ASSESSING THE IMPACT OF RHAMNOLIPIDS ON SOYBEAN NODULATION AND NITROGEN FIXATION

KOURDOVA, LUCILLE TIHOMIROVA; ALVARADO VAAMONDE, LOURDES; LESCANO, IGNACIO; FABRO, GEORGINA; LASCANO, RAMIRO

Buzios

Simposio; Simposio brasileiro de genética molecular de plantas; 2025

Sociedad Brasilera de Genética

Legumes form symbiotic relationships with rhizobacteria that fix atmospheric nitrogen through the development of root nodules. These interactions activate systemic responses that enhance tolerance to various biotic and abiotic stresses. Induced systemic resistance (ISR), promoted by plant growth-promoting bacteria, strengthens the symbiosis between legumes and rhizobia, which in turn reinforces ISR. This suggests that the combination of symbiosis and defense induction by microorganisms or their derived molecules may have positive additive effects.Rhamnolipids (RLs) are glycolipids with antibacterial and antifungal properties that can trigger the innate immune system of plants. Their ecological benefits, such as low toxicity and biodegradability, make them attractive for sustainable agribusiness practices. It has been proposed that RLs play a role in bacterial communication (quorum sensing), a key mechanism for colonization and nodulation establishment. In this context, we propose that RLs may enhance the interaction between soybean and rhizobia, improving beneficial effects and overall plant physiological status.To investigate this hypothesis, in vitro and in planta experiments were conducted using different RLs concentrations. The effect of RLs on the growth and inhibition of the rhizobium Bradyrhizobium diazoefficiens (Bd) was evaluated by in vitro experiments. For the late nodulation stage, soybean seeds treated with RLs were transferred to a hydroponic culture with Bd, and growth parameters (root length and weight, shoot length, leaf area, nodule number and weight) and photosynthetic activity (CO₂ assimilation, PSII efficiency) were assessed at 21 days post inoculation. Additionally, nitrogen assimilation was analyzed by measuring ureide content in nodules, leaves, and phloem. Among the parameters evaluated, a significant difference was observed only in ureide content. While the ureide content in leaves increased, it decreased in nodules, suggesting an enhanced nitrogen flux between the nodules and the aerial part of the plant. This shift could potentially lead to improved growth, higher yields, or greater tolerance to adverse conditions, such as abiotic stress.Additionally, we will present results on the influence of RLs on early nodulation and initial interactions with Bd, including root hair deformation and infection thread formation.Biotechnological strategies based on RLs could optimize nitrogen fixation efficiency, reduce dependence on synthetic fertilizers, and enhance plant resilience to biotic and abiotic stresses. This approach offers an innovative and sustainable agricultural strategy, leveraging natural compounds to improve crop productivity while minimizing environmental impact.