Thesis defense: Pauline Savourat
Hydathode
development
leaf
guttation
Thursday, December 11 2025 2 pm - INRAE, Versailles
Genetic and Cellular Basis of Hydathode Development and their Physiology
Hydathodes are specialized structures found in vascular plants and are known for their role in guttation, a process by which droplets of xylem sap-derived fluids are exuded from leaves when root pressure exceeds the transpiration rate of leaves. The hydathodes of Arabidopsis are located at the apex and at each tooth of the leaf. Morphologically, they are composed of three major elements: tracheids, which irrigate the epithem, a specialized tissue composed of small cells that allows remobilization of nutrients that have not been used by the leaf, as well as open pores that resemble huge stomata. Because this organ connects the plant vasculature to the external environment, it is an entry site for vascular pathogens. Despite morphological and physiological studies carried out on these structures in different plant species, the molecular and cellular mechanisms governing their development remain poorly explored. Using various genetic, microscopic and transcriptomic approaches, we demonstrate that hydathodes are formed in two successive stages: a specification phase, followed by a division and differentiation phase. We clarify the role of auxin in this process, showing that this hormone, as well as the molecular regulators involved in its local accumulation (CUP-SHAPED COTYLEDON, CUC; DORNRÖSHEN-LIKE, DRNL; STYLISH, STY and YUCCA, YUC), are essential for hydathode specification. Moreover, we show that hydathode development can be uncoupled from tooth formation. Further development relies on maintaining cell division and repressing endoreduplication in the epithem, a step modulated by cytokinin and auxin. At the contrary, the development of water pores could be the result of a shorter proliferative phase. This study has provided genetic tools for studying the impact of hydathodes on plant physiology, and we use it to demonstrate that hydathodes are necessary for water management in the leaf. Altogether, this work proposes a model of hydathode development and the acquisition of its functions.
Director: Patrick Laufs, "Transcription Factors and Architecture" FTA team, INRAE, IJPB, Versailles
Jury members
> Soazig Guyomarc'h (Rapportrice) - Université de Montpellier, DIADE, CERES
> Yohan Coudert, (Rapporteur) - CNRS, ENS Lyon, RDP, SIGNAL, Lyon
> Marie Monniaux (Examinatrice) - CNRS, Université de Lille, EEP, Villeneuve d’Ascq
> Anja Krieger-Liszkay (Examinatrice) - CNRS, Université Paris-Saclay, I2BC, Photobiology, Photosynthesis, Photocatalysis, Gif-sur-Yvette
> Hannes Kollist (Examinateur) - INRAE, IPS2, STRESS, Gif-sur-Yvette
Research developed at the Institute Jean-Pierre Bourgin for Plant Sciences.
Hydathodes are specialized structures found in vascular plants and are known for their role in guttation, a process by which droplets of xylem sap-derived fluids are exuded from leaves when root pressure exceeds the transpiration rate of leaves. The hydathodes of Arabidopsis are located at the apex and at each tooth of the leaf. Morphologically, they are composed of three major elements: tracheids, which irrigate the epithem, a specialized tissue composed of small cells that allows remobilization of nutrients that have not been used by the leaf, as well as open pores that resemble huge stomata. Because this organ connects the plant vasculature to the external environment, it is an entry site for vascular pathogens. Despite morphological and physiological studies carried out on these structures in different plant species, the molecular and cellular mechanisms governing their development remain poorly explored. Using various genetic, microscopic and transcriptomic approaches, we demonstrate that hydathodes are formed in two successive stages: a specification phase, followed by a division and differentiation phase. We clarify the role of auxin in this process, showing that this hormone, as well as the molecular regulators involved in its local accumulation (CUP-SHAPED COTYLEDON, CUC; DORNRÖSHEN-LIKE, DRNL; STYLISH, STY and YUCCA, YUC), are essential for hydathode specification. Moreover, we show that hydathode development can be uncoupled from tooth formation. Further development relies on maintaining cell division and repressing endoreduplication in the epithem, a step modulated by cytokinin and auxin. At the contrary, the development of water pores could be the result of a shorter proliferative phase. This study has provided genetic tools for studying the impact of hydathodes on plant physiology, and we use it to demonstrate that hydathodes are necessary for water management in the leaf. Altogether, this work proposes a model of hydathode development and the acquisition of its functions.
Director: Patrick Laufs, "Transcription Factors and Architecture" FTA team, INRAE, IJPB, Versailles
Jury members
> Soazig Guyomarc'h (Rapportrice) - Université de Montpellier, DIADE, CERES
> Yohan Coudert, (Rapporteur) - CNRS, ENS Lyon, RDP, SIGNAL, Lyon
> Marie Monniaux (Examinatrice) - CNRS, Université de Lille, EEP, Villeneuve d’Ascq
> Anja Krieger-Liszkay (Examinatrice) - CNRS, Université Paris-Saclay, I2BC, Photobiology, Photosynthesis, Photocatalysis, Gif-sur-Yvette
> Hannes Kollist (Examinateur) - INRAE, IPS2, STRESS, Gif-sur-Yvette
Research developed at the Institute Jean-Pierre Bourgin for Plant Sciences.
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