Nitrogen nutrition as versatile determinant of root plasticity

Abstract

Plants adapt root system architecture to the availability of mineral elements. When grown under nitrogen (N)-limiting soils, plants develop longer primary or seminal and lateral roots, but for long time it has remained unclear how this N foraging response is coordinated. By exploiting the natural variation in the root foraging response to mild nitrogen deficiency we employed genome-wide association mapping in Arabidopsis and identified genes involved in brassinosteriod (BR) biosynthesis, BR signaling and auxin biosynthesis. In all three cases, allelic variants modulate not only the extent of root elongation under mild N deficiency but also determine whether primary or lateral roots are preferentially promoted. Currently, de-novo screening in the ‘IPK Phenosphere’ and translational approaches are undertaken to identify allelic variants involved in N-dependent root elongation in barley.

When plant roots grow under localized N supply, it has been observed previously that nitrate stimulates lateral root elongation, while local ammonium promotes lateral root branching. Based on auxin and pH reporters as well as pharmacological approaches and mutant analysis, we found that acidification of the root apoplast after AMT-mediated ammonium uptake drives pH-dependent radial auxin transport to simulate lateral root emergence. In contrast, high ammonium abundance suppresses cell division and elongation via iron-dependent superoxide radical formation, which plants counteract with enhanced vitamin B6 formation. Taken together, these examples show how the balance between systemic and local N signals shape root patterning by addressing distinct steps in the root developmental program.