How does nitrogen shape plant architecture

Plant nitrogen (N) acquired mainly in forms of nitrate and ammonium from soil dominates growth and development, and high-yield crop production relies heavily on N fertilization. The mechanisms of root adaptation to altered supply of N forms and concentrations have been well characterized and reviewed, while reports concerning effects of N on the architecture of vegetative and reproductive organs are limited and are widely dispersed in the literature. In this review, we summarize the nitrate and amino acid regulation of shoot branching, flowering and panicle development, as well as the N regulation of cell division and expansion in shaping the plant architecture mainly in cereal crops. The basic regulatory steps involving the N supply to control the plant architecture are auxin-, cytokinin-, and strigolactone-controlled cell division in shoot apical meristem and gibberellin-controlled inverse regulation of shoot height and tillering. In addition, transport of amino acids has been shown to be involved in control of shoot branching. The N supply may alter the time and duration of the transition from vegetative to reproductive growth phases, which may in turn affect cereal crop architecture, particularly the structure of panicles for grain yield. Thus, properly manipulating N-regulated architecture can increase the crop yield and N use efficiency.