Plant Competition: Light Signals Control Polar Auxin Transport

Abstract

Plants typically grow at high densities in natural vegetations and agricultural fields, where they interact with their neighbours to compete for limited resources, and respond with morphological acclimations that facilitate resource capture. A well-studied example of aboveground responses to neighbours is the shade avoidance syndrome (SAS), which is comprised of enhanced stem and petiole elongation, upward leaf movement, apical dominance and early flowering. SAS is induced upon detection of neighbouring vegetation and the earliest signals to exist are a reduction of the red:far-red light ratio (R:FR), caused by far-red light reflection by neighbouring plants. Plants sense this reduced R:FR through their phytochrome photoreceptors which regulate a signal transduction cascade that induces shade avoidance. A key target of this cascade is the biosynthesis and transport of the plant hormone auxin. It is reviewed here how photoreceptors control auxin biosynthesis and auxin transport to promote shade avoidance and fitness of plants in dense stands.