Patterning the axis in plants--auxin in control.

Axis formation and patterning are fundamental processes establishing the body organization of multicellular organisms. In plants, patterning is not confined to embryogenesis but continues to produce new structures--lateral organs--along the growing primary body axis and also initiates secondary body axes. The signalling molecule auxin has been identified as a key player in plant axial patterning. The shoot and root sections of the axis seem to produce lateral organs in different ways. However, very recent findings suggest a general mechanism of branching triggered by local accumulation of auxin in a 'zone of competence' at the margin of stem-cell systems. How the general auxin signal is converted into organ-specific developmental programs remains a major challenge for the future.