The present PhD thesis dissertation reports new insights for the Brassinosteroids (BRs), and Reactive Oxygen Species (ROS) signaling crosstalk to ensure the plant adaptation to stress in Arabidopsis thaliana and an evolutionary perspective for WOX family of transcription factors in regulating the meristem of the bryophyte Marchantia polymorpha. _x000D_
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Steroid plant hormones, called BRs, control overall growth and development, showing a key role in adaptation to the changing environments. BRs are perceived by Brassinosteroid Insensitive 1 (BRI1)-like family, in which BRI1 is the most characterized receptor. There are two BRI1-like homologues, BRL1 and BRL3, known to be able to recognize Brassinolide (BL) and trigger the BR-mediated cascade; both expressed in the stem cell niche and vasculature. BRL3 mediated signaling has been strongly related to abiotic stress responses, such as thermomorphogenesis, osmotic and drought stress. Our proteomic and transcriptomic analyses reveal a role for BRL3 in ROS signaling, finding Respiratory Oxidase Homologue D (RBOHD), the most studied protein producing ROS in the apoplast, in the BRL3 complex. This interaction points to a direct relation between BR and ROS signaling pathways, focusing specifically on the receptor level. Here, with the use of interdisciplinary methodologies, such as genetics, molecular biology, biochemistry, imaging and physiology, we have uncovered how BR and ROS signaling pathways combine in a synergistic manner to ensure plant development and adaptation. In particular, the work collected in this thesis deciphers the regulation behind the BR and ROS signaling pathways, by specifically studying how the BR receptor BRL3 regulates RBOHD in a transcriptional and posttranslational manner. Moreover, biochemical analyses have revealed the mechanism behind BRL3-RBOHD complex, indicating a constitutive interaction, and is crucial role in BR-mediated ROS in the Arabidopsis root. Additionally, cell biology and physiological approaches suggest the pivotal role of RBOHD protein in the BRI1 and BRL3 receptors stability and, as consequence, mediated traits in plant development and abiotic stress responses. Our results support the model of BRI1 governing the overall plant growth, whereas BRL3 governs stress response, and the requirement of RBOHD-mediated ROS in both complexes to ensure the signal transduction. _x000D_
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On the other hand, through an evolutionary developmental approach, we have uncovered the conservative function of WOX homologue member, MpWOX, in Marchantia polymorpha in the context of controlling the meristem dynamics. MpWOX showed an enriched expression in the area surrounding the apical notch in the thallus, specifically in the ventral zone. Moreover, taking advantage of imaging and bioinformatic tools, the role of this transcription factor in the actively dividing area of the meristem was analyzed in detail, suggesting its relevance in the meristem dynamics. _x000D_
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Overall, the present PhD thesis elucidates how specific components ensure the plant development and adaptation. Specifically, we have added a new layer in the cell-specific steroid receptor BRL3 mediated signaling, by describing its interaction and mechanism with RBOHD. Another key contribution of this thesis has been to delve into the evolutionary mechanisms governing plant meristems, which are crucial for maintaining the integrity of the organism. This _x000D_
work provides novel insights and opens multiple lines of research to uncover how precisely localized components can trigger signaling cascades that govern overall plant development.
| Date of Award | 7 Nov 2025 |
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| Original language | English |
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| Awarding Institution | - Universitat Autònoma de Barcelona (UAB)
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| Supervisor | Ana Isabel Caño Delgado (Director) |
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