The legume-rhizobia symbioses lead to the formation of a novel adaptive complex organ, termed the root nodule, which arises from cortical cell division and rhizobial infection in the root. Lipochitin oligosaccarides, Nod-Factors (NFs) secreted by rhizobia, are responsible for the onset of nodule development. Here we describe the characterization of Lotus japonicas, Nod factor Signaling Pathway2 (LjNSP2) protein that belongs to the plant GRAS family of transcription factors. Yeast two-hybrid analysis indicates that LjNSP2 alone has a transcription-stimulating ability and for this the SH2(src-homology2)-like domain, vital for function of STAT proteins is required. The ADG4 (the activation domain of GAL4)-LjNSP2 fusion coupled with BDG4 (the DNA binding domain of GAL4)-LjNSP2 increased the expression level, whereas the ADG4-Ljnsp2-1 mutant fusion did not, indicating that LjNSP2 interacts with itself to form a homodimer and this depends on the SH2-like domain. Based on the evidence, we discuss the action of LjNSP2, compared with that of the family of animal-specific STAT transcription factors, which induce developmental programmes in response to external stimuli.
Keywords: Lotus japonicus; NSP2; Nod factor; activator; transcription factor.