Phosphorus (P) deficiency and soil-borne fungal diseases are major constraints to peanut (Arachis hypogaea L.) production. Phosphate-solubilizing bacteria (PSB) can improve P availability in the soil, thereby promoting plant growth. However, their potential to improve plant resistance against pathogens under P-limited conditions remains poorly understood. In this study, we first evaluated the ability of two PSB strains, Enterobacter sp. J49 and Serratia sp. S119, to induce systemic resistance (ISR) in peanut plants against the fungal pathogen Sclerotium rolfsii. Results showed that strain S119 reduced disease severity by 40%, whereas strain J49 reduced both incidence (30%) and severity (40%). The protective effect produced by strain J49 was mediated by ISR, as evidenced by the early increase in phenolic compounds accumulation (48 h) and total peroxidase activity (72 h) in inoculated plants. Under P-deficient conditions, the J49 strain was also able to protect peanut plants against S. rolfsii, as demonstrated by a significant reduction in disease severity (55%). These findings highlight the potential of multifunctional bacterium Enterobacter sp. J49 to enhance sustainable peanut production by simultaneously improving P acquisition and strengthening plant defense mechanisms.

In legumes, a LysM-RLK perception of rhizobial lipo-chitooligosaccharides (LCOs) known as Nod factors (NFs), triggers a signaling pathway related to the onset of symbiosis development. On the other hand, activation of LysM-RLKs upon recognition of chitin-derived short-chitooligosaccharides initiates defense responses. In this work, we identified the members of the LysM-RLK family in cultivated (Arachis hypogaea L.) and wild (A. duranensis and A. ipaensis) peanut genomes, and reconstructed the evolutionary history of the family. Phylogenetic analyses allowed the building of a framework to reinterpret the functional data reported on peanut LysM-RLKs. In addition, the potential involvement of two identified proteins in NF perception and immunity was assessed by gene expression analyses. Results indicated that peanut LysM-RLK is a highly diverse family. Digital expression analyses indicated that some A. hypogaea LysM-RLK receptors were upregulated during the early and late stages of symbiosis. In addition, expression profiles of selected LysM-RLKs proteins suggest participation in the receptor network mediating NF and/or chitosan perception. The analyses of LysM-RLK in the non-model legume peanut can contribute to gaining insight into the molecular basis of legume–microbe interactions and to the understanding of the evolutionary history of this gene family within the Fabaceae.