NAC1 is a NAC family gene that mediates auxin signaling to promote lateral root development in Arabidopsis. The study shows that NAC1 is induced by auxin and acts downstream of TIR1 to regulate lateral root formation. NAC1 is a transcription activator with an N-terminal NAC domain that binds DNA and a C-terminal activation domain. It activates the expression of two auxin-responsive genes, DBP and AIR3. Transgenic plants with overexpression or antisense NAC1 cDNA show increased or reduced lateral root development, respectively. NAC1 overexpression restores lateral root formation in the auxin-response mutant tir1, indicating that NAC1 acts downstream of TIR1. NAC1 is expressed in root tips, cotyledons, and leaves, and its expression pattern correlates with in situ hybridization results. NAC1 contains a nuclear localization signal and binds to the 35S promoter, suggesting it functions as a transcription factor. NAC1 has a transactivation domain and can dimerize, further supporting its role as a transcription factor. NAC1 overexpression increases plant size and lateral root development, while antisense NAC1 reduces lateral root initiation. NAC1 is involved in the auxin-signaling pathway, as its expression is induced by auxin and it regulates the expression of auxin-responsive genes. NAC1 overexpression promotes lateral root formation, and its expression is required for auxin signaling. NAC1 acts downstream of TIR1 to transmit the auxin signal to the AIR3 gene, promoting lateral root development. NAC1 is a novel transcription factor unique to plants and plays a key role in root development. The study identifies NAC1 as a new regulatory factor in the auxin-signaling pathway that activates genes involved in lateral root specification and initiation. Further studies are needed to fully understand the role of NAC1 in plant development.NAC1 is a NAC family gene that mediates auxin signaling to promote lateral root development in Arabidopsis. The study shows that NAC1 is induced by auxin and acts downstream of TIR1 to regulate lateral root formation. NAC1 is a transcription activator with an N-terminal NAC domain that binds DNA and a C-terminal activation domain. It activates the expression of two auxin-responsive genes, DBP and AIR3. Transgenic plants with overexpression or antisense NAC1 cDNA show increased or reduced lateral root development, respectively. NAC1 overexpression restores lateral root formation in the auxin-response mutant tir1, indicating that NAC1 acts downstream of TIR1. NAC1 is expressed in root tips, cotyledons, and leaves, and its expression pattern correlates with in situ hybridization results. NAC1 contains a nuclear localization signal and binds to the 35S promoter, suggesting it functions as a transcription factor. NAC1 has a transactivation domain and can dimerize, further supporting its role as a transcription factor. NAC1 overexpression increases plant size and lateral root development, while antisense NAC1 reduces lateral root initiation. NAC1 is involved in the auxin-signaling pathway, as its expression is induced by auxin and it regulates the expression of auxin-responsive genes. NAC1 overexpression promotes lateral root formation, and its expression is required for auxin signaling. NAC1 acts downstream of TIR1 to transmit the auxin signal to the AIR3 gene, promoting lateral root development. NAC1 is a novel transcription factor unique to plants and plays a key role in root development. The study identifies NAC1 as a new regulatory factor in the auxin-signaling pathway that activates genes involved in lateral root specification and initiation. Further studies are needed to fully understand the role of NAC1 in plant development.