vivo, a gene encoding a putative serine/threonine protein kinase was found on one of the fragments. The deduced 426 amino acid residues of the gene, named APK2a, are 65% identical to a previously reported Arabidopsis serine/threonine protein kinase, APK1a. The gene is composed of 6 exons and maps at 10 cM from the upper end of chromosome 1. Northern hybridization experiments indicated that the gene is strongly expressed in leaves, moderately in roots, and very weakly in flowers. Further in situ analysis of the expression in floral buds showed that the APK2a gene is expressed at pedicels, is not expressed at the floral organ primordia of wild type floral buds, but is moderately expressed in the floral organ primordia of the agamous mutant. In vitro binding assay suggests that the AGAMOUS protein binds to a sequence similar to, but different from, the known MADS-binding consensus sequences, the CArG box, located 3' downstream of the APK2a gene. These results suggest that APK2a gene expression is negatively regulated by the AG protein, A close homologue of the APK2a gene, named APK2b, was also isolated from the Arabidopsis cDNA library. The expression pattern of the APK2b gene differs from that of APK2a. It is strongly expressed in leaves, moderately in flowers, and weakly in roots.