Local auxin production underlies a spatially restricted neighbor-detection response in Arabidopsis

Significance Being photoautotrophic, plant growth is exquisitely sensitive to the light environment. In response to light cues from potential competitors, plants initiate a neighbor-proximity response favoring direct access to sunlight. This response includes elevation of the leaf (hyponasty) that is rapidly triggered following perception of neighbors. Light signals emanating from surrounding vegetation are heterogeneous; however, it is unknown how plants trigger a localized response in such conditions. We show that auxin synthesis in the leaf blade coupled with transport into the petiole induces a hyponastic response restricted to the leaf perceiving the signal. Moreover, we identify a branch of auxin signaling controlling petiole elevation while not affecting elongation. Our work uncovers a mechanism underlying plant responses to a heterogeneous environment.