Abstract
Strigolactones are root terpenoids capable of acting as a host-derived signal in the rhizosphere communication of plants with arbuscular mycorrhizal (AM) fungi and root parasitic weeds as well as an endogenous plant hormone regulating shoot branching in plants. To obtain insight into the structural requirements of strigolactones for induction of hyphal branching in AM fungi, we performed extensive structure-activity relationship studies using natural strigolactones and their synthetic derivatives. It was found that structural features such as the absolute stereochemistry at C-2' of the D ring and modification of the tricyclic ring substituents significantly affect hyphal branching activity as reported for stimulation of weeds seed germination. However, in contrast to weeds seed germination, the enol ether bond connecting the C and D rings was found not to be essential for hyphal branching, suggesting that the mechanism of strigolactone perception differs between AM fungi and root parasitic weeds.
