A Root-Derived Hormone, Strigolactone, Is Involved in the Suppression of Branching in Shoots
Evidence for a root-derived signaling molecule that is involved in the suppression of branching in the shoot comes from grafting studies in mutants with highly branched phenotypes. The branching genes MAX4 (MORE AXILLARY BRANCHING4), RMS1 (RAMOSUS1), and HTD (HIGH-TILLERING DWARF) in Arabidopsis, pea, and rice, respectively, are involved in the production of this root-derived signal, which was found to be a carotenoid derivative (Sorefan et al. 2003; Foo et al. 2005). Recent work has identified this signal as a novel plant hormone, strigolactone, which also promotes the germination of root parasitic weeds and the symbiosis with arbuscular mycorrhizal fungi (Gomez-Roldan et al. 2008; Umehara et al. 2008).