The transcription factor OsMADS61 positively regulates root elongation and nitrogen use efficiency in rice

Plant roots have evolved adaptive strategies mediated by transcriptional networks to cope with fluctuating nitrogen (N) forms and availability. However, the mechanisms linking root-foraging responses to N use efficiency (NUE) in crops remain poorly understood. Here, we show that rice exhibits enhanced root elongation under nitrate compared with ammonium, particularly under low N supply, suggesting a specific regulatory role for nitrate in root morphogenesis. We identify the transcription factor OsMADS61 as a key regulator of nitrate-dependent root morphological and physiological responses, as well as NUE, especially under N-limited conditions. OsMADS61 acts as a transcriptional activator of nitrate metabolism by directly binding to OsNRT2.1 and OsNR2 promoters. Nitric oxide produced via the nitrate reductase pathway, under the control of nitrate-responsive OsMADS61, precisely triggers cell proliferation in the root meristem. Moreover, single-nucleotide polymorphisms in the OsMADS61 promoter may be associated with differential root-foraging responses to nitrate availability. Therefore, enhancing N-adaptive root responses to optimize N uptake and assimilation represents a promising strategy for breeding crops with high NUE.