PhD thesis defense: Shiv Mani Dubey
od 13:30 do 16:00
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Unraveling the Enigmatic World of Auxin Signalling: Subcellular and Tissue- Specific Aspects in the Root of Arabidopsis thaliana
Shiv Mani Dubey, M.Sc.
It is possible to follow the defense online: https://meet.google.com/bkj-pyph-ugc
In this dissertation, my main focus was to advance our understanding of how the plant hormone auxin regulates root growth at the sub-cellular and tissue levels in Arabidopsis thaliana. Auxin controls gene transcription through the SCFTIR1/AFB - Aux/IAA coreceptor complex. Among the TIR1/AFBs auxin receptor family members, TIR1 is strictly localized in the nucleus, while AFB1 is particularly abundant in the cytoplasm but also present in the nucleus. I confirmed the dominant role of AFB1 in controlling rapid auxin responses, such as calcium ion influx, apoplastic alkalinization and rapid root growth inhibition; processes associated with root gravitropism. I discovered a novel AFB1-dependent cytoplasmic auxin perception, and I identified the N-terminal domains of AFB1 and TIR1 crucial in determining their subcellular localization. Furthermore, my research contributed to the discovery that the root surface pH gradient on the root's longitudinal axis is not only regulated by AHA H+ -ATPases, but instead, the rapid auxin response module, comprising the AUX1 auxin influx carrier, AFB1, and the CNCG14 calcium channel, controls the apoplastic pH in the root transition zone. Further, I participated in the discovery of a deeply evolutionarily conserved rapid auxin response pathway that involves the RAF-like kinase, which mediates a wide range of ultra-fast auxin-dependent protein phosphorylation events. Finally, I focused on the cell type-specific auxin responses that govern root growth and development. To overcome previous limitations, I employed the orthogonal ccvTIR1-cvxIAA receptor-ligand pair to manipulate auxin perception and signaling in individual cell-types. I found that primary root growth results from a combination of growth promotion and inhibition, and I addressed the cellautonomous and cell non-autonomous nature of auxin effects on root zonation. My findings shed light on the complex role of individual cell types in regulating root development via auxin signaling. Overall, this dissertation offers valuable insights into auxin signaling at both the subcellular and tissue levels, significantly advancing our understanding of how auxin regulates root growth and development.