How plants recognize pathogens: the science behind LUMINUS® technology

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New phytosanitary strategies have focused on increasing the plants' own defense capacity, making management less dependent on direct action against pathogens. In this scenario, elicitors are gaining increasing prominence. These compounds act by stimulating natural defense mechanisms and putting the plant on alert even before an infection takes hold, representing an important advance for integrated disease management.

Plants possess a sophisticated immune system, built over millions of years of coexistence with microorganisms. This system is capable of recognizing signals associated with the presence of pathogens or damage to the plant's own tissues, triggering coordinated defense responses. Among these mechanisms, pattern recognition immunity (PTI) stands out, activated when receptors present in the cell membrane identify conserved molecules of microorganisms, such as fragments of bacterial flagellin or fungal chitin. Furthermore, plants can also recognize molecules produced by pathogens during the infection process, activating more specific and intense responses known as effector-triggered immunity (ETI).

Once the defense system is activated, a rapid cascade of cell signaling occurs, involving increased intracellular calcium levels, activation of protein kinases (MAPKs), and controlled production of reactive oxygen species (ROS). These signals promote the expression of defense-related genes, resulting in cell wall reinforcement, callose deposition, and the synthesis of antimicrobial compounds such as phytoalexins. Together, these responses increase the plant's ability to resist the establishment and progression of diseases.

LUMINUS® and the flg22 peptide: a signal that the plant recognizes.

Among the most recent technologies aimed at activating plant defenses is LUMINUS®, the first commercially registered product in Brazil formulated with the flg22 peptide. This peptide, composed of 22 amino acids and derived from bacterial flagellin, is recognized by plants as a signal associated with the presence of microorganisms.

Following foliar application, flg22 is detected by the Flagellin-Sensing 2 (FLS2) receptor, located in the plasma membrane of plant cells. This recognition triggers one of the best-characterized pathways of plant immunity, initiating a rapid cascade of intracellular signaling.

Activation of FLS2 promotes the formation of a complex with co-receptors, amplifying the defense signal. As a consequence, there is an increase in cytoplasmic calcium levels, activation of protein kinases, controlled production of reactive oxygen species (ROS), and regulation of genes involved in the synthesis of hormones, phytoalexins, and other components related to plant defense.

In practice, flg22 acts as an early warning signal, preparing the plant to respond more quickly and efficiently to a biotic challenge, a phenomenon that underlies the establishment of the state of physiological readiness known as "priming" (Figure 1).

Biochemical evidence of the state of readiness induced by LUMINUS®

With the aim of understanding the biochemical changes associated with the application of LUMINUS®, a study was conducted with soybean plants, carried out by Metabolic Biosolutions and PDPA/UFRRJ, in partnership with UPL. The analysis allowed the identification of changes in proteins related to different physiological processes involved in the plant immune response.

Consistent with the expected mechanism of action for flg22, the identified proteins were associated with signal perception and transduction processes, regulation of cellular metabolism, maintenance of redox homeostasis, and activation of defense responses. These results reinforce the evidence that recognition of flg22 by the FLS2 receptor triggers a complex signaling network, involving changes in cytoplasmic Ca²⁺ levels, activation of MAPK cascades, production and control of reactive oxygen species (ROS), regulation of gene expression, and synthesis of defense-related metabolites. Together, these responses promote a broad biochemical reprogramming of the plant, allowing the initial signals of elicitor perception to be converted into effective protective mechanisms.

In addition to the changes observed in the initial stages of the response, some proteins remained differentially accumulated for up to 15 days after the application of LUMINUS®. Considering that the classic events of ITP are triggered soon after the perception of the elicitor, the persistence of these changes suggests that the initial activation of immunity results in lasting metabolic adjustments. Thus, the proteins identified in this later period constitute evidence that the application of LUMINUS® not only activates immediate defense mechanisms, but also contributes to the establishment of a biochemical memory capable of favoring faster and more efficient responses to future challenges.

Among these proteins, 9-lipoxygenase (9-LOX) stood out, an enzyme involved in the biosynthesis of oxylipins, signaling molecules associated with tissue communication and the coordination of defense responses. In soybeans, LOX-type enzymes are strongly associated with basal resistance and defense memory, and their presence in the results indicates that LUMINUS® sustained long-lasting lipid protection in the plant (Table 1).

A higher abundance of myo-inositol-1-phosphate synthase (MIPS), a key enzyme in the biosynthesis of myo-inositol and its derivatives, was also observed. These compounds participate in cell signaling processes, regulation of intracellular calcium, and response to biotic and abiotic stresses. Their identification indicates that plants treated with LUMINUS® maintain greater readiness to trigger this signaling, with more stable membranes and an enhanced capacity for rapid reactivation of defenses (Table 1).

Complementing this set of responses, a greater abundance of leghemoglobin reductase, a protein associated with maintaining cellular redox balance, was identified. After PTI activation, the increase in ROS and nitric oxide is an essential part of the signaling, but this process needs to be regulated to avoid damaging the plant itself. The presence of this enzyme shows that LUMINUS® also contributes to the fine-tuning of this response, ensuring efficiency without compromising cellular integrity (Table 1).

Taken together, the study demonstrated that plants treated with LUMINUS® mobilized mechanisms capable of sustaining the defense response without impairing their normal functioning. The product not only triggers immediate mechanisms but also promotes a long-term metabolic condition that keeps the crop alert, ready to respond more efficiently to the occurrence of pathogens.

LUMINUS® results in the field (UPL)

The results presented in Figure 2 demonstrate that the inclusion of LUMINUS® (flg22) in the management program provided a significant reduction in the severity of the soybean foliar disease complex, composed of Septoria glycones, cercospora spp. And Corynespora cassiicola, in different locations. These results indicate that the early activation of plant defense mechanisms through the flg22 peptide enhances the efficiency of phytosanitary management, favoring the establishment of the "priming" state and allowing for faster and more intense responses to pathogen pressure.

Camila Ferreira de Pinho,
Eduardo de Souza Amorim,
Anthony Côrtes Gomes,
UFRRJ;
Gabriela de Souza da Silva,
Rita de Cássia Silva,
Metabolic Biosolutions;
Diego Costa,
R&D Manager for Biocontrol and Plant Nutrition;
Mariana Yama,
Strategic Marketing Manager Brazil - Biocontrol