Low-Phosphate Induction of Plastidal Stromules Is Dependent on Strigolactones But Not on the Canonical Strigolactone Signaling Component MAX2

Stromules are highly dynamic protrusions of the plastids in plants. Several factors, such as drought and light conditions, influence the stromule frequency (SF) in a positive or negative way. A relatively recently discovered class of plant hormones are the strigolactones; strigolactones inhibit branching of the shoots and promote beneficial interactions between roots and arbuscular mycorrhizal fungi. Here, we investigate the link between the formation of stromules and strigolactones. This research shows a strong link between strigolactones and the formation of stromules: SF correlates with strigolactone levels in the wild type and strigolactone mutants (max2-1 max3-9), and SF is stimulated by strigolactone GR24 and reduced by strigolactone inhibitor D2.