From spatio-temporal morphogenetic gradients to rhythmic patterning at the shoot apex

A key question in developmental biology is how morphogenetic regulators control patterning. Recent findings have raised an important question: do morphogenetic signals carry information not only in space, as originally proposed in the morphogen concept, but also in time? The hormone auxin is an essential plant morphogenetic regulator that drives rhythmic organogenesis at the shoot apical meristem. Here, we used a quantitative imaging approach to map auxin distribution and response. We demonstrate the existence of high-definition spatio-temporal auxin distribution in the meristem. We provide evidence that developing organs are auxin-emitting centers that could allow self-sustained distribution of auxin through a structured auxin transport network converging on the meristem center. We finally demonstrate that regulation of histone acetylation allows cells to measure the duration of the exposition to auxin preceding organ initiation, providing a remarkable example of how both spatial and temporal morphogenetic information generates rhythmic patterning.