AXR1 acts after lateral bud formation to inhibit lateral bud growth in Arabidopsis

The AXR1 gene of Arabidopsis is required for many auxin responses. The high ly branched shoot phenotype of mature axr1 mutant plants has been taken as genetic evidence for a role of auxin in the control of shoot branching. We compared the development of lateral shoots in wild-type Columbia and axr1-1 2 plants. In the wild type, the pattern of lateral shoot development depend s on the developmental stage of the plant. During prolonged vegetative grow th, axillary shoots arise and develop in a basal-apical sequence. After flo ral transition, axillary shoots arise rapidly along the primary shoot axis and grow out to form lateral inflorescences in an apical-basal sequence. Fo r both patterns, the axr1 mutation does not affect the timing of axillary m eristem formation; however, subsequent lateral shoot development proceeds m ore rapidly in axr1 plants. The outgrowth of lateral inflorescences from ex cised cauline nodes of wild-type plants is inhibited by apical auxin. axr1- 12 nodes are resistant to this inhibition. These results provide evidence f or common control of axillary growth in both patterns, and suggest a role f or auxin during the late stages of axillary shoot development following the formation of the axillary bud and several axillary leaf primordia.