Alderkamp, M. | bioRxiv Science

bioRxiv2025

A lettuce receptor-like kinase recognizes the highly conserved heptapeptide motif within microbial NEP1-like proteins

Plants rely on cell surface immune receptors to detect microbial patterns and initiate effective defense responses. Although the Asteraceae family is one of the largest and economically important plant groups, little information is available about its pattern-triggered immunity signaling. Cultivated lettuce (Lactuca sativa L.) recognizes a 24-amino acid peptide (nlp24) from necrosis- and ethylene-inducing peptide 1-like proteins (NLPs) found in bacteria, fungi, and oomycetes. Here, we perform an extensive characterization of nlp24-induced immune responses in lettuce and identify the LETTUCE nlp24 RECEPTOR (LNR) as the leucine-rich repeat receptor-like kinase mediating its recognition. Remarkably, nlp24 recognition in lettuce and subsequent activation of defenses strongly depend on the conserved heptapeptide motif (GHRHDWE). Structural modeling-guided mutagenesis experiments suggest that residues in the nlp24 heptapeptide interact with a hydrophobic pocket in the LNR solenoid structure. Divergent ligand specificities and the absence of sequence homology between LNR and Arabidopsis nlp24-recognizing receptor indicate that the NLP recognition in lettuce and Arabidopsis emerged independently, through convergent evolution. Our phylogenetic analysis shows that LNR is closely related to Arabidopsis MIK2 (MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2), but belongs to a distinct, Asteraceae-specific monophyletic subgroup that has undergone a significant expansion in Lactuca. Our findings provide insights into the mechanisms of pattern-triggered immunity in lettuce and the fast evolution of its immune receptor repertoire. On the translational side, our findings open opportunities for the crop defense improvement via interfamily transfer. Significance statementUnderstanding pathogen recognition in crops is key to improving disease resistance. Our study identified the cell surface immune receptor in cultivated lettuce that senses the nlp24 pattern derived from secreted proteins (NLPs) of prokaryotic and eukaryotic microbial pathogens. Unlike the previously characterized receptor from Arabidopsis (RLP23), the lettuce nlp24 receptor (LNR) detects the deeply conserved heptapeptide motif of NLP proteins that is required for host cell lysis. Transfer of the LNR receptor to a Solanaceous species conferred quantitative resistance to the oomycete pathogen Phytophthora capsici. Our findings advance the understanding of pattern-triggered immunity in a major leafy crop and highlight LNR as a promising receptor for broad-spectrum plant resistance engineering.

plant biology↗

bioRxiv2024

Selective enrichment of specific bacterial taxa in downy mildew-affected spinach: Comparative analysis in laboratory and field conditions

Plants host diverse microbial communities that can be influenced by their hosts to mitigate biotic stress. Previous research demonstrated that distinct laboratory cultures of Hyaloperonospora arabidopsidis (Hpa) on Arabidopsis thaliana, consistently harbor nearly identical bacteria. In this study, we analyzed the bacterial phyllosphere communities of laboratory-grown spinach plants infected by the downy mildew pathogen Peronospora effusa (Pe). Using 16S amplicon sequencing, we identified 14 Amplicon Sequence Variants (ASVs), with diverse taxonomies, that were enriched in at least 3 out of 5 investigated Pe cultures. This small set of 14 ASVs occupied on average 6.9% of the total bacterial communities in healthy spinach plants, and 43.1% in Pe-inoculated plants. A specific Rhodococcus and a Paenarthrobacter ASV were particularly prevalent and abundant. To validate these findings outside of the laboratory, we planted a susceptible variety of spinach in 4 agricultural fields and sampled leaves from Pe-infected plants in 2 fields where this pathogen naturally occurred. Comparative microbiome analysis of diseased and healthy plants revealed significant enrichment of 16 and 31 ASVs in these 2 fields, respectively. Among these, the Paenarthrobacter ASV was enriched in one field and the Rhodococcus ASV in the other field, suggesting that disease-associated microbiota that are abundantly detected in Pe laboratory cultures are also associated with Pe-infected field plants. Additionally, we observed an overlap of ASVs that were associated with both Pe and Hpa, indicating that similar bacteria are linked to downy mildew disease across different hosts.

microbiology↗