Abstract
Lotus japonicus NIN is one of key regulators for nodulation. nin mutants display aberrant root hair curing and defects in infection thread (IT) formation and in cortical cell division (CCD). We have demonstrated that NIN has abilities to induce IT formation and CCD. However, NIN protein function and its molecular mechanisms, by which NIN regulates nodulation processes, have not yet been elucidated, although the secondary structure prediction of NIN protein has suggested that it may act as a transcription factor. When we expressed NIN fused with GAL4-DNA binding domain in tobacco cells, expression of a reporter gene, of which promoter possesses GAL4-binding DNA sequences, was induced, indicating that NIN is a transcriptional activator. We searched genes whose expression is upregulated by NIN using publicly available L. japonicus transcriptome data base and found 19 genes as candidates for NIN targets. ChIP assay and EMSA showed that two genes, at least, were directly targeted by NIN. DEX-inducible form of NIN protein induced expression of these genes depending on DEX. Furthermore, we are analyzing function of these factors in nodulation processes.
