Nuclear translocation of OsMADS25 facilitated by OsNAR2.1 in reponse to nitrate signals promotes rice root growth by targeting OsMADS27 and OsARF7

Nitrate is an important nitrogen source and signal molecule to regulate plant growth and development. Although several components of the nitrate signaling pathway have been identified, the detailed mechanisms are still not clear. Our previous results showed that OsMADS25 could regulate root development in response to nitrate signal, but the mechanism is still unknown. Here, we try to answer two key questions, how does OsMADS25 move from the cytoplasm to the nucleus and what are the direct target genes that OsMADS25 could activate to regulate root growth once it moved to nucleus in response to nitrate signal. Our results firstly found that OsMADS25 could move from the cytoplasm to the nucleus in the presence of nitrate and this movement is in an OsNAR2.1 dependent manner. Secondly, our ChIP-seq, ChIP-qPCR, Y1H and LUC experiments showed that OsMADS25 could directly activate the expression of OsMADS27 and OsARF7, which were reported to associate with root growth. Thirdly, we found that OsMADS25-RNAi lines, Osnar2.1 mutant and OsMADS25-RNAi Osnar2.1 lines exhibited significantly reduced root growth than that of wild type in response to nitrate supply, and expression of OsMADS27 and OsARF7 was significantly suppressed in these lines. Collectively, this study reveals a new mechanism that OsMADS25 interacts with OsNAR2.1, which is required for nuclear accumulation of OsMADS25, further to promote the expression of OsMADS27 and OsARF7 and root growth in a nitrate dependent manner.