Thesis defense: Justine Broutin
Thursday, February 19 2026 2 pm - INRAE, Versailles
Investigation of the mode of action and the biostimulant effects of a protein hydrolysate on plants
With a continuously growing global population, the agricultural sector faces a major challenge: producing sufficient food while contending with increasingly unfavorable environmental conditions. Furthermore, current public policies mandate a reduction in agricultural inputs in order to mitigate the environmental pollution they generate and to avoid compromising public health. In this context, biostimulants have emerged as a promising strategy to maintain crop yields while reducing the use of mineral fertilizers and limiting the impact of stress conditions. Among these biostimulants, protein hydrolysates (PHs) are already known for their ability to enhance plant growth and yield. However, the mechanisms underlying their effects remain insufficiently understood.
A major objective of this thesis was to characterise the effects of a specific PH, Aminovital Power (AVP), produced by Fertinagro, on the model plant Arabidopsis thaliana and on a cultivated crop species, wheat Triticum aestivum. In vitro, AVP modifies root system architecture in Arabidopsis under nitrogen-replete conditions, indicating a biostimulant rather than a nutritional mode of action. In contrast, in the absence of nitrogen, AVP does not support root growth, confirming that it is not, in itself, a significant source of nutrients. Similarly, AVP modifies both root and shoot growth in wheat cultivated hydroponically or in soil and significantly enhances grain yield. To approximate field-like conditions, experiments performed using the Phenoscope, an automated phenotyping platform providing highly reproducible and controlled conditions, revealed a dose-dependent increase in shoot area and biomass in Arabidopsis. Following the validation of this growth-promoting effect, the subsequent objective was to identify, through multi-omics approaches, the biological, genetic, and metabolic targets of AVP to better understand its mode of action and to support the optimisation of its practical use.
In Arabidopsis, AVP supply affects the expression of numerous genes, including the nitrate transporter NRT2.1 (NITRATE TRANSPORTER 2) and the enzyme NiR (nitrite reductase), both of which show reduced transcript levels. These changes result in decreased nitrate transport and assimilation. Conversely, an enhanced assimilation of amino acids was observed in AVP-treated plants. For instance, amino acid transporters such as LHT1, CAT1, and ProT1, as well as nitrogen-assimilating enzymes including glutamate dehydrogenase (GDH) and glutamate decarboxylase (GAD), are upregulated. The accumulation of a large number of metabolites, among them amino acids such as glutamine, which is present only in trace amounts in AVP, was also detected. This suggests that amino acids contained in AVP are potentially taken up and metabolised by the plant, or alternatively may act as signalling molecules. This amino-acid accumulation is likely responsible for the increased activity of TOR kinase, a central regulator of growth in all eukaryotes.
In conclusion, the results of this thesis reproducibly demonstrated, under controlled conditions, the growth- and yield-promoting effects of a protein hydrolysate. Moreover, AVP application induces extensive changes in gene expression, particularly in genes involved in nitrogen metabolism, as well as in the accumulation of metabolites in treated plants. These findings demonstrate that AVP exerts a significant and broad impact on the biological processes of these plants.
With a continuously growing global population, the agricultural sector faces a major challenge: producing sufficient food while contending with increasingly unfavorable environmental conditions. Furthermore, current public policies mandate a reduction in agricultural inputs in order to mitigate the environmental pollution they generate and to avoid compromising public health. In this context, biostimulants have emerged as a promising strategy to maintain crop yields while reducing the use of mineral fertilizers and limiting the impact of stress conditions. Among these biostimulants, protein hydrolysates (PHs) are already known for their ability to enhance plant growth and yield. However, the mechanisms underlying their effects remain insufficiently understood.
A major objective of this thesis was to characterise the effects of a specific PH, Aminovital Power (AVP), produced by Fertinagro, on the model plant Arabidopsis thaliana and on a cultivated crop species, wheat Triticum aestivum. In vitro, AVP modifies root system architecture in Arabidopsis under nitrogen-replete conditions, indicating a biostimulant rather than a nutritional mode of action. In contrast, in the absence of nitrogen, AVP does not support root growth, confirming that it is not, in itself, a significant source of nutrients. Similarly, AVP modifies both root and shoot growth in wheat cultivated hydroponically or in soil and significantly enhances grain yield. To approximate field-like conditions, experiments performed using the Phenoscope, an automated phenotyping platform providing highly reproducible and controlled conditions, revealed a dose-dependent increase in shoot area and biomass in Arabidopsis. Following the validation of this growth-promoting effect, the subsequent objective was to identify, through multi-omics approaches, the biological, genetic, and metabolic targets of AVP to better understand its mode of action and to support the optimisation of its practical use.
In Arabidopsis, AVP supply affects the expression of numerous genes, including the nitrate transporter NRT2.1 (NITRATE TRANSPORTER 2) and the enzyme NiR (nitrite reductase), both of which show reduced transcript levels. These changes result in decreased nitrate transport and assimilation. Conversely, an enhanced assimilation of amino acids was observed in AVP-treated plants. For instance, amino acid transporters such as LHT1, CAT1, and ProT1, as well as nitrogen-assimilating enzymes including glutamate dehydrogenase (GDH) and glutamate decarboxylase (GAD), are upregulated. The accumulation of a large number of metabolites, among them amino acids such as glutamine, which is present only in trace amounts in AVP, was also detected. This suggests that amino acids contained in AVP are potentially taken up and metabolised by the plant, or alternatively may act as signalling molecules. This amino-acid accumulation is likely responsible for the increased activity of TOR kinase, a central regulator of growth in all eukaryotes.
In conclusion, the results of this thesis reproducibly demonstrated, under controlled conditions, the growth- and yield-promoting effects of a protein hydrolysate. Moreover, AVP application induces extensive changes in gene expression, particularly in genes involved in nitrogen metabolism, as well as in the accumulation of metabolites in treated plants. These findings demonstrate that AVP exerts a significant and broad impact on the biological processes of these plants.
Director: Christian Meyer, "Nitrogen Use, transport and signaling" NUTS team, INRAE, IJPB, Versailles
Co-supervision:
> Anne-Sophie Leprince, "Nitrogen Use, transport and signaling" NUTS team, INRAE, IJPB, Versailles
> Benjamin Ourliac, Fertinagro
Jury members
> Sandrine Rufffel (Rapportrice) - "Institut des Sciences des Plantes de Montpellier" IPSiM, Montpellier
> Phillipe Etienne (Rapporteur) - Université de Caen, "Ecologie végétale, Agronomie & nutrition N,C,S" EVA, "Interactions Nutritionnelles Conduites et Contraintes Abiotiques" INCCA, Caen
> Marianne Delarue (Examinatrice) - Université Paris-Saclay, "Institute of plant Sciences Paris-Saclay"IPS2, Gif-sur-Yvette
> Alain Bouchereau (Examinateur) - Université de Rennes
> Loïc Rajjou (Examinateur) - AgroParisTech, INRAE, IJPB, Versailles
Research developed at the Institute Jean-Pierre Bourgin for Plant Sciences.
Back
