The cell wall (CW) is a dynamic structure extensively remodeled during plant growth and under stress conditions, however little is known about its roles during the immune system priming, especially in crops. In order to shed light on such a process, we used the Phaseolus vulgaris-Pseudomonas syringae (Pph) pathosystem and the immune priming capacity of 2,6-dichloroisonicotinic acid (INA). In the first instance we confirmed that INA-pretreated plants were more resistant to Pph, which was in line with the enhanced production of H₂O₂ of the primed plants after elicitation with the peptide flg22. Thereafter, CWs from plants subjected to the different treatments (non- or Pph-inoculated on non- or INA-pretreated plants) were isolated to study their composition and properties. As a result, the Pph inoculation modified the bean CW to some extent, mostly the pectic component, but the CW was as vulnerable to enzymatic hydrolysis as in the case of non-inoculated plants. By contrast, the INA priming triggered a pronounced CW remodeling, both on the cellulosic and non-cellulosic polysaccharides, and CW proteins, which resulted in a CW that was more resistant to enzymatic hydrolysis. In conclusion, the increased bean resistance against Pph produced by INA priming can be explained, at least partially, by a drastic CW remodeling.

Common bean (Phaseolus vulgaris) is attacked by several pathogens such as the biotrophic gamma-proteobacterium Pseudomonas syringae pv. phaseolicola. To study the P. syringae pv. phaseolicola–bean interaction during the first stages of infection, leaf discs of a susceptible bean cultivar Riñón were infected with pathogenic P. syringae pv. phaseolicola. Using this experimental system, we tested six new putative wall-associated kinase (WAK) receptors, previously identified in silico. These six P. vulgaris WAKs (PvWAKs) showed high protein sequence homology to the well-described Arabidopsis thaliana WAK1 (AtWAK1) receptor and, by phylogenetic analysis, clustered together with AtWAKs. The expression of PvWAK1 increased at very early stages after the P. syringae pv. phaseolicola infection. Time course experiments were performed to evaluate the accumulation of apoplastic H₂O₂, Ca²⁺ influx, total H₂O₂, antioxidant enzymatic activities, lipid peroxidation, and the concentrations of abscisic acid and salicylic acid (SA), as well as the expression of six defense-related genes: MEKK-1, MAPKK, WRKY33, RIN4, PR1, and NPR1. The results showed that overexpression of PR1 occurred 2 h after P. syringae pv. phaseolicola infection without a concomitant increase in SA levels. Although apoplastic H₂O₂ increased after infection, the oxidative burst was neither intense nor rapid, and an efficient antioxidant response did not occur, suggesting that the observed cellular damage was caused by the initial increase in total H₂O₂ early after infection. In conclusion, Riñón can perceive the presence of P. syringae pv. phaseolicola, but this recognition results in only a modest and slow activation of host defenses, leading to high susceptibility to P. syringae pv. phaseolicola.

Halo blight disease of beans (Phaseolus vulgaris L.), caused by the bacterium Pseudomonas syringae pv. phaseolicola (Pph), is responsible for severe losses in crop production worldwide. As the current agronomic techniques used are not effective, it is necessary to search for new ones which may prevent disease in common bean. In this study, we challenged four plant-based preparations (PBPs), with no other agronomic uses, as they come from industrial waste (grapevine pomace (R_G) and hop residue (R_H)) or wild plants (Urtica dioica (U) and Equisetum sp. (E)), to be used as immune defense elicitors against Pph in common bean. After studying their inhibitory effect against Pph growth by bioassays, the two most effective PBPs (R_G and U) were applied in common bean plants. By measuring the total H₂O₂, lipid peroxidation, and antioxidant enzymatic activities, as well as the expression of six defense-related genes—PR1, WRKY33, MAPKK, RIN4, and PAL1—, it was observed that U-PBP application involved a signaling redox process and the overexpression of all genes, mostly PR1. First infection trials in vitro suggested that the application of U-PBP involved protection against Pph. The elicitation of bean defense with U-PBP involved a decrease in some yield parameters, but without affecting the final production. All these findings suggest a future use of U-PBP to diminish halo blight disease.

La provincia de León supone el 44,32% del total del área cultivada de esta leguminosa en España y el 49,12% de la producción nacional, lo que ha llevado a la creación del sello Indicación Geográfica Protegida (IGP) Alubia de La Bañeza-León, que agrupa a 4 variedades (Canela, Plancheta, Pinta y Riñón), de las cuales, la variedad Riñón ha sido el sujeto de estudio de esta tesis. Sin embargo, dicha producción se ve perjudicada por una enfermedad conocida como enfermedad de la grasa (o simplemente “la grasa”), producida por la bacteria Pseudomonas syringae pv. phaseolicola (Pph). Frente a esta patología de la alubia, cuyo agente causal describió Burkholder hace 100 años, seguimos sin contar con una solución eficaz, posiblemente por el hecho de que esta bacteria patógena sobreviva en la semilla, de manera que en la siguiente cosecha podrá volver a desencadenarse la enfermedad, aunque la proporción de semillas contaminadas sea muy baja.