The development of plant root systems is sensitive to the availability and distribution of nutrients within the soil. For example, lateral roots proliferate preferentially within nitrate (NO3-)-rich soil patches. A NO3--inducible Arabidopsis gene (ANR1), was identified that encodes a member of the MADS box family of transcription factors. Transgenic plants in which ANR1 was repressed had an altered sensitivity to NO3- and no longer responded to NO3--rich zones by lateral root proliferation, indicating that ANR1 is a key determinant of developmental plasticity in Arabidopsis roots.