Plant & Animal Genomes XVI Conference Plant & Animal Genomes XVI ConferenceJanuary 12-16, 2008
Town & Country Convention Center
San Diego, CA
Axillary bud activity is inhibited by apically-derived auxin moving in the main stem. However, this auxin acts indirectly, without entering the bud. There appear to be at least two mechanisms by which auxin in the main stem can inhibit axillary bud activation. One involves regulation of cytokinin production, and the second involves competition between the primary apex and axillary buds for auxin transport capacity in the main stem. This latter mechanism is the point of action of the Arabidopsis MAX pathway, which is currently defined by 4 loci called MAX1-MAX4, mutation in which results in increased shoot branching. Grafting studies have demonstrated that three of these genes, MAX1, MAX3 and MAX4, are involved in the production of a long-range graft transmissible signal that inhibits bud activity, while the third acts locally in the transduction of this signal, and this is consistent with the molecular identities of these genes. The pathway appears to act by modulating auxin transport capacity in the main stem. Thus bud activity is modulated by a network of interacting hormonal signals, and our progess in understanding this network will be reported. Interestingly, all of these hormones could, at least in theory, act primarily outside the bud. It is therefore of interest to ask whether studies of bud activity should include stems.