Physcomitrella patens MAX2 characterization suggests an ancient role for this F-box protein in photomorphogenesis rather than strigolactone signalling

New Phytol. 2018 Jul;219(2):743-756. doi: 10.1111/nph.15214. Epub 2018 May 21.


Strigolactones (SLs) are key hormonal regulators of flowering plant development and are widely distributed amongst streptophytes. In Arabidopsis, SLs signal via the F-box protein MORE AXILLARY GROWTH2 (MAX2), affecting multiple aspects of development including shoot branching, root architecture and drought tolerance. Previous characterization of a Physcomitrella patens moss mutant with defective SL synthesis supports an ancient role for SLs in land plants, but the origin and evolution of signalling pathway components are unknown. Here we investigate the function of a moss homologue of MAX2, PpMAX2, and characterize its role in SL signalling pathway evolution by genetic analysis. We report that the moss Ppmax2 mutant shows very distinct phenotypes from the moss SL-deficient mutant. In addition, the Ppmax2 mutant remains sensitive to SLs, showing a clear transcriptional SL response in dark conditions, and the response to red light is also altered. These data suggest divergent evolutionary trajectories for SL signalling pathway evolution in mosses and vascular plants. In P. patens, the primary roles for MAX2 are in photomorphogenesis and moss early development rather than in SL response, which may require other, as yet unidentified, factors.

Keywords: F-box protein; bryophyte; hormone signalling; moss; photomorphogenesis; strigolactone.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bryopsida / genetics
  • Bryopsida / metabolism*
  • Bryopsida / radiation effects
  • Cell Nucleus / drug effects
  • Cell Nucleus / metabolism
  • Cell Nucleus / radiation effects
  • Epistasis, Genetic / drug effects
  • Epistasis, Genetic / radiation effects
  • F-Box Proteins / genetics
  • F-Box Proteins / metabolism*
  • Gene Expression Regulation, Plant / drug effects
  • Gene Expression Regulation, Plant / radiation effects
  • Lactones / metabolism*
  • Lactones / pharmacology
  • Light*
  • Models, Biological
  • Morphogenesis / drug effects
  • Morphogenesis / radiation effects*
  • Mutation / genetics
  • Phenotype
  • Plant Proteins / genetics
  • Plant Proteins / metabolism*
  • Protein Transport / drug effects
  • Protein Transport / radiation effects
  • Sequence Homology, Amino Acid
  • Signal Transduction*
  • Transcription, Genetic / drug effects
  • Transcription, Genetic / radiation effects


  • F-Box Proteins
  • GR24 compound
  • Lactones
  • Plant Proteins