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Strigolactones regulate shoot branching in land plants: Evolution of the signalling pathway
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Edité par CCSD -
International audience. Strigolactones (SLs) are phytohormones regulating various developmental processes, including shoot branching and root architecture in vascular plants. Exuded in the soil, SLs have been described as host-presence signals for parasitic weeds, inducing their seed germination. SLs also promote hyphal growth of Arbuscular Mycorrhizal fungi, beneficial to plant growth. SLs are found in the extant descendants of early land plants as the moss Physcomitrella patens (P. patens) and even in some charophytes. Great progress has been achieved in deciphering the SL synthesis and signaling pathways in vascular plants, but the evolution of SL pathway remains elusive.To investigate SL pathway evolution, we have undertaken a reverse genetics approach completed with transcriptomic analyses in the bryophyte model P. patens. Knock-Out mutants have been obtained in both CAROTENOID CLEAVAGE DEOXYGENASE 8 (PpCCD8) and MORE AXILLARY GROWTH 2 (PpMAX2) moss genes, which homologs in vascular plants are involved in SL synthesis and signalling respectively. Characterization of the Ppccd8 mutant has shown that SLs control moss filament extension, and branching of leafy shoot. The first steps of hormone synthesis seem similar in non-vascular and vascular plants. In contrast, analysis of Ppmax2 mutant suggests that SL signalling is more divergent. Furthermore, there is no true ortholog for the SL receptor gene DWARF14 (D14) in the moss genome, but as many as 13 homologs (called PpKAI2-Like genes) are present. We have obtained several multiple mutants in the PpKAI2-Like genes, through CRISPR-Cas9 strategy. These mutants are now being characterized for their response to SLs. In addition, PpKAI2-Like proteins are being expressed for binding assays. Latest results on the project will be presented.
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