Background

Nitrogen not only influences plant growth and development but also participates in numerous signaling pathways. Plant evolved an efficient and sophisticated nitrate signaling regulatory network (NSRN) in roots for adapting to terrestrial environments. However, our understanding of when and how a complete NSRN was established remains limited.

Results

Here, we systematically identified the Homologous genes encoding 20 key components involved in the NPF6.3(NRT1.1/CHL1)-centered NSRN and elucidated their evolutionary histories. Further analysis of six core components (NPF6, CIPK, CPK, NLP, TCP, NRT2) revealed that most clades containing functional genes appeared at the ancestral node of seed plants. Moreover, the putatively functional clade members exhibit root-preferential expression patterns in gymnosperms. Protein interaction predictions indicate that, except for TCP, the interactions among other components were already established in gymnosperms and conserved in angiosperms. These results suggest that a relatively complete NSRN was likely formed at the ancestral node of seed plants. Meanwhile, the appearance of putatively functional clade members of non-core components at different evolutionary nodes likely contributes to the increasing complexity of NSRN.

Conclusions

Our study provides better understanding of the evolutionary trajectory of the NPF6.3(NRT1.1/CHL1)-centered NSRN in land plants and the adaptive mechanisms of nitrogen utilization since plant terrestrialization.