New genes in the strigolactone-related shoot branching pathway.

Shoot branching is controlled by the formation and subsequent outgrowth of axillary buds in the axils of leaves. Axillary buds are indeterminate structures that can be arrested and await endogenous or environmental cues for outgrowth. A major breakthrough in this area of plant development has been the discovery that a specific group of terpenoid lactones, named strigolactones, can directly or indirectly, inhibit axillary bud outgrowth. Since that discovery, new branching mutants have been identified with reduced strigolactone levels or which are defective in strigolactone regulation or response. DWARF27 and DWARF14 probably act on strigolactone biosynthesis and strigolactone metabolism or signal transduction, respectively. Auxin signaling mutants have also been useful in demonstrating that strigolactone levels are mediated by a classical auxin signal transduction pathway. The discovery and characterization of these mutants is an important first step toward understanding the mechanisms of strigolactone biosynthesis and signaling and their importance in regulating shoot branching.