An auxin-dependent distal organizer of pattern and polarity in the Arabidopsis root

Root formation in plants involves the continuous interpretation of position al cues. Physiological studies have linked root formation to auxins. An aux in response element displays a maximum in the Arabidopsis root and we inves tigate its developmental significance. Auxin response mutants reduce the ma ximum or its perception, and interfere with distal root patterning. Polar a uxin transport mutants affect its localization and distal pattern. Polar au xin transport inhibitors cause dramatic relocalization of the maximum, and associated changes in pattern and polarity. Auxin application and laser abl ations correlate root pattern with a maximum adjacent to the vascular bundl e. Our data indicate that an auxin maximum at a vascular boundary establish es a distal organizer in the root.