Arabidopsis cytoplasmic N-acetyltransferase, as the ortholog of RimL in E. coli, controls flowering time via the autonomous pathway

Although some plant nuclear acetyltransferases mediate development, the function(s) of cytoplasmic ones remain unknown. We characterized a putative Arabidopsis N-acetyltransferase 1 gene (AtATF1) orthologous to the Escherichia coli RimL-type N-acetyltransferase gene. Protoplast transient assays and expression pattern analyses in the gene root tips revealed that AtATF1 was localized in the cytoplasm. To investigate the physiology of an ATF-defective mutant, we used RNAi to simultaneously silence three paralogous genes, AtATF1, AtATF2, and AtATF3. Interestingly, the mutant exhibited severely late flowering under long days and short days, although late flowering was slightly reversed by gibberellin or vernalization treatment. We observed increased transcript levels of FLOWERING LOCUS C (a central floral repressor) and its paralogs, MADS AFFECTING FLOWERING 4 and 5 in the mutant. In contrast, transcript levels of FLOWERING LOCUS T and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 were decreased. Notably, the mutant also had downregulated transcription of FLOWERING LOCUS D, but not three LDL homologs, an autonomous pathway floral factor. We conclude that cytoplasmic AtATF may regulate the flowering time via the autonomous pathway.