Heterogeneous phosphate supply influences maize lateral root proliferation by regulating auxin redistribution.

BACKGROUND AND AIMS: Roots take up phosphorus (P) as inorganic phosphate (Pi). Enhanced root proliferation in Pi-rich patches enables plants to capture the unevenly distributed Pi, but the underlying control of root proliferation remains largely unknown. Here, the role of auxin in this response was investigated in maize (Zea mays). METHODS: A split-root, hydroponics system was employed to investigate root responses to Pi supply, with one (heterogeneous) or both (homogeneous) sides receiving 0 or 500 µm Pi. KEY RESULTS: Maize roots proliferated in Pi-rich media, particularly with heterogeneous Pi supply. The second-order lateral root number was 3-fold greater in roots of plants receiving a heterogeneous Pi supply than in roots of plants with a homogeneous Pi supply. Root proliferation in a heterogeneous Pi supply was inhibited by the auxin transporter inhibitor 1-N-naphthylphthalamic acid (NPA). The proliferation of lateral roots was accompanied by an enhanced auxin response in the apical meristem and vascular tissues at the root tip, as demonstrated in a DR5::RFP marker line. CONCLUSIONS: It is concluded that the response of maize root morphology to a heterogeneous Pi supply is modulated by local signals of Pi availability and systemic signals of plant P nutritional status, and is mediated by auxin redistribution.