Elucidating the origin and mechanism of a non-canonical auxin signalling pathway in lateral organ development

Ang, Chun Hou (2024) Elucidating the origin and mechanism of a non-canonical auxin signalling pathway in lateral organ development. Doctoral thesis, University of East Anglia.

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The development of complex body plans in multicellular life from a single pluripotent cell necessitates mechanisms that regulate cell differentiation and tissue patterning. The phytohormone auxin plays an important role in almost every aspect of plant growth and development. While the perception and downstream signalling of auxin has been mainly attributed to a canonical degradation-based pathway, numerous alternative pathways have been described in recent years. One such pathway involves a direct auxin-induced switch in the transcriptional regulatory activity of the Auxin Response Factor (ARF) ETTIN (ETT/ARF3). ETT has a middle region domain that contains motifs associated with direct auxin binding and lacks a conserved Cterminus domain involved in canonical pathway interactions. As the ETT clade only exists in the angiosperms, it remains unknown when the pathway evolved. This thesis reports a two-step origin of the ETT clade and its neofunctionalisation through the gain of auxin perception for the role of gynoecium patterning. Phylogenetic analyses confirmed that ETT and its paralogue ARF4 diverged from an ancestral euphyllophyte ETT/ARF4-like clade in the angiosperms and that these paralogues have diverged in motif sequence and domain structure. Auxin sensitivity was identified as an ETT-specific innovation that likely originated in the last common angiosperm ancestor. Importantly, it was found that the DNA-binding domain of ETT influenced auxin sensing, implicating the complex nature of auxin binding by ETT. Furthermore, in planta complementation experiments demonstrated the full genetic redundancy of ETT and ARF4 in leaf and ovary patterning, but a specialised role for the ETT-mediated auxin signalling pathway in style development. Together, this thesis supports the hypothesis that ETT was recruited from an ancestral leaf development role and has undergone neofunctionalisation through the acquisition of direct auxin sensing for a novel role in gynoecium patterning.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Nicola Veasy
Date Deposited: 28 May 2024 14:17
Last Modified: 28 May 2024 14:17
URI: https://ueaeprints.uea.ac.uk/id/eprint/95320


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