Bonhomme_2022_J.Exp.Bot__

Strigolactones (SLs), long known as butenolide rhizospheric signals, have been recognised since 2008 as a class of hormones regulating many aspects of plant development. Many authors also anticipate 'KAI2 Ligand' (KL) as a novel class of phytohormones; however, this ligand remains elusive. Core genes of SL and KL pathways, first described in angiosperms, are found in all land plants and some even in green algae. This review reports current knowledge of these pathways in bryophytes. Data about the pathways mostly comes from two models: the moss Physcomitrium patens and the liverwort Marchantia. Gene targeting methods have allowed functional analyses of both models. Recent work in Marchantia suggests that SLs' ancestral role was to recruit beneficial microbes as arbuscular mycorrhizal fungi. By contrast, the SL hormonal role observed in P. patens is likely a result of convergent evolution. Evidence for a functional KL pathway in both bryophyte models is very recent. Nevertheless, many unknowns remain and warrant a more extensive investigation of SL and KL pathways in various land plant lineages.