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Rôle des strigolactones dans le développement de l’architecture aérienne de la plante en interaction avec les autres hormones végétales

Abstract : The different processes of plant growth and development are under the influence of growth regulators which interact in complex hormonal networks and feedback mechanisms. The control of shoot branching involves 3 key plant hormones, auxin, cytokinins (CKs) and strigolactones (SLs). Auxin and SLs repress axillary bud outgrowth whereas CKs stimulate it. Different mechanisms of interactions between these signals have already been suggested in controlling shoot branching. Auxin controls SLs and CKs levels, and SLs and CKs pathways converge on the same target, the TCP transcription factor BRC1 in the axillary bud. In pea, the high shoot branching of ramosus (rms) mutants are known for being impaired in the SLs pathway. RMS1 (PsMAX4) and RMS5 (PsMAX3) genes are involved in SL biosynthesis while RMS3 (PsD14) (receptor) and RMS4 (PsMAX2) are involved in SL perception. In addition to sharing their high branching phenotype, the rms mutants display a dwarf phenotype. However the role of SLs in controlling plant height was unknown. Here we show that SLs control internode length by acting on cell division in a Gibberellin-independent way.The rms mutants show similar physiological characteristics: high expression of the SL-biosynthesis genes and very low xylem-sap CKs (X-CKs) content. In contrast, the rms2 mutant with similar shoot phenotype shows very low expression of SL-biosynthesis genes and high X-CKs content. Previous studies suggested that rms2 was affected in a shoot-to-root feedback signal controlling both SL biosynthesis and X-CKs level. Whether this feedback signal was auxin or not was highly discussed. Here we demonstrated that the RMS2 gene is the pea homologue of the Arabidopsis AFB4/5 gene, encoding an F-box protein which belongs to the TIR1/AFB (Auxin signaling F-Box) auxin receptor family. This suggests that the RMS2-dependent feedback signal is very likely auxin. Moreover our results suggest a role for SLs in the repression of auxin content in pea stem via the regulation of auxin metabolism gene expression. These results highlighted that for the control of shoot branching, interactions between auxin and strigolactones involve multiple mechanisms leading to regulation loop where both hormones are able to regulate the biosynthesis of each other.
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Yasmine Ligerot. Rôle des strigolactones dans le développement de l’architecture aérienne de la plante en interaction avec les autres hormones végétales. Biologie végétale. Université Paris Saclay (COmUE), 2015. Français. ⟨NNT : 2015SACLS118⟩. ⟨tel-01655501⟩

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