Abstract

Summary In plants, the plasticity of root architecture in response to nitrogen availability largely determines nitrogen acquisition efficiency. One poorly understood root growth response to low nitrogen availability is an observed increase in the number and length of lateral roots ( LR s). Here, we show that low nitrogen‐induced A rabidopsis LR growth depends on the function of the auxin biosynthesis gene TAR 2 (tryptophan aminotransferase related 2). TAR 2 was expressed in the pericycle and the vasculature of the mature root zone near the root tip, and was induced under low nitrogen conditions. In wild type plants, low nitrogen stimulated auxin accumulation in the non‐emerged LR primordia with more than three cell layers and LR emergence. Conversely, these low nitrogen‐mediated auxin accumulation and root growth responses were impaired in the tar2‐c null mutant. Overexpression of TAR 2 increased LR numbers under both high and low nitrogen conditions. Our results suggested that TAR 2 is required for reprogramming root architecture in response to low nitrogen conditions. This finding suggests a new strategy for improving nitrogen use efficiency through the engineering of TAR 2 expression in roots.